"size" function nodes down from 454 to 321

Update README to reflect completion of experiment
Clean up and list SKI conversion fix
2025-08-07 20:08:59 -05:00 · 2025-05-29 13:39:44 -05:00 · 2025-04-24 12:14:38 -05:00 · 2025-04-16 14:23:53 -05:00 · 2025-04-15 10:52:53 -05:00 · 2025-04-15 10:34:38 -05:00
26 changed files with 1106 additions and 429 deletions
--- a/.gitignore
+++ b/.gitignore
@ -9,3 +9,4 @@
 WD
 bin/
 dist*
+.tricu_history
--- a/README.md
+++ b/README.md
@ -2,37 +2,31 @@

 ## Introduction

-tricu (pronounced "tree-shoe") is a purely functional interpreted language implemented in Haskell. It is fundamentally based on the application of [Tree Calculus](https://github.com/barry-jay-personal/typed_tree_calculus/blob/main/typed_program_analysis.pdf) terms, but minimal syntax sugar is included to provide a useful programming tool. 
+tricu (pronounced "tree-shoe") is a purely functional interpreted language implemented in Haskell. It is fundamentally based on the application of [Tree Calculus](https://github.com/barry-jay-personal/typed_tree_calculus/blob/main/typed_program_analysis.pdf) terms, but minimal syntax sugar is included.

-*tricu is under active development and you should expect breaking changes with every commit.*
+*This experiment has concluded. tricu will see no further development or bugfixes.*

 tricu is the word for "tree" in Lojban: `(x1) is a tree of species/cultivar (x2)`.

-## Features
+## Acknowledgements 

- Tree Calculus operator: `t`
- Assignments: `x = t t`
- Immutable definitions
- Lambda abstraction syntax: `id = (\a : a)`
- List, Number, and String literals: `[(2) ("Hello")]` 
- Function application: `not (not false)`
- Higher order/first-class functions: `map (\a : append a "!") [("Hello")]`
- Intensionality blurs the distinction between functions and data (see REPL examples)
- Simple module system for code organization
+Tree Calculus was discovered by [Barry Jay](https://github.com/barry-jay-personal/blog). 
+
+[treecalcul.us](https://treecalcul.us) is an excellent website with an intuitive Tree Calculus code playground created by [Johannes Bader](https://johannes-bader.com/) that introduced me to Tree Calculus.

 ## REPL examples

 ```
 tricu < -- Anything after `--` on a single line is a comment
-tricu < id = (\a : a) -- Lambda abstraction is eliminated to tree calculus terms
-tricu < head (map (\i : append i " world!") [("Hello, ")])
+tricu < id = (a : a) -- Lambda abstraction is eliminated to tree calculus terms
+tricu < head (map (i : append i " world!") [("Hello, ")])
 tricu > "Hello,  world!"
-tricu < id (head (map (\i : append i " world!") [("Hello, ")]))
+tricu < id (head (map (i : append i " world!") [("Hello, ")]))
 tricu > "Hello,  world!"

 tricu < -- Intensionality! We can inspect the structure of a function or data.
-tricu < triage = (\a b c : t (t a b) c)
-tricu < test = triage "Leaf" (\z : "Stem") (\a b : "Fork")
+tricu < triage = (a b c : t (t a b) c)
+tricu < test = triage "Leaf" (z : "Stem") (a b : "Fork")
 tricu < test (t t)
 tricu > "Stem"
 tricu < -- We can even convert a term back to source code (/demos/toSource.tri)
@ -41,13 +35,21 @@ tricu > "(t (t (t t) (t t t)) (t t (t t t)))"
 tricu < -- or calculate its size (/demos/size.tri)
 tricu < size not?
 tricu > 12
+
+tricu < -- REPL Commands:
+tricu < !definitions  -- Lists all available definitions
+tricu < !output       -- Change output format (Tree, FSL, AST, etc.)
+tricu < !import       -- Import definitions from a file
+tricu < !exit         -- Exit the REPL
+tricu < !clear        -- ANSI screen clear
+tricu < !save         -- Save all REPL definitions to a file that you can !import
+tricu < !reset        -- Clear all REPL definitions
+tricu < !version      -- Print tricu version
 ```

 ## Installation and Use

-[Releases are available for Linux.](https://git.eversole.co/James/tricu/releases)
-
-Or you can easily build and run this project using [Nix](https://nixos.org/download/).
+You can easily build and run this project using [Nix](https://nixos.org/download/).

 - Quick Start (REPL): 
  - `nix run git+https://git.eversole.co/James/tricu`
@ -83,9 +85,3 @@ tricu decode [OPTIONS]
  -f --file=FILE  Optional input file path to attempt decoding.
                    Defaults to stdin.
 ```
-
-## Acknowledgements 
-
-Tree Calculus was discovered by [Barry Jay](https://github.com/barry-jay-personal/blog). 
-
-[treecalcul.us](https://treecalcul.us) is an excellent website with an intuitive Tree Calculus code playground created by [Johannes Bader](https://johannes-bader.com/) that introduced me to Tree Calculus.
--- a/demos/equality.tri
+++ b/demos/equality.tri
@ -11,20 +11,17 @@ demo_true  = t t
 not_TC?     = t (t (t t) (t t t)) (t t (t t t))

 -- /demos/toSource.tri contains an explanation of `triage`
-demo_triage = \a b c : t (t a b) c
-demo_matchBool = (\ot of : demo_triage
-  of
-  (\_ : ot)
-  (\_ _ : ot)
-)
+demo_triage = a b c : t (t a b) c
+demo_matchBool = a b : demo_triage b (_ : a) (_ _ : a)
+
 -- Lambda representation of the Boolean `not` function
 not_Lambda? = demo_matchBool demo_false demo_true

-- Since tricu eliminates Lambda terms to SKI combinators, the tree form of many
+-- As tricu eliminates Lambda terms to SKI combinators, the tree form of many
 -- functions defined via Lambda terms are larger than the most efficient TC
-- representation. Between different languages that evaluate to tree calculus 
-- terms, the exact implementation of Lambda elimination may differ and lead 
-- to different tree representations even if they share extensional behavior.
+-- representation possible. Between different languages that evaluate to tree
+-- calculus terms, the exact implementation of Lambda elimination may differ
+-- and lead to different trees even if they share extensional behavior.

 -- Let's see if these are the same:
 lambdaEqualsTC = equal? not_TC? not_Lambda?
--- a/demos/levelOrderTraversal.tri
+++ b/demos/levelOrderTraversal.tri
@ -18,15 +18,15 @@ main = exampleTwo
 --    /   /  \
 --   4   5    6

-label = \node : head node
+label = node : head node

-left = (\node : if (emptyList? node)
+left = node : (if (emptyList? node)
  []
  (if (emptyList? (tail node))
    []
    (head (tail node))))

-right = (\node : if (emptyList? node) 
+right = node : (if (emptyList? node)
  []
  (if (emptyList? (tail node))
    []
@ -34,25 +34,25 @@ right = (\node : if (emptyList? node)
      []
      (head (tail (tail node))))))

-processLevel = y (\self queue : if (emptyList? queue) 
+processLevel = y (self queue : if (emptyList? queue)
  []
  (pair (map label queue) (self (filter
-    (\node : not? (emptyList? node)) 
+    (node : not? (emptyList? node))
      (append (map left queue) (map right queue))))))

-levelOrderTraversal_ = \a : processLevel (t a t)
+levelOrderTraversal_ = a : processLevel (t a t)

-toLineString = y (\self levels : if (emptyList? levels) 
+toLineString = y (self levels : if (emptyList? levels)
  ""
  (append
-    (append (map (\x : append x " ") (head levels)) "") 
+    (append (map (x : append x " ") (head levels)) "")
    (if (emptyList? (tail levels)) "" (append (t (t 10 t) t) (self (tail levels))))))

-levelOrderToString = \s : toLineString (levelOrderTraversal_ s)
+levelOrderToString = s : toLineString (levelOrderTraversal_ s)

-flatten = foldl (\acc x : append acc x) ""
+flatten = foldl (acc x : append acc x) ""

-levelOrderTraversal = \s : append (t 10 t) (flatten (levelOrderToString s))
+levelOrderTraversal = s : append (t 10 t) (flatten (levelOrderToString s))

 exampleOne = levelOrderTraversal [("1")
                                 [("2") [("4") t t] t]
--- a/demos/patternMatching.tri
+++ b/demos/patternMatching.tri
@ -0,0 +1,37 @@
+!import "../lib/patterns.tri" !Local
+
+-- We can do conditional pattern matching by providing a list of lists, where
+-- each sublist contains a boolean expression and a function to return if said
+-- boolean expression evaluates to true.
+
+value = 42
+main  = match value [[(equal? "Hello") (_ : ", world!")] [(equal? 42) (_ : "The answer.")]]
+
+-- < main
+-- > "The answer."
+
+matchExample = (x : match x
+  [[(equal? 1)  (_ : "one")]
+   [(equal? 2)  (_ : "two")]
+   [(equal? 3)  (_ : "three")]
+   [(equal? 4)  (_ : "four")]
+   [(equal? 5)  (_ : "five")]
+   [(equal? 6)  (_ : "six")]
+   [(equal? 7)  (_ : "seven")]
+   [(equal? 8)  (_ : "eight")]
+   [(equal? 9)  (_ : "nine")]
+   [(equal? 10) (_ : "ten")]
+   [ otherwise  (_ : "I ran out of fingers!")]])
+
+-- < matchExample 3
+-- > "three"
+-- < matchExample 5
+-- > "five"
+-- < matchExample 9
+-- > "nine"
+-- < matchExample 11
+-- > "I ran out of fingers!"
+-- < matchExample "three"
+-- > "I ran out of fingers!"
+-- < matchExample [("hello") ("world")]
+-- > "I ran out of fingers!"
--- a/demos/size.tri
+++ b/demos/size.tri
@ -3,11 +3,9 @@

 main = size size

-size = (\x :
-  (y (\self x :
-    compose succ
-      (triage
-        (\x : x)
+size = x : y (self x : compose succ (triage
+  id
  self
-        (\x y : compose (self x) (self y))
-        x)) x 0))
+  (x y : compose (self x) (self y))
+  x)
+) x 0
--- a/demos/toSource.tri
+++ b/demos/toSource.tri
@ -18,25 +18,25 @@ main = toSource not?
 sourceLeaf = t (head "t")

 -- Stem case
-sourceStem = (\convert : (\a rest :
+sourceStem = convert : (a rest :
  t (head "(")                       -- Start with a left parenthesis "(".
    (t (head "t")                    -- Add a "t"
      (t (head " ")                  -- Add a space.
        (convert a                   -- Recursively convert the argument.
-          (t (head ")") rest))))))   -- Close with ")" and append the rest.
+          (t (head ")") rest)))))   -- Close with ")" and append the rest.

 -- Fork case
-sourceFork = (\convert : (\a b rest :
+sourceFork = convert : (a b rest :
  t (head "(")                           -- Start with a left parenthesis "(".
    (t (head "t")                        -- Add a "t"
      (t (head " ")                      -- Add a space.
        (convert a                       -- Recursively convert the first arg.
          (t (head " ")                  -- Add another space.
            (convert b                   -- Recursively convert the second arg.
-              (t (head ")") rest)))))))) -- Close with ")" and append the rest.
+              (t (head ")") rest))))))) -- Close with ")" and append the rest.

 -- Wrapper around triage 
-toSource_ = y (\self arg :
+toSource_ = y (self arg :
  triage
    sourceLeaf        -- `triage` "a" case, Leaf
    (sourceStem self) -- `triage` "b" case, Stem
@ -44,7 +44,7 @@ toSource_ = y (\self arg :
    arg)              -- The term to be inspected

 -- toSource takes a single TC term and returns a String
-toSource = \v : toSource_ v ""
+toSource = v : toSource_ v ""

 exampleOne = toSource true -- OUT: "(t t)"
 exampleTwo = toSource not? -- OUT: "(t (t (t t) (t t t)) (t t (t t t)))"
--- a/flake.nix
+++ b/flake.nix
@ -34,6 +34,7 @@
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [
            haskellPackages.cabal-install
+            haskellPackages.ghc-events
            haskellPackages.ghcid
            customGHC
            upx
--- a/lib/base.tri
+++ b/lib/base.tri
@ -1,74 +1,74 @@
 false = t
 _     = t
 true  = t t
-id    = \a : a
-const = \a b : a
+id    = a : a
+const = a b : a
 pair  = t
-if    = \cond then else : t (t else (t t then)) t cond
+if    = cond then else : t (t else (t t then)) t cond

-y = ((\mut wait fun : wait mut (\x : fun (wait mut x)))
-     (\x : x x)
-     (\a0 a1 a2 : t (t a0) (t t a2) a1))
+y = ((mut wait fun : wait mut (x : fun (wait mut x)))
+     (x : x x)
+     (a0 a1 a2 : t (t a0) (t t a2) a1))

-compose = \f g x : f (g x)
+compose = f g x : f (g x)

-triage = \leaf stem fork : t (t leaf stem) fork
-test   = triage "Leaf" (\_ : "Stem") (\_ _ : "Fork")
+triage = leaf stem fork : t (t leaf stem) fork
+test   = triage "Leaf" (_ : "Stem") (_ _ : "Fork")

-matchBool = (\ot of : triage
+matchBool = (ot of : triage
  of
-  (\_ : ot)
-  (\_ _ : ot)
+  (_ : ot)
+  (_ _ : ot)
 )

 lAnd = (triage
-  (\_     : false)
-  (\_ x   : x)
-  (\_ _ x : x))
+  (_     : false)
+  (_ x   : x)
+  (_ _ x : x))

 lOr = (triage
-  (\x     : x)
-  (\_ _   : true)
-  (\_ _ _ : true))
+  (x     : x)
+  (_ _   : true)
+  (_ _ _ : true))

-matchPair = \a   : triage _ _ a
+matchPair = a : triage _ _ a

 not? = matchBool false true
-and? = matchBool id (\_ : false)
+and? = matchBool id (_ : false)

-or? = (\x z : 
+or? = (x z : 
  matchBool 
    (matchBool true true z)
    (matchBool true false z)
    x)

-xor? = (\x z : 
+xor? = (x z : 
  matchBool 
    (matchBool false true z)
    (matchBool true false z)
    x)

-equal? = y (\self : triage
+equal? = y (self : triage
  (triage
    true
-    (\_   : false)
-    (\_ _ : false))
-  (\ax :
+    (_   : false)
+    (_ _ : false))
+  (ax :
    triage
      false
      (self ax)
-      (\_ _ : false))
-  (\ax ay :
+      (_ _ : false))
+  (ax ay :
    triage
      false
-      (\_ : false)
-      (\bx by : lAnd (self ax bx) (self ay by))))
+      (_ : false)
+      (bx by : lAnd (self ax bx) (self ay by))))

-succ = y (\self :
+succ = y (self :
  triage
    1
    t
    (triage
      (t (t t))
-      (\_ tail : t t (self tail))
+      (_ tail : t t (self tail))
      t))
--- a/lib/list.tri
+++ b/lib/list.tri
@ -1,77 +1,70 @@
 !import "base.tri" !Local

-matchList = \a b : triage a _ b
+_ = t

-emptyList? = matchList true (\_ _ : false)
-head = matchList t (\head _ : head)
-tail = matchList t (\_ tail : tail)
+matchList = a b : triage a _ b

-append = y (\self : matchList
-  (\k : k)
-  (\h r k : pair h (self r k)))
+emptyList? = matchList true (_ _ : false)
+head = matchList t (head _ : head)
+tail = matchList t (_ tail : tail)

-lExist? = y (\self x : matchList
+append = y (self : matchList
+  (k : k)
+  (h r k : pair h (self r k)))
+
+lExist? = y (self x : matchList
  false
-  (\h z : or? (equal? x h) (self x z)))
+  (h z : or? (equal? x h) (self x z)))

-map_ = y (\self :
+map_ = y (self :
  matchList
-    (\_ : t)
-    (\head tail f : pair (f head) (self tail f)))
-map = \f l : map_ l f
+    (_ : t)
+    (head tail f : pair (f head) (self tail f)))
+map = f l : map_ l f

-filter_ = y (\self : matchList
-  (\_ : t)
-  (\head tail f : matchBool (t head) id (f head) (self tail f)))
-filter  = \f l : filter_ l f
+filter_ = y (self : matchList
+  (_ : t)
+  (head tail f : matchBool (t head) id (f head) (self tail f)))
+filter  = f l : filter_ l f

-foldl_ = y (\self f l x : matchList (\acc : acc) (\head tail acc : self f tail (f acc head)) l x)
-foldl  = \f x l : foldl_ f l x
+foldl_ = y (self f l x : matchList (acc : acc) (head tail acc : self f tail (f acc head)) l x)
+foldl  = f x l : foldl_ f l x

-foldr_ = y (\self x f l : matchList x (\head tail : f (self x f tail) head) l)
-foldr  = \f x l : foldr_ x f l
+foldr_ = y (self x f l : matchList x (head tail : f (self x f tail) head) l)
+foldr  = f x l : foldr_ x f l

-length = y (\self : matchList
+length = y (self : matchList
  0
-  (\_ tail : succ (self tail)))
+  (_ tail : succ (self tail)))

-reverse = y (\self : matchList
+reverse = y (self : matchList
  t
-  (\head tail : append (self tail) (pair head t)))
+  (head tail : append (self tail) (pair head t)))

-snoc = y (\self x : matchList
+snoc = y (self x : matchList
  (pair x t)
-  (\h z : pair h (self x z)))
+  (h z : pair h (self x z)))

-count = y (\self x : matchList
+count = y (self x : matchList
  0
-  (\h z : matchBool
+  (h z : matchBool
    (succ (self x z))
    (self x z)
    (equal? x h)))

-last = y (\self : matchList
+last = y (self : matchList
  t
-  (\hd tl : matchBool
+  (hd tl : matchBool
    hd
    (self tl)
    (emptyList? tl)))

-all? = y (\self pred : matchList
+all? = y (self pred : matchList
  true
-  (\h z : and? (pred h) (self pred z)))
+  (h z : and? (pred h) (self pred z)))

-any? = y (\self pred : matchList
+any? = y (self pred : matchList
  false
-  (\h z : or? (pred h) (self pred z)))
+  (h z : or? (pred h) (self pred z)))

-unique_ = y (\self seen : matchList
-  t
-  (\head rest : matchBool
-    (self seen rest)
-    (pair head (self (pair head seen) rest))
-    (lExist? head seen)))
-unique = \xs : unique_ t xs
-
-intersect = \xs ys : filter (\x : lExist? x ys) xs
-union     = \xs ys : unique (append xs ys)
+intersect = xs ys : filter (x : lExist? x ys) xs
--- a/lib/patterns.tri
+++ b/lib/patterns.tri
@ -0,0 +1,24 @@
+!import "base.tri" !Local
+!import "list.tri" List
+
+match_ = y (self value patterns :
+  triage
+    t
+    (_ : t)
+    (pattern rest :
+      triage
+        t
+        (_ : t)
+        (test result :
+          if (test value)
+             (result value)
+             (self value rest))
+        pattern)
+    patterns)
+
+match = (value patterns :
+  match_ value (List.map (sublist :
+    pair (List.head sublist) (List.head (List.tail sublist)))
+    patterns))
+
+otherwise = const (t t)
--- a/src/Eval.hs
+++ b/src/Eval.hs
@ -3,11 +3,30 @@ module Eval where
 import Parser
 import Research

-import Data.List (partition, (\\))
+import           Data.List   (partition, (\\), elemIndex)
 import           Data.Map    (Map)
+import           Data.Set    (Set)
+
+import qualified Data.Foldable as F
 import qualified Data.Map as Map
 import qualified Data.Set as Set

+data DB
+  = BVar Int          -- bound (0 = nearest binder)
+  | BFree String      -- free/global
+  | BLam DB
+  | BApp DB DB
+  | BLeaf
+  | BStem DB
+  | BFork DB DB
+  | BStr String
+  | BInt Integer
+  | BList [DB]
+  | BEmpty
+  deriving (Eq, Show)
+
+type Uses = [Bool]
+
 evalSingle :: Env -> TricuAST -> Env
 evalSingle env term
  | SDef name [] body <- term
@ -62,56 +81,75 @@ evalAST env term
 elimLambda :: TricuAST -> TricuAST
 elimLambda = go
  where
-    -- η-reduction
-    go (SLambda [v] (SApp f (SVar x)))
-      | v == x && not (isFree v f) = elimLambda f
-    -- Triage optimization
-    go (SLambda [a] (SLambda [b] (SLambda [c] body)))
-      | body == triageBody         = _TRIAGE
+    go term
+      | etaReduction term   = go (etaReduceResult term)
+      | triagePattern term  = _TRI
+      | composePattern term = _B
+      | lambdaList term     = go (lambdaListResult term)
+      | nestedLambda term   = nestedLambdaResult term
+      | application term    = applicationResult term
+      | otherwise           = term
+
+    -- patterns (now DB-indexed where it matters)
+    etaReduction (SLambda [v] (SApp f (SVar x))) = v == x && not (usesBinder v f)
+    etaReduction _ = False
+
+    -- triage: \a b c -> TLeaf (TLeaf a b) c  (checked in DB with a↦2, b↦1, c↦0)
+    triagePattern (SLambda [a] (SLambda [b] (SLambda [c] body))) =
+      toDB [c,b,a] body == triageBodyDB
+    triagePattern _ = False
+
+    -- compose: \f g x -> f (g x)  (checked in DB with f↦2, g↦1, x↦0)
+    composePattern (SLambda [f] (SLambda [g] (SLambda [x] body))) =
+      toDB [x,g,f] body == composeBodyDB
+    composePattern _ = False
+
+    lambdaList (SLambda [_] (SList _)) = True
+    lambdaList _ = False
+
+    nestedLambda (SLambda (_:_) _) = True
+    nestedLambda _ = False
+
+    application (SApp _ _) = True
+    application _ = False
+
+    -- rewrites
+    etaReduceResult (SLambda [_] (SApp f _)) = f
+
+    lambdaListResult (SLambda [v] (SList xs)) =
+      SLambda [v] (foldr wrapTLeaf TLeaf xs)
      where
-        triageBody =
-          SApp (SApp TLeaf (SApp (SApp TLeaf (SVar a)) (SVar b))) (SVar c)
-    -- Composition optimization
-    go (SLambda [f] (SLambda [g] (SLambda [x] body)))
-      | body == SApp (SVar f) (SApp (SVar g) (SVar x)) = _B
-    -- General elimination
-    go (SLambda (v:vs) body)
-      | null vs                    = toSKI v (elimLambda body)
-      | otherwise                  = elimLambda (SLambda [v] (SLambda vs body))
-    go (SApp f g)                  = SApp (elimLambda f) (elimLambda g)
-    go x                           = x
+        wrapTLeaf m r = SApp (SApp TLeaf m) r

-    toSKI x (SVar y)
-      | x == y           = _I
-      | otherwise        = SApp _K (SVar y)
-    toSKI x t@(SApp n u)
-      | not (isFree x t) = SApp _K t
-      | otherwise        = SApp (SApp _S (toSKI x n)) (toSKI x u)
-    toSKI x t
-      | not (isFree x t) = SApp _K t
-      | otherwise        = errorWithoutStackTrace "Unhandled toSKI conversion"
+    -- The key change: use DB bracket abstraction for the final parameter.
+    nestedLambdaResult (SLambda (v:vs) body)
+      | null vs   =
+          let body' = go body
+              db    = toDB [v] body'
+          in toSKIKiselyov db 
+      | otherwise = go (SLambda [v] (SLambda vs body))

-    _S       = parseSingle "t (t (t t t)) t"
-    _K       = parseSingle "t t"
-    _I       = parseSingle "t (t (t t)) t"
-    _B       = parseSingle "t (t (t t (t (t (t t t)) t))) (t t)"
-    _TRIAGE  = parseSingle "t (t (t t (t (t (t t t))))) t"
+    applicationResult (SApp f g) = SApp (go f) (go g)
+
+-- combinators and special forms (unchanged)
+_S   = parseSingle "t (t (t t t)) t"
+_K   = parseSingle "t t"
+_I   = parseSingle "t (t (t t)) t"
+_R   = parseSingle "(t (t (t t (t (t (t (t (t (t (t t (t (t (t t t)) t))) (t (t (t t (t t))) (t (t (t t t)) t)))) (t t (t t))))))) (t t))"
+_C   = parseSingle "(t (t (t (t (t t (t (t (t t t)) t))) (t (t (t t (t t))) (t (t (t t t)) t)))) (t t (t t)))"
+_B   = parseSingle "t (t (t t (t (t (t t t)) t))) (t t)"
+_T   = SApp _C _I
+_TRI = parseSingle "t (t (t t (t (t (t t t))))) t"
+
+-- pattern bodies (kept for reference; checks are now DB-based)
+triageBody a b c   = SApp (SApp TLeaf (SApp (SApp TLeaf (SVar a)) (SVar b))) (SVar c)
+composeBody f g x  = SApp (SVar f) (SApp (SVar g) (SVar x))

 isFree :: String -> TricuAST -> Bool
-isFree x = Set.member x . freeVars
+isFree x t = Set.member x (freeVars t)

-freeVars :: TricuAST -> Set.Set String
-freeVars (SVar    v    ) = Set.singleton v
-freeVars (SInt    _    ) = Set.empty
-freeVars (SStr    _    ) = Set.empty
-freeVars (SList   s    ) = foldMap freeVars s
-freeVars (SApp    f a  ) = freeVars f <> freeVars a
-freeVars  TLeaf          = Set.empty
-freeVars (SDef   _ _ b)  = freeVars b
-freeVars (TStem   t    ) = freeVars t
-freeVars (TFork   l r  ) = freeVars l <> freeVars r
-freeVars (SLambda v b  ) = foldr Set.delete (freeVars b) v
-freeVars  _              = Set.empty
+freeVars :: TricuAST -> Set String
+freeVars = freeDBNames . toDB []

 reorderDefs :: Env -> [TricuAST] -> [TricuAST]
 reorderDefs env defs
@ -128,7 +166,7 @@ reorderDefs env defs
    graph = buildDepGraph defsOnly
    sortedDefs = sortDeps graph
    defMap = Map.fromList [(name, def) | def@(SDef name _ _) <- defsOnly]
-    orderedDefs = map (\name -> defMap Map.! name) sortedDefs
+    orderedDefs = map (defMap Map.!) sortedDefs

    freeVarsDefs = foldMap snd defsWithFreeVars
    freeVarsOthers = foldMap freeVars others
@ -136,7 +174,7 @@ reorderDefs env defs
    validNames = Set.fromList defNames `Set.union` Set.fromList (Map.keys env)
    missingDeps = Set.toList (allFreeVars `Set.difference` validNames)

-    isDef (SDef _ _ _) = True
+    isDef SDef {} = True
    isDef _       = False

 buildDepGraph :: [TricuAST] -> Map.Map String (Set.Set String)
@ -192,3 +230,284 @@ mainResult :: Env -> T
 mainResult r = case Map.lookup "main" r of
  Just  a -> a
  Nothing -> errorWithoutStackTrace "No valid definition for `main` found."
+
+-- Convert named TricuAST to De Bruijn form
+toDB :: [String] -> TricuAST -> DB
+toDB env = \case
+  SVar v       -> maybe (BFree v) BVar (elemIndex v env)
+  SLambda vs b ->
+    let env' = reverse vs ++ env
+        body = toDB env' b
+    in foldr (\_ acc -> BLam acc) body vs
+  SApp f a     -> BApp (toDB env f) (toDB env a)
+  TLeaf        -> BLeaf
+  TStem t      -> BStem (toDB env t)
+  TFork l r    -> BFork (toDB env l) (toDB env r)
+  SStr s       -> BStr s
+  SInt n       -> BInt n
+  SList xs     -> BList (map (toDB env) xs)
+  SEmpty       -> BEmpty
+  SDef{}       -> error "toDB: unexpected SDef at this stage"
+  SImport _ _  -> BEmpty
+
+-- Does a term depend on the current binder (level 0)?
+dependsOnLevel :: Int -> DB -> Bool
+dependsOnLevel lvl = \case
+  BVar k      -> k == lvl
+  BLam t      -> dependsOnLevel (lvl + 1) t
+  BApp f a    -> dependsOnLevel lvl f || dependsOnLevel lvl a
+  BStem t     -> dependsOnLevel lvl t
+  BFork l r   -> dependsOnLevel lvl l || dependsOnLevel lvl r
+  BList xs    -> any (dependsOnLevel lvl) xs
+  _           -> False
+
+-- Collect free *global* names (i.e., unbound)
+freeDBNames :: DB -> Set String
+freeDBNames = \case
+  BFree s   -> Set.singleton s
+  BVar _    -> mempty
+  BLam t    -> freeDBNames t
+  BApp f a  -> freeDBNames f <> freeDBNames a
+  BLeaf     -> mempty
+  BStem t   -> freeDBNames t
+  BFork l r -> freeDBNames l <> freeDBNames r
+  BStr _    -> mempty
+  BInt _    -> mempty
+  BList xs  -> foldMap freeDBNames xs
+  BEmpty    -> mempty
+
+-- Helper: “is the binder named v used in body?”
+usesBinder :: String -> TricuAST -> Bool
+usesBinder v body = dependsOnLevel 0 (toDB [v] body)
+
+-- Expected DB bodies for the named special patterns (under env [a,b,c] -> indices 2,1,0)
+triageBodyDB :: DB
+triageBodyDB =
+  BApp (BApp BLeaf (BApp (BApp BLeaf (BVar 2)) (BVar 1))) (BVar 0)
+
+composeBodyDB :: DB
+composeBodyDB =
+  BApp (BVar 2) (BApp (BVar 1) (BVar 0))
+
+-- Convert DB -> TricuAST for subterms that contain NO binders (no BLam, no BVar)
+fromDBClosed :: DB -> TricuAST
+fromDBClosed = \case
+  BFree s   -> SVar s
+  BApp f a  -> SApp (fromDBClosed f) (fromDBClosed a)
+  BLeaf     -> TLeaf
+  BStem t   -> TStem (fromDBClosed t)
+  BFork l r -> TFork (fromDBClosed l) (fromDBClosed r)
+  BStr s    -> SStr s
+  BInt n    -> SInt n
+  BList xs  -> SList (map fromDBClosed xs)
+  BEmpty    -> SEmpty
+  -- Anything bound would be a logic error if we call this correctly.
+  BLam _    -> error "fromDBClosed: unexpected BLam"
+  BVar _    -> error "fromDBClosed: unexpected bound variable"
+
+-- DB-native bracket abstraction over the innermost binder (level 0).
+-- This mirrors your old toSKI, but is purely index-driven.
+toSKIDB :: DB -> TricuAST
+toSKIDB t
+  | not (dependsOnLevel 0 t) = SApp _K (fromDBClosed t)
+toSKIDB (BVar 0)             = _I
+toSKIDB (BApp n u)           = SApp (SApp _S (toSKIDB n)) (toSKIDB u)
+toSKIDB (BList xs) =
+  let anyUses = any (dependsOnLevel 0) xs
+  in if not anyUses
+        then SApp _K (SList (map fromDBClosed xs))
+        else SList (map toSKIDB xs)
+toSKIDB other =
+  errorWithoutStackTrace $ "Unhandled toSKI(DB) conversion: " ++ show other
+
+app2 :: TricuAST -> TricuAST -> TricuAST
+app2 f x = SApp f x
+
+app3 :: TricuAST -> TricuAST -> TricuAST -> TricuAST
+app3 f x y = SApp (SApp f x) y
+
+-- Core converter that *does not* perform the λ-step; it just returns (Γ, d).
+-- Supported shapes: variables, applications, closed literals (Leaf/Int/Str/Empty),
+-- closed lists. For anything where the binder occurs under structural nodes
+-- (Stem/Fork/List-with-use), we deliberately bail so the caller can fall back.
+kisConv :: DB -> Either String (Uses, TricuAST)
+kisConv = \case
+  BVar 0     -> Right ([True], _I)
+  BVar n | n > 0 -> do
+    (g,d) <- kisConv (BVar (n - 1))
+    Right (False:g, d)
+  BApp e1 e2 -> do
+    (g1,d1) <- kisConv e1
+    (g2,d2) <- kisConv e2
+    let g = zipWithDefault False (||) g1 g2   -- <— propagate Γ outside (#)
+        d = kisHash (g1,d1) (g2,d2)           -- <— (#) yields only the term
+    Right (g, d)
+  -- Treat closed constants as free 'combinator leaves' (no binder use).
+  BLeaf      -> Right ([], TLeaf)
+  BStr s     -> Right ([], SStr s)
+  BInt n     -> Right ([], SInt n)
+  BEmpty     -> Right ([], SEmpty)
+  -- Closed list: allowed. If binder is used anywhere, we punt to fallback.
+  BList xs
+    | any (dependsOnLevel 0) xs -> Left "List with binder use: fallback"
+    | otherwise                 -> Right ([], SList (map fromDBClosed xs))
+  -- For structural nodes, only allow if *closed* wrt the binder.
+  BStem t
+    | dependsOnLevel 0 t -> Left "Stem with binder use: fallback"
+    | otherwise          -> Right ([], TStem (fromDBClosed t))
+  BFork l r
+    | dependsOnLevel 0 l || dependsOnLevel 0 r -> Left "Fork with binder use: fallback"
+    | otherwise                                -> Right ([], TFork (fromDBClosed l) (fromDBClosed r))
+  -- We shouldn’t see BLam under elim; treat as unsupported so we fallback.
+  BLam _      -> Left "Nested lambda under body: fallback"
+  BFree s     -> Right ([], SVar s)
+
+-- Application combiner with K-optimization (lazy weakening).
+-- Mirrors Lynn’s 'optK' rules: choose among S, B, C, R based on leading flags.
+-- η-aware (#) with K-optimization (adapted from TS kiselyov_eta)
+kisHash :: (Uses, TricuAST) -> (Uses, TricuAST) -> TricuAST
+kisHash (g1, d1) (g2, d2) =
+  case g1 of
+    [] -> case g2 of
+      []            -> SApp d1 d2
+      True:gs2      -> if isId2 (g2, d2)
+                         then d1
+                         else kisHash ([], SApp _B d1) (gs2, d2)
+      False:gs2     -> kisHash ([], d1) (gs2, d2)
+
+    True:gs1 -> case g2 of
+      []            -> if isId2 (g1, d1)
+                         then SApp _T d2
+                         else kisHash ([], SApp _R d2) (gs1, d1)
+      _ ->
+        if isId2 (g1, d1) && case g2 of { False:_ -> True; _ -> False }
+          then kisHash ([], _T) (tail g2, d2)
+        else
+          -- NEW: coalesce the longest run of identical head pairs and apply bulk op once
+          let ((h1, h2), count) = headPairRun g1 g2
+              g1' = drop count g1
+              g2' = drop count g2
+          in case (h1, h2) of
+               (False, False) ->
+                 kisHash (g1', d1) (g2', d2)
+               (False, True)  ->
+                 let d1' = kisHash ([], bulkB count) (g1', d1)
+                 in  kisHash (g1', d1') (g2', d2)
+               (True, False)  ->
+                 let d1' = kisHash ([], bulkC count) (g1', d1)
+                 in  kisHash (g1', d1') (g2', d2)
+               (True, True)   ->
+                 let d1' = kisHash ([], bulkS count) (g1', d1)
+                 in  kisHash (g1', d1') (g2', d2)
+
+    False:gs1 -> case g2 of
+      []            -> kisHash (gs1, d1) ([], d2)
+      _             ->
+        if isId2 (g1, d1) && case g2 of { False:_ -> True; _ -> False }
+          then kisHash ([], _T) (tail g2, d2)
+        else case g2 of
+          True:gs2   ->
+            let d1' = kisHash ([], _B) (gs1, d1)
+            in  kisHash (gs1, d1') (gs2, d2)
+          False:gs2  ->
+            kisHash (gs1, d1) (gs2, d2)
+  where
+    tail (_:xs) = xs
+    tail []     = []
+
+
+toSKIKiselyov :: DB -> TricuAST
+toSKIKiselyov body =
+  case kisConv body of
+    Right ([], d)          -> SApp _K d
+    Right (True:_ , d)     -> d
+    Right (False:g, d)     -> kisHash ([], _K) (g, d)  -- no snd
+    Left _                 -> starSKIBCOpEtaDB body   -- was: toSKIDB body
+
+zipWithDefault :: a -> (a -> a -> a) -> [a] -> [a] -> [a]
+zipWithDefault d f []     ys     = map (f d) ys
+zipWithDefault d f xs     []     = map (\x -> f x d) xs
+zipWithDefault d f (x:xs) (y:ys) = f x y : zipWithDefault d f xs ys
+
+isNode :: TricuAST -> Bool
+isNode t = case t of
+  TLeaf -> True
+  _     -> False
+
+isApp2 :: TricuAST -> Maybe (TricuAST, TricuAST)
+isApp2 (SApp a b) = Just (a, b)
+isApp2 _          = Nothing
+
+isKop :: TricuAST -> Bool
+isKop t = case isApp2 t of
+  Just (a,b) -> isNode a && isNode b
+  _          -> False
+
+-- detects the two canonical I-shapes in the tree calculus:
+--   △ (△ (△ △)) x    OR    △ (△ △ △) △
+isId :: TricuAST -> Bool
+isId t = case isApp2 t of
+  Just (ab, c) -> case isApp2 ab of
+    Just (a, b) | isNode a ->
+      case isApp2 b of
+        Just (b1, b2) ->
+          (isNode b1 && isKop b2) ||
+          (isKop b1 && isNode b2 && isNode c)
+        _ -> False
+    _ -> False
+  _ -> False
+
+-- head-True only, tail empty, and term is identity
+isId2 :: (Uses, TricuAST) -> Bool
+isId2 (True:[], t) = isId t
+isId2 _            = False
+
+-- Bulk helpers built from SKI (no new primitives)
+bPrime :: TricuAST
+bPrime = SApp _B _B                            -- B' = B B
+
+cPrime :: TricuAST
+cPrime = SApp (SApp _B (SApp _B _C)) _B        -- C' = B (B C) B
+
+sPrime :: TricuAST
+sPrime = SApp (SApp _B (SApp _B _S)) _B        -- S' = B (B S) B
+
+bulkB :: Int -> TricuAST
+bulkB n | n <= 1    = _B
+        | otherwise = SApp bPrime (bulkB (n - 1))
+
+bulkC :: Int -> TricuAST
+bulkC n | n <= 1    = _C
+        | otherwise = SApp cPrime (bulkC (n - 1))
+
+bulkS :: Int -> TricuAST
+bulkS n | n <= 1    = _S
+        | otherwise = SApp sPrime (bulkS (n - 1))
+
+-- Count how many leading pairs (a,b) repeat at the head of zip g1 g2
+headPairRun :: [Bool] -> [Bool] -> ((Bool, Bool), Int)
+headPairRun g1 g2 =
+  case zip g1 g2 of
+    []       -> ((False, False), 0)
+    (h:rest) -> (h, 1 + length (takeWhile (== h) rest))
+
+-- DB-native star_skibc_op_eta (adapted from strategies.mts), binder = level 0
+starSKIBCOpEtaDB :: DB -> TricuAST
+starSKIBCOpEtaDB t
+  | not (dependsOnLevel 0 t) = SApp _K (fromDBClosed t)
+starSKIBCOpEtaDB (BVar 0)     = _I
+starSKIBCOpEtaDB (BApp e1 e2)
+  -- if binder not in right: use C
+  | not (dependsOnLevel 0 e2)
+  = SApp (SApp _C (starSKIBCOpEtaDB e1)) (fromDBClosed e2)
+  -- if binder not in left:
+  | not (dependsOnLevel 0 e1)
+  = case e2 of
+      -- η case: \x. f x  ==>  f
+      BVar 0 -> fromDBClosed e1
+      _      -> SApp (SApp _B (fromDBClosed e1)) (starSKIBCOpEtaDB e2)
+  -- otherwise: S
+  | otherwise
+  = SApp (SApp _S (starSKIBCOpEtaDB e1)) (starSKIBCOpEtaDB e2)
+-- Structural nodes with binder underneath: fall back to plain SKI (rare)
+starSKIBCOpEtaDB other        = toSKIDB other
--- a/src/FileEval.hs
+++ b/src/FileEval.hs
@ -6,6 +6,7 @@ import Parser
 import Research

 import Data.List       (partition)
+import Data.Maybe      (mapMaybe)
 import Control.Monad   (foldM)
 import System.IO
 import System.FilePath (takeDirectory, normalise, (</>))
@ -13,6 +14,26 @@ import System.FilePath (takeDirectory, normalise, (</>))
 import qualified Data.Map as Map
 import qualified Data.Set as Set

+extractMain :: Env -> Either String T
+extractMain env =
+  case Map.lookup "main" env of
+    Just result -> Right result
+    Nothing -> Left "No `main` function detected"
+
+processImports :: Set.Set FilePath -> FilePath -> FilePath -> [TricuAST]
+                 -> Either String ([TricuAST], [(FilePath, String, FilePath)])
+processImports seen base currentPath asts =
+  let (imports, nonImports) = partition isImp asts
+      importPaths = mapMaybe getImportInfo imports
+  in if currentPath `Set.member` seen
+     then Left $ "Encountered cyclic import: " ++ currentPath
+     else Right (nonImports, importPaths)
+  where
+    isImp (SImport _ _) = True
+    isImp _ = False
+    getImportInfo (SImport p n) = Just (p, n, makeRelativeTo currentPath p)
+    getImportInfo _ = Nothing
+
 evaluateFileResult :: FilePath -> IO T
 evaluateFileResult filePath = do
  contents <- readFile filePath
@ -20,11 +41,11 @@ evaluateFileResult filePath = do
  case parseProgram tokens of
    Left err -> errorWithoutStackTrace (handleParseError err)
    Right ast -> do
-      ast <- preprocessFile filePath
-      let finalEnv = evalTricu Map.empty ast
-      case Map.lookup "main" finalEnv of
-        Just finalResult -> return finalResult
-        Nothing -> errorWithoutStackTrace "No `main` function detected"
+      processedAst <- preprocessFile filePath
+      let finalEnv = evalTricu Map.empty processedAst
+      case extractMain finalEnv of
+        Right result -> return result
+        Left err -> errorWithoutStackTrace err

 evaluateFile :: FilePath -> IO Env
 evaluateFile filePath = do
@ -50,38 +71,26 @@ preprocessFile :: FilePath -> IO [TricuAST]
 preprocessFile p = preprocessFile' Set.empty p p

 preprocessFile' :: Set.Set FilePath -> FilePath -> FilePath -> IO [TricuAST]
-preprocessFile' s b p
-  | p `Set.member` s =
-      errorWithoutStackTrace $ "Encountered cyclic import: " ++ p
-  | otherwise = do
-      c <- readFile p
-      let t = lexTricu c
-      case parseProgram t of
-        Left e -> errorWithoutStackTrace (handleParseError e)
-        Right a -> do
-          let (i, n) = partition isImp a
-          let s' = Set.insert p s
-          r <- concat <$>
-            mapM (procImp s' "" p) i
-          pure $ r ++ n
+preprocessFile' seen base currentPath = do
+  contents <- readFile currentPath
+  let tokens = lexTricu contents
+  case parseProgram tokens of
+    Left err -> errorWithoutStackTrace (handleParseError err)
+    Right ast ->
+      case processImports seen base currentPath ast of
+        Left err -> errorWithoutStackTrace err
+        Right (nonImports, importPaths) -> do
+          let seen' = Set.insert currentPath seen
+          imported <- concat <$> mapM (processImportPath seen' base) importPaths
+          pure $ imported ++ nonImports
  where
-    isImp :: TricuAST -> Bool
+    processImportPath seen base (path, name, importPath) = do
+      ast <- preprocessFile' seen base importPath
+      pure $ map (nsDefinition (if name == "!Local" then "" else name))
+           $ filter (not . isImp) ast
    isImp (SImport _ _) = True
    isImp _ = False

-    procImp :: Set.Set FilePath -> String -> FilePath -> TricuAST -> IO [TricuAST]
-    procImp s m f (SImport p "!Local") = do
-      let ip = makeRelativeTo f p
-      a <- preprocessFile' s b ip
-      let d = filter (not . isImp) a
-      pure $ map (nsDefinition m) d
-    procImp s _ f (SImport p n) = do
-      let ip = makeRelativeTo f p
-      a <- preprocessFile' s b ip
-      let d = filter (not . isImp) a
-      pure $ map (nsDefinition n) d
-    procImp _ _ _ _ = error "Unexpected non-import in processImport"
-
 makeRelativeTo :: FilePath -> FilePath -> FilePath
 makeRelativeTo f i =
    let d = takeDirectory f
--- a/src/Lexer.hs
+++ b/src/Lexer.hs
@ -3,6 +3,7 @@ module Lexer where
 import Research

 import Control.Monad               (void)
+import Data.Functor                (($>))
 import Data.Void
 import Text.Megaparsec
 import Text.Megaparsec.Char hiding (space)
@ -40,7 +41,6 @@ tricuLexer = do
      , try stringLiteral
      , assign
      , colon
-      , backslash
      , openParen
      , closeParen
      , openBracket
@ -54,7 +54,7 @@ lexTricu input = case runParser tricuLexer "" input of


 keywordT :: Lexer LToken
-keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT
+keywordT = string "t" *> notFollowedBy alphaNumChar $> LKeywordT

 identifier :: Lexer LToken
 identifier = do
@ -63,7 +63,7 @@ identifier = do
              <|> digitChar <|> char '_' <|> char '-' <|> char '?'
              <|> char '$'  <|> char '#' <|> char '@' <|> char '%'
  let name = first : rest
-  if (name == "t" || name == "!result")
+  if name == "t" || name == "!result"
    then fail "Keywords (`t`, `!result`) cannot be used as an identifier"
    else return (LIdentifier name)

@ -76,7 +76,7 @@ namespace = do
  return (LNamespace name)

 dot :: Lexer LToken
-dot = char '.' *> pure LDot
+dot = char '.' $> LDot

 lImport :: Lexer LToken
 lImport = do
@ -88,28 +88,25 @@ lImport = do
  return (LImport path name)

 assign :: Lexer LToken
-assign = char '=' *> pure LAssign
+assign = char '=' $> LAssign

 colon :: Lexer LToken
-colon = char ':' *> pure LColon
-
-backslash :: Lexer LToken
-backslash = char '\\' *> pure LBackslash
+colon = char ':' $> LColon

 openParen :: Lexer LToken
-openParen = char '(' *> pure LOpenParen
+openParen = char '(' $> LOpenParen

 closeParen :: Lexer LToken
-closeParen = char ')' *> pure LCloseParen
+closeParen = char ')' $> LCloseParen

 openBracket :: Lexer LToken
-openBracket = char '[' *> pure LOpenBracket
+openBracket = char '[' $> LOpenBracket

 closeBracket :: Lexer LToken
-closeBracket = char ']' *> pure LCloseBracket
+closeBracket = char ']' $> LCloseBracket

 lnewline :: Lexer LToken
-lnewline = char '\n' *> pure LNewline
+lnewline = char '\n' $> LNewline

 sc :: Lexer ()
 sc = space
@ -125,7 +122,22 @@ integerLiteral = do
 stringLiteral :: Lexer LToken
 stringLiteral = do
  char '"'
-  content <- many (noneOf ['"'])
-  char '"' --"
+  content <- manyTill Lexer.charLiteral (char '"')
  return (LStringLiteral content)

+charLiteral :: Lexer Char
+charLiteral = escapedChar <|> normalChar
+  where
+    normalChar = noneOf ['"', '\\']
+    escapedChar = do
+      void $ char '\\'
+      c <- oneOf ['n', 't', 'r', 'f', 'b', '\\', '"', '\'']
+      return $ case c of
+        'n'  -> '\n'
+        't'  -> '\t'
+        'r'  -> '\r'
+        'f'  -> '\f'
+        'b'  -> '\b'
+        '\\' -> '\\'
+        '"'  -> '"'
+        '\'' -> '\''
--- a/src/Main.hs
+++ b/src/Main.hs
@ -63,18 +63,17 @@ main = do
  case args of
    Repl -> do
      putStrLn "Welcome to the tricu REPL"
-      putStrLn "You can exit with `CTRL+D` or the `!exit` command.`"
+      putStrLn "You may exit with `CTRL+D` or the `!exit` command."
+      putStrLn "Try typing `!` with tab completion for more commands."
      repl Map.empty
    Evaluate { file = filePaths, form = form } -> do
      result <- case filePaths of
-        [] -> do
-          t <- getContents
-          pure $ runTricu t
+        [] -> runTricuT <$> getContents
        (filePath:restFilePaths) -> do
            initialEnv <- evaluateFile filePath
            finalEnv <- foldM evaluateFileWithContext initialEnv restFilePaths
            pure $ mainResult finalEnv
-      let fRes = formatResult form result
+      let fRes = formatT form result
      putStr fRes
    TDecode { file = filePaths } -> do
      value <- case filePaths of
@ -82,8 +81,48 @@ main = do
        (filePath:_) -> readFile filePath
      putStrLn $ decodeResult $ result $ evalTricu Map.empty $ parseTricu value

-runTricu :: String -> T
-runTricu input =
+-- Simple interfaces
+
+runTricu :: String -> String
+runTricu = formatT TreeCalculus . runTricuT
+
+runTricuT :: String -> T
+runTricuT input =
  let asts     = parseTricu input
      finalEnv = evalTricu Map.empty asts
   in result finalEnv
+
+runTricuEnv :: Env -> String -> String
+runTricuEnv env = formatT TreeCalculus . runTricuTEnv env
+
+runTricuTEnv :: Env -> String -> T
+runTricuTEnv env input =
+  let asts     = parseTricu input
+      finalEnv = evalTricu env asts
+   in result finalEnv
+
+runTricuWithEnvT :: String -> (Env, T)
+runTricuWithEnvT input =
+  let asts     = parseTricu input
+      finalEnv = evalTricu Map.empty asts
+   in (finalEnv, result finalEnv)
+
+runTricuWithEnv :: String -> (Env, String)
+runTricuWithEnv input =
+  let asts     = parseTricu input
+      finalEnv = evalTricu Map.empty asts
+      res      = result finalEnv
+   in (finalEnv, formatT TreeCalculus res)
+
+runTricuEnvWithEnvT :: Env -> String -> (Env, T)
+runTricuEnvWithEnvT env input =
+  let asts     = parseTricu input
+      finalEnv = evalTricu env asts
+   in (finalEnv, result finalEnv)
+
+runTricuEnvWithEnv :: Env -> String -> (Env, String)
+runTricuEnvWithEnv env input =
+  let asts     = parseTricu input
+      finalEnv = evalTricu env asts
+      res      = result finalEnv
+   in (finalEnv, formatT TreeCalculus res)
--- a/src/Parser.hs
+++ b/src/Parser.hs
@ -130,7 +130,6 @@ parseFunctionM = do
 parseLambdaM :: ParserM TricuAST
 parseLambdaM = do
  let ident = (\case LIdentifier _ -> True; _ -> False)
-  _      <- satisfyM (== LBackslash)
  params <- some (satisfyM ident)
  _      <- satisfyM (== LColon)
  scnParserM
@ -145,11 +144,11 @@ parseLambdaExpressionM = choice

 parseAtomicLambdaM :: ParserM TricuAST
 parseAtomicLambdaM = choice
-  [ parseVarM
+  [ try parseLambdaM
+  , parseVarM
  , parseTreeLeafM
  , parseLiteralM
  , parseListLiteralM
-  , try parseLambdaM
  , between (satisfyM (== LOpenParen)) (satisfyM (== LCloseParen)) parseLambdaExpressionM
  ]

@ -205,7 +204,8 @@ parseTreeLeafOrParenthesizedM = choice

 parseAtomicM :: ParserM TricuAST
 parseAtomicM = choice
-  [ parseVarM
+  [ try parseLambdaM
+  , parseVarM
  , parseTreeLeafM
  , parseListLiteralM
  , parseGroupedM
--- a/src/REPL.hs
+++ b/src/REPL.hs
@ -6,68 +6,153 @@ import Lexer
 import Parser
 import Research

-import Control.Exception      (SomeException, catch)
-import Control.Monad.IO.Class (liftIO)
+import Control.Exception         (IOException, SomeException, catch
+                                 , displayException)
+import Control.Monad             (forM_)
 import Control.Monad.Catch       (handle, MonadCatch)
-import Data.Char              (isSpace)
-import Data.List              ( dropWhile
-                              , dropWhileEnd
-                              , intercalate
-                              , isPrefixOf)
+import Control.Monad.IO.Class    (liftIO)
+import Control.Monad.Trans.Class (lift)
+import Control.Monad.Trans.Maybe (MaybeT(..), runMaybeT)
+import Data.Char                 (isSpace, isUpper)
+import Data.List                 (dropWhile, dropWhileEnd, isPrefixOf)
+import Data.Version (showVersion)
+import Paths_tricu (version)
 import System.Console.Haskeline

 import qualified Data.Map as Map
+import qualified Data.Text as T
+import qualified Data.Text.IO as T

 repl :: Env -> IO ()
-repl env = runInputT defaultSettings (withInterrupt (loop env True))
+repl env = runInputT settings (withInterrupt (loop env Decode))
  where
-    loop :: Env -> Bool -> InputT IO ()
-    loop env decode = handle (interruptHandler env decode) $ do
+    settings :: Settings IO
+    settings = Settings
+      { complete = completeWord Nothing " \t" completeCommands
+      , historyFile = Just "~/.local/state/tricu/history"
+      , autoAddHistory = True
+      }
+
+    completeCommands :: String -> IO [Completion]
+    completeCommands str = return $ map simpleCompletion $
+      filter (str `isPrefixOf`) commands
+      where
+        commands = [ "!exit"
+                   , "!output"
+                   , "!definitions"
+                   , "!import"
+                   , "!clear"
+                   , "!save"
+                   , "!reset"
+                   , "!version"
+                   ]
+
+    loop :: Env -> EvaluatedForm -> InputT IO ()
+    loop env form = handle (interruptHandler env form) $ do
      minput <- getInputLine "tricu < "
      case minput of
        Nothing -> outputStrLn "Exiting tricu"
        Just s
-          | strip s == "" -> loop env decode
+          | strip s == "" -> loop env form
          | strip s == "!exit" -> outputStrLn "Exiting tricu"
-          | strip s == "!decode" -> do
-              outputStrLn $ "Decoding " ++ (if decode then "disabled" else "enabled")
-              loop env (not decode)
-          | "!import" `isPrefixOf` strip s -> do
-              let afterImport = dropWhile (== ' ') $ drop (length ("!import" :: String)) (strip s)
-              if not (null afterImport)
-                then outputStrLn "Warning: REPL imports are interactive; \
-                                  \additional arguments are ignored."
-                else pure ()
-              path <- getInputLine "File path to load < "
-              case path of
-                Nothing -> do
-                  outputStrLn "No input received; stopping import."
-                  loop env decode
-                Just p -> do
-                  loadedEnv <- liftIO $ evaluateFileWithContext env
-                    (strip p) `catch` \e -> errorHandler env e
-                  loop (Map.delete "!result" (Map.union loadedEnv env)) decode
-          | take 2 s == "--" -> loop env decode
+          | strip s == "!clear" -> do
+              liftIO $ putStr "\ESC[2J\ESC[H"
+              loop env form
+          | strip s == "!reset" -> do
+              outputStrLn "Environment reset to initial state"
+              loop Map.empty form
+          | strip s == "!version" -> do
+              outputStrLn $ "tricu version " ++ showVersion version
+              loop env form
+          | "!save" `isPrefixOf` strip s -> handleSave env form
+          | strip s == "!output" -> handleOutput env form
+          | strip s == "!definitions" -> do
+              let defs = Map.keys $ Map.delete "!result" env
+              if null defs
+                then outputStrLn "No definitions discovered."
+                else do
+                  outputStrLn "Available definitions:"
+                  mapM_ outputStrLn defs
+              loop env form
+          | "!import" `isPrefixOf` strip s -> handleImport env form
+          | take 2 s == "--" -> loop env form
          | otherwise -> do
-              newEnv <- liftIO $ processInput env s decode `catch` errorHandler env
-              loop newEnv decode
+              newEnv <- liftIO $ processInput env s form `catch` errorHandler env
+              loop newEnv form

-    interruptHandler :: Env -> Bool -> Interrupt -> InputT IO ()
-    interruptHandler env decode _ = do
+    handleOutput :: Env -> EvaluatedForm -> InputT IO ()
+    handleOutput env currentForm = do
+      let formats = [Decode, TreeCalculus, FSL, AST, Ternary, Ascii]
+      outputStrLn "Available output formats:"
+      mapM_ (\(i, f) -> outputStrLn $ show i ++ ". " ++ show f)
+        (zip [1..] formats)
+
+      result <- runMaybeT $ do
+        input <- MaybeT $ getInputLine "Select output format (1-6) < "
+        case reads input of
+          [(n, "")] | n >= 1 && n <= 6 ->
+            return $ formats !! (n-1)
+          _ -> MaybeT $ return Nothing
+
+      case result of
+        Nothing -> do
+          outputStrLn "Invalid selection. Keeping current output format."
+          loop env currentForm
+        Just newForm -> do
+          outputStrLn $ "Output format changed to: " ++ show newForm
+          loop env newForm
+
+    handleImport :: Env -> EvaluatedForm -> InputT IO ()
+    handleImport env form = do
+      res <- runMaybeT $ do
+        let fset = setComplete completeFilename defaultSettings
+        path <- MaybeT $ runInputT fset $
+          getInputLineWithInitial "File path to load < " ("", "")
+
+        text <- MaybeT $ liftIO $ handle (\e -> do
+            putStrLn $ "Error reading file: " ++ displayException (e :: IOException)
+            return Nothing
+          ) $ Just <$> readFile (strip path)
+
+        case parseProgram (lexTricu text) of
+          Left err -> do
+            lift $ outputStrLn $ "Parse error: " ++ handleParseError err
+            MaybeT $ return Nothing
+          Right ast -> do
+            ns <- MaybeT $ runInputT defaultSettings $
+              getInputLineWithInitial "Namespace (or !Local for no namespace) < " ("", "")
+
+            let name = strip ns
+            if (name /= "!Local" && (null name || not (isUpper (head name)))) then do
+                lift $ outputStrLn "Namespace must start with an uppercase letter"
+                MaybeT $ return Nothing
+            else do
+                prog <- liftIO $ preprocessFile (strip path)
+                let code = case name of
+                      "!Local" -> prog
+                      _ -> nsDefinitions name prog
+                    env' = evalTricu env code
+                return env'
+      case res of
+        Nothing -> do
+          outputStrLn "Import cancelled"
+          loop env form
+        Just env' ->
+          loop (Map.delete "!result" env') form
+
+    interruptHandler :: Env -> EvaluatedForm -> Interrupt -> InputT IO ()
+    interruptHandler env form _ = do
      outputStrLn "Interrupted with CTRL+C\n\
                  \You can use the !exit command or CTRL+D to exit"
-      loop env decode
+      loop env form

-    processInput :: Env -> String -> Bool -> IO Env
-    processInput env input decode = do
+    processInput :: Env -> String -> EvaluatedForm -> IO Env
+    processInput env input form = do
      let asts   = parseTricu input
          newEnv = evalTricu env asts
      case Map.lookup "!result" newEnv of
        Just r -> do
-          putStrLn $ "tricu > " ++ 
-            if decode 
-              then decodeResult r
-              else show r
+          putStrLn $ "tricu > " ++ formatT form r
        Nothing -> pure ()
      return newEnv

@ -78,3 +163,28 @@ repl env = runInputT defaultSettings (withInterrupt (loop env True))

    strip :: String -> String
    strip = dropWhileEnd isSpace . dropWhile isSpace
+
+    handleSave :: Env -> EvaluatedForm -> InputT IO ()
+    handleSave env form = do
+      let fset = setComplete completeFilename defaultSettings
+      path <- runInputT fset $
+        getInputLineWithInitial "File to save < " ("", "")
+
+      case path of
+        Nothing -> do
+          outputStrLn "Save cancelled"
+          loop env form
+        Just p -> do
+          let definitions = Map.toList $ Map.delete "!result" env
+              filepath = strip p
+
+          outputStrLn "Starting save..."
+          liftIO $ writeFile filepath ""
+          outputStrLn "File created..."
+          forM_ definitions $ \(name, value) -> do
+            let content = name ++ " = " ++ formatT TreeCalculus value ++ "\n"
+            outputStrLn $ "Writing definition: " ++ name ++ " with length " ++ show (length content)
+            liftIO $ appendFile filepath content
+          outputStrLn $ "Saved " ++ show (length definitions) ++ " definitions to " ++ p
+
+          loop env form
--- a/src/Research.hs
+++ b/src/Research.hs
@ -1,6 +1,5 @@
 module Research where

-import Control.Monad.State
 import Data.List                 (intercalate)
 import Data.Map                  (Map)
 import Data.Text                 (Text, replace)
@ -16,7 +15,7 @@ data T = Leaf | Stem T | Fork T T
 -- Abstract Syntax Tree for tricu
 data TricuAST
  = SVar String
-  | SInt Int
+  | SInt Integer
  | SStr String
  | SList [TricuAST]
  | SDef String [String] TricuAST
@ -34,12 +33,11 @@ data LToken
  = LKeywordT
  | LIdentifier String
  | LNamespace String
-  | LIntegerLiteral Int
+  | LIntegerLiteral Integer
  | LStringLiteral String
  | LAssign
  | LColon
  | LDot
-  | LBackslash
  | LOpenParen
  | LCloseParen
  | LOpenBracket
@ -55,15 +53,24 @@ data EvaluatedForm = TreeCalculus | FSL | AST | Ternary | Ascii | Decode
 -- Environment containing previously evaluated TC terms
 type Env = Map.Map String T

-- Tree Calculus Reduction
+-- Tree Calculus Reduction Rules
+{- 
+  The t operator is left associative.
+  1.  t  t      a b       -> a
+  2.  t (t a)   b c       -> a c (b c)
+  3a. t (t a b) c t       -> a
+  3b. t (t a b) c (t u)   -> b u
+  3c. t (t a b) c (t u v) -> c u v
+-}
 apply :: T -> T -> T
+apply (Fork Leaf a)         _         = a
+apply (Fork (Stem a) b) c             = apply (apply a c) (apply b c)
+apply (Fork (Fork a  b) c)  Leaf      = a
+apply (Fork (Fork a  b) c) (Stem u)   = apply b u
+apply (Fork (Fork a  b) c) (Fork u v) = apply (apply c u) v
+-- Left associative `t`
 apply  Leaf b                         = Stem b
 apply (Stem a) b                      = Fork a b
-apply (Fork Leaf a) _                   = a
-apply (Fork (Stem a1) a2) b             = apply (apply a1 b) (apply a2 b)
-apply (Fork (Fork a1 a2) a3) Leaf       = a1
-apply (Fork (Fork a1 a2) a3) (Stem u)   = apply a2 u
-apply (Fork (Fork a1 a2) a3) (Fork u v) = apply (apply a3 u) v

 -- Booleans
 _false :: T
@ -77,9 +84,9 @@ _not = Fork (Fork _true (Fork Leaf _false)) Leaf

 -- Marshalling
 ofString :: String -> T
-ofString str = ofList (map ofNumber (map fromEnum str))
+ofString str = ofList $ map (ofNumber . toInteger . fromEnum) str

-ofNumber :: Int -> T
+ofNumber :: Integer -> T
 ofNumber 0 = Leaf
 ofNumber n =
  Fork
@ -87,10 +94,9 @@ ofNumber n =
    (ofNumber (n `div` 2))

 ofList :: [T] -> T
-ofList [] = Leaf
-ofList (x:xs) = Fork x (ofList xs)
+ofList = foldr Fork Leaf

-toNumber :: T -> Either String Int
+toNumber :: T -> Either String Integer
 toNumber Leaf = Right 0
 toNumber (Fork Leaf rest) = case toNumber rest of
  Right n -> Right (2 * n)
@ -102,7 +108,7 @@ toNumber _ = Left "Invalid Tree Calculus number"

 toString :: T -> Either String String
 toString tc = case toList tc of
-  Right list -> traverse (fmap toEnum . toNumber) list
+  Right list -> traverse (fmap (toEnum . fromInteger) . toNumber) list
  Left err -> Left "Invalid Tree Calculus string"

 toList :: T -> Either String [T]
@ -113,20 +119,20 @@ toList (Fork x rest) = case toList rest of
 toList _ = Left "Invalid Tree Calculus list"

 -- Outputs
-formatResult :: EvaluatedForm -> T -> String
-formatResult TreeCalculus = toSimpleT . show
-formatResult FSL          = show
-formatResult AST          = show . toAST
-formatResult Ternary      = toTernaryString
-formatResult Ascii        = toAscii
-formatResult Decode       = decodeResult
+formatT :: EvaluatedForm -> T -> String
+formatT TreeCalculus = toSimpleT . show
+formatT FSL          = show
+formatT AST          = show . toAST
+formatT Ternary      = toTernaryString
+formatT Ascii        = toAscii
+formatT Decode       = decodeResult

 toSimpleT :: String -> String
 toSimpleT s = T.unpack
  $ replace "Fork" "t"
  $ replace "Stem" "t"
  $ replace "Leaf" "t"
-  $ (T.pack s)
+  $ T.pack s

 toTernaryString :: T -> String
 toTernaryString Leaf = "0"
@ -153,8 +159,18 @@ toAscii tree = go tree "" True
        ++ go right (prefix ++ (if isLast then "    " else "|   ")) True

 decodeResult :: T -> String
-decodeResult tc
-  | Right num  <- toNumber tc = show num
-  | Right str  <- toString tc = "\"" ++ str ++ "\""
-  | Right list <- toList tc   = "[" ++ intercalate ", " (map decodeResult list) ++ "]"
-  | otherwise                 = formatResult TreeCalculus tc
+decodeResult Leaf = "t"
+decodeResult tc =
+  case (toString tc, toList tc, toNumber tc) of
+    (Right s, _, _) | all isCommonChar s -> "\"" ++ s ++ "\""
+    (_, _, Right n) -> show n
+    (_, Right xs@(_:_), _) -> "[" ++ intercalate ", " (map decodeResult xs) ++ "]"
+    (_, Right [], _) -> "[]"
+    _ -> formatT TreeCalculus tc
+  where
+    isCommonChar c =
+      let n = fromEnum c
+      in (n >= 32 && n <= 126)
+         || n == 9
+         || n == 10
+         || n == 13
--- a/test/Spec.hs
+++ b/test/Spec.hs
@ -21,8 +21,8 @@ import qualified Data.Set as Set
 main :: IO ()
 main = defaultMain tests

-runTricu :: String -> String
-runTricu s = show $ result (evalTricu Map.empty $ parseTricu s)
+tricuTestString :: String -> String
+tricuTestString s = show $ result (evalTricu Map.empty $ parseTricu s)

 tests :: TestTree
 tests = testGroup "Tricu Tests"
@ -34,6 +34,9 @@ tests = testGroup "Tricu Tests"
  , fileEval
  , modules
  , demos
+  , decoding
+	, elimLambdaSingle
+	, stressElimLambda
  ]

 lexer :: TestTree
@ -50,7 +53,22 @@ lexer = testGroup "Lexer Tests"

  , testCase "Lex escaped characters in strings" $ do
      let input = "\"hello\\nworld\""
-          expect = Right [LStringLiteral "hello\\nworld"]
+          expect = Right [LStringLiteral "hello\nworld"]
+      runParser tricuLexer "" input @?= expect
+
+  , testCase "Lex multiple escaped characters in strings" $ do
+      let input = "\"tab:\\t newline:\\n quote:\\\" backslash:\\\\\""
+          expect = Right [LStringLiteral "tab:\t newline:\n quote:\" backslash:\\"]
+      runParser tricuLexer "" input @?= expect
+
+  , testCase "Lex escaped characters in string literals" $ do
+      let input = "x = \"line1\\nline2\\tindented\""
+          expect = Right [LIdentifier "x", LAssign, LStringLiteral "line1\nline2\tindented"]
+      runParser tricuLexer "" input @?= expect
+
+  , testCase "Lex empty string with escape sequence" $ do
+      let input = "\"\\\"\""
+          expect = Right [LStringLiteral "\""]
      runParser tricuLexer "" input @?= expect

  , testCase "Lex mixed literals" $ do
@ -86,7 +104,7 @@ parser = testGroup "Parser Tests"
        Right _ -> assertFailure "Expected failure when trying to assign the value of T"

  , testCase "Parse function definitions" $ do
-      let input = "x = (\\a b c : a)"
+      let input = "x = (a b c : a)"
          expect = SDef "x" [] (SLambda ["a"] (SLambda ["b"] (SLambda ["c"] (SVar "a"))))
      parseSingle input @?= expect

@ -106,7 +124,7 @@ parser = testGroup "Parser Tests"
      parseSingle input @?= expect

  , testCase "Parse function with applications" $ do
-      let input  = "f = (\\x : t x)"
+      let input  = "f = (x : t x)"
          expect = SDef "f" [] (SLambda ["x"] (SApp TLeaf (SVar "x")))
      parseSingle input @?= expect

@ -148,22 +166,22 @@ parser = testGroup "Parser Tests"
      parseSingle input @?= expect

  , testCase "Parse nested parentheses in function body" $ do
-      let input  = "f = (\\x : t (t (t t)))"
+      let input  = "f = (x : t (t (t t)))"
          expect = SDef "f" [] (SLambda ["x"] (SApp TLeaf (SApp TLeaf (SApp TLeaf TLeaf))))
      parseSingle input @?= expect

  , testCase "Parse lambda abstractions" $ do
-      let input  = "(\\a : a)"
+      let input  = "(a : a)"
          expect = (SLambda ["a"] (SVar "a"))
      parseSingle input @?= expect

  , testCase "Parse multiple arguments to lambda abstractions" $ do
-      let input  = "x = (\\a b : a)"
+      let input  = "x = (a b : a)"
          expect = SDef "x" [] (SLambda ["a"] (SLambda ["b"] (SVar "a")))
      parseSingle input @?= expect

  , testCase "Grouping T terms with parentheses in function application" $ do
-      let input  = "x = (\\a : a)\nx (t)"
+      let input  = "x = (a : a)\nx (t)"
          expect = [SDef "x" [] (SLambda ["a"] (SVar "a")),SApp (SVar "x") TLeaf]
      parseTricu input @?= expect

@ -250,7 +268,7 @@ simpleEvaluation = testGroup "Evaluation Tests"
  , testCase "Immutable definitions" $ do
      let input = "x = t t\nx = t\nx"
          env = evalTricu Map.empty (parseTricu input)
-      result <- try (evaluate (runTricu input)) :: IO (Either SomeException String)
+      result <- try (evaluate (tricuTestString input)) :: IO (Either SomeException String)
      case result of
        Left  _ -> return ()
        Right _ -> assertFailure "Expected evaluation error"
@ -258,7 +276,7 @@ simpleEvaluation = testGroup "Evaluation Tests"

  , testCase "Apply identity to Boolean Not" $ do
      let not = "(t (t (t t) (t t t)) t)"
-      let input = "x = (\\a : a)\nx " ++ not
+      let input = "x = (a : a)\nx " ++ not
          env = evalTricu Map.empty (parseTricu input)
      result env @?= Fork (Fork (Stem Leaf) (Fork Leaf Leaf)) Leaf
  ]
@ -266,81 +284,85 @@ simpleEvaluation = testGroup "Evaluation Tests"
 lambdas :: TestTree
 lambdas = testGroup "Lambda Evaluation Tests"
  [ testCase "Lambda Identity Function" $ do
-      let input = "id = (\\x : x)\nid t"
-      runTricu input @?= "Leaf"
+      let input = "id = (x : x)\nid t"
+      tricuTestString input @?= "Leaf"

  , testCase "Lambda Constant Function (K combinator)" $ do
-      let input = "k = (\\x y : x)\nk t (t t)"
-      runTricu input @?= "Leaf"
+      let input = "k = (x y : x)\nk t (t t)"
+      tricuTestString input @?= "Leaf"

  , testCase "Lambda Application with Variable" $ do
-      let input = "id = (\\x : x)\nval = t t\nid val"
-      runTricu input @?= "Stem Leaf"
+      let input = "id = (x : x)\nval = t t\nid val"
+      tricuTestString input @?= "Stem Leaf"

  , testCase "Lambda Application with Multiple Arguments" $ do
-      let input = "apply = (\\f x y : f x y)\nk = (\\a b : a)\napply k t (t t)"
-      runTricu input @?= "Leaf"
+      let input = "apply = (f x y : f x y)\nk = (a b : a)\napply k t (t t)"
+      tricuTestString input @?= "Leaf"

   , testCase "Nested Lambda Application" $ do
-      let input = "apply = (\\f x y : f x y)\nid = (\\x : x)\napply (\\f x : f x) id t"
-      runTricu input @?= "Leaf"
+      let input = "apply = (f x y : f x y)\nid = (x : x)\napply (f x : f x) id t"
+      tricuTestString input @?= "Leaf"

  , testCase "Lambda with a complex body" $ do
-      let input = "f = (\\x : t (t x))\nf t"
-      runTricu input @?= "Stem (Stem Leaf)"
+      let input = "f = (x : t (t x))\nf t"
+      tricuTestString input @?= "Stem (Stem Leaf)"

  , testCase "Lambda returning a function" $ do
-      let input = "f = (\\x : (\\y : x))\ng = f t\ng (t t)"
-      runTricu input @?= "Leaf"
+      let input = "f = (x : (y : x))\ng = f t\ng (t t)"
+      tricuTestString input @?= "Leaf"

  , testCase "Lambda with Shadowing" $ do
-      let input = "f = (\\x : (\\x : x))\nf t (t t)"
-      runTricu input @?= "Stem Leaf"
+      let input = "f = (x : (x : x))\nf t (t t)"
+      tricuTestString input @?= "Stem Leaf"

   , testCase "Lambda returning another lambda" $ do
-      let input = "k = (\\x : (\\y : x))\nk_app = k t\nk_app (t t)"
-      runTricu input @?= "Leaf"
+      let input = "k = (x : (y : x))\nk_app = k t\nk_app (t t)"
+      tricuTestString input @?= "Leaf"

   , testCase "Lambda with free variables" $ do
-      let input = "y = t t\nf = (\\x : y)\nf t"
-      runTricu input @?= "Stem Leaf"
+      let input = "y = t t\nf = (x : y)\nf t"
+      tricuTestString input @?= "Stem Leaf"

   , testCase "SKI Composition" $ do
-      let input = "s = (\\x y z : x z (y z))\nk = (\\x y : x)\ni = (\\x : x)\ncomp = s k i\ncomp t (t t)"
-      runTricu input @?= "Stem (Stem Leaf)"
+      let input = "s = (x y z : x z (y z))\nk = (x y : x)\ni = (x : x)\ncomp = s k i\ncomp t (t t)"
+      tricuTestString input @?= "Stem (Stem Leaf)"

   , testCase "Lambda with multiple parameters and application" $ do
-      let input = "f = (\\a b c : t a b c)\nf t (t t) (t t t)"
-      runTricu input @?= "Stem Leaf"
+      let input = "f = (a b c : t a b c)\nf t (t t) (t t t)"
+      tricuTestString input @?= "Stem Leaf"

   , testCase "Lambda with nested application in the body" $ do
-      let input = "f = (\\x : t (t (t x)))\nf t"
-      runTricu input @?= "Stem (Stem (Stem Leaf))"
+      let input = "f = (x : t (t (t x)))\nf t"
+      tricuTestString input @?= "Stem (Stem (Stem Leaf))"

    , testCase "Lambda returning a function and applying it" $ do
-        let input = "f = (\\x : (\\y : t x y))\ng = f t\ng (t t)"
-        runTricu input @?= "Fork Leaf (Stem Leaf)"
+        let input = "f = (x : (y : t x y))\ng = f t\ng (t t)"
+        tricuTestString input @?= "Fork Leaf (Stem Leaf)"

    , testCase "Lambda applying a variable" $ do
-        let input = "id = (\\x : x)\na = t t\nid a"
-        runTricu input @?= "Stem Leaf"
+        let input = "id = (x : x)\na = t t\nid a"
+        tricuTestString input @?= "Stem Leaf"

    , testCase "Nested lambda abstractions in the same expression" $ do
-        let input = "f = (\\x : (\\y : x y))\ng = (\\z : z)\nf g t"
-        runTricu input @?= "Leaf"
+        let input = "f = (x : (y : x y))\ng = (z : z)\nf g t"
+        tricuTestString input @?= "Leaf"

-  , testCase "Lambda with a string literal" $ do
-        let input = "f = (\\x : x)\nf \"hello\""
-        runTricu input @?= "Fork (Fork Leaf (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) Leaf))))"
+  , testCase "Lambda applied to string literal" $ do
+        let input = "f = (x : x)\nf \"hello\""
+        tricuTestString input @?= "Fork (Fork Leaf (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork Leaf (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) (Fork (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork (Stem Leaf) Leaf))))))) Leaf))))"


-   , testCase "Lambda with an integer literal" $ do
-        let input = "f = (\\x : x)\nf 42"
-        runTricu input @?= "Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) Leaf)))))"
+   , testCase "Lambda applied to integer literal" $ do
+        let input = "f = (x : x)\nf 42"
+        tricuTestString input @?= "Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) (Fork Leaf (Fork (Stem Leaf) Leaf)))))"

-   , testCase "Lambda with a list literal" $ do
-        let input = "f = (\\x : x)\nf [t (t t)]"
-        runTricu input @?= "Fork Leaf (Fork (Stem Leaf) Leaf)"
+   , testCase "Lambda applied to list literal" $ do
+        let input = "f = (x : x)\nf [t (t t)]"
+        tricuTestString input @?= "Fork Leaf (Fork (Stem Leaf) Leaf)"
+
+  , testCase "Lambda containing list literal" $ do
+      let input = "(a : [(a)]) 1"
+      tricuTestString input @?= "Fork (Fork (Stem Leaf) Leaf) Leaf"
  ]

 providedLibraries :: TestTree
@ -414,7 +436,7 @@ providedLibraries = testGroup "Library Tests"

  , testCase "List map" $ do
      library <- evaluateFile "./lib/list.tri"
-      let input = "head (tail (map (\\a : (t t t)) [(t) (t) (t)]))"
+      let input = "head (tail (map (a : (t t t)) [(t) (t) (t)]))"
          env = evalTricu library (parseTricu input)
      result env @?= Fork Leaf Leaf

@ -513,8 +535,109 @@ demos = testGroup "Test provided demo functionality"
      decodeResult res @?= "\"(t (t (t t) (t t t)) (t t (t t t)))\""
  , testCase "Determining the size of functions" $ do
      res     <- liftIO $ evaluateFileResult "./demos/size.tri"
-      decodeResult res @?= "454"
+      decodeResult res @?= "321"
  , testCase "Level Order Traversal demo" $ do
      res     <- liftIO $ evaluateFileResult "./demos/levelOrderTraversal.tri"
      decodeResult res @?= "\"\n1 \n2 3 \n4 5 6 7 \n8 11 10 9 12 \""
  ]
+
+decoding :: TestTree
+decoding = testGroup "Decoding Tests"
+  [ testCase "Decode Leaf" $ do
+      decodeResult Leaf @?= "t"
+
+  , testCase "Decode list of non-ASCII numbers" $ do
+      let input = ofList [ofNumber 1, ofNumber 14, ofNumber 6]
+      decodeResult input @?= "[1, 14, 6]"
+
+  , testCase "Decode list of ASCII numbers as a string" $ do
+      let input = ofList [ofNumber 97, ofNumber 98, ofNumber 99]
+      decodeResult input @?= "\"abc\""
+
+  , testCase "Decode small number" $ do
+      decodeResult (ofNumber 42) @?= "42"
+
+  , testCase "Decode large number" $ do
+      decodeResult (ofNumber 9999) @?= "9999"
+
+  , testCase "Decode string in list" $ do
+      let input = ofList [ofString "hello", ofString "world"]
+      decodeResult input @?= "[\"hello\", \"world\"]"
+
+  , testCase "Decode mixed list with strings" $ do
+      let input = ofList [ofString "hello", ofNumber 42, ofString "world"]
+      decodeResult input @?= "[\"hello\", 42, \"world\"]"
+
+  , testCase "Decode nested lists with strings" $ do
+      let input = ofList [ofList [ofString "nested"], ofString "string"]
+      decodeResult input @?= "[[\"nested\"], \"string\"]"
+  ]
+
+elimLambdaSingle :: TestTree
+elimLambdaSingle = testCase "elimLambda preserves eval, fires eta, and SDef binds" $ do
+  -- 1) eta reduction, purely structural and parsed from source
+  let [etaIn] = parseTricu "x : f x"
+      [fRef ] = parseTricu "f"
+  elimLambda etaIn @?= fRef
+
+  -- 2) SDef binds its own name and parameters
+  let [defFXY] = parseTricu "f x y : f x"
+      fv       = freeVars defFXY
+  assertBool "f should be bound in SDef" ("f" `Set.notMember` fv)
+  assertBool "x should be bound in SDef" ("x" `Set.notMember` fv)
+  assertBool "y should be bound in SDef" ("y" `Set.notMember` fv)
+
+  -- 3) semantics preserved on a small program that exercises compose and triage
+  let src =
+        unlines
+          [ "false = t"
+          , "_     = t"
+          , "true  = t t"
+          , "id    = a : a"
+          , "const = a b : a"
+          , "compose = f g x : f (g x)"
+          , "triage = leaf stem fork : t (t leaf stem) fork"
+          , "test   = triage \"Leaf\" (_ : \"Stem\") (_ _ : \"Fork\")"
+          , "main   = compose id id test"
+          ]
+      prog        = parseTricu src
+      progElim    = map elimLambda prog
+      evalBefore  = result (evalTricu Map.empty prog)
+      evalAfter   = result (evalTricu Map.empty progElim)
+  evalAfter @?= evalBefore
+
+stressElimLambda :: TestTree
+stressElimLambda = testCase "stress elimLambda on wide list under deep curried lambda" $ do
+  let numVars = 200
+      numBody = 800
+      vars    = [ "x" ++ show i | i <- [1..numVars] ]
+      body    = "(" ++ unwords (replicate numBody "t") ++ ")"
+      etaOne  = "h : f h"
+      etaTwo  = "k : id k"
+      defId   = "id = a : a"
+      lambda  = unwords vars ++ " : " ++ body
+      src     = unlines
+                  [ defId
+                  , etaOne
+                  , "compose = f g x : f (g x)"
+                  , "f = t t"
+                  , etaTwo
+                  , lambda
+                  , "main = compose id id (" ++ head vars ++ " : f " ++ head vars ++ ")"
+                  ]
+      prog    = parseTricu src
+
+  let out = map elimLambda prog
+  let noLambda term = case term of
+        SLambda _ _ -> False
+        SApp f g    -> noLambda f && noLambda g
+        SList xs    -> all noLambda xs
+        TFork l r   -> noLambda l && noLambda r
+        TStem u     -> noLambda u
+        _           -> True
+
+  assertBool "all lambdas eliminated" (all noLambda out)
+
+  let before = result (evalTricu Map.empty prog)
+      after  = result (evalTricu Map.empty out)
+  after @?= before
--- a/test/comments-1.tri
+++ b/test/comments-1.tri
@ -1,9 +1,9 @@
 -- This is a tricu comment!
 -- t (t t) (t (t t t))
 -- t (t t t) (t t)
-- x = (\a : a)
+-- x = (a : a)
 main = t (t t) t -- Fork (Stem Leaf) Leaf
 -- t t
 -- x
-- x = (\a : a)
+-- x = (a : a)
 -- t
--- a/test/lambda-A.tri
+++ b/test/lambda-A.tri
@ -1 +1 @@
-main = (\x : x) t
+main = (x : x) t
--- a/test/map.tri
+++ b/test/map.tri
@ -1,2 +1,2 @@
-x = map (\i : append "Successfully concatenated " i) [("two strings!")]
+x = map (i : append "Successfully concatenated " i) [("two strings!")]
 main = equal? x [("Successfully concatenated two strings!")]
--- a/test/size.tri
+++ b/test/size.tri
@ -1,21 +1,21 @@
-compose = \f g x : f (g x)
+compose = f g x : f (g x)

-succ = y (\self :
+succ = y (self :
  triage
    1
    t
    (triage
      (t (t t))
-      (\_ tail : t t (self tail))
+      (_ tail : t t (self tail))
      t))

-size = (\x :
-  (y (\self x :
+size = (x :
+  (y (self x :
    compose succ
      (triage
-        (\x : x)
+        (x : x)
        self
-        (\x y : compose (self x) (self y))
+        (x y : compose (self x) (self y))
        x)) x 0))

 size size
--- a/test/string.tri
+++ b/test/string.tri
@ -1 +1 @@
-head (map (\i : append "String " i) [("test!")])
+head (map (i : append "String " i) [("test!")])
--- a/test/vars-B.tri
+++ b/test/vars-B.tri
@ -1 +1 @@
-y = \x : x
+y = x : x
--- a/tricu.cabal
+++ b/tricu.cabal
@ -1,7 +1,7 @@
 cabal-version: 1.12

 name:           tricu
-version:        0.14.0
+version:        0.19.0
 description:    A micro-language for exploring Tree Calculus
 author:         James Eversole
 maintainer:     james@eversole.co
@ -32,6 +32,7 @@ executable tricu
    , megaparsec
    , mtl
    , text
+    , transformers
  other-modules:
    Eval
    FileEval
@ -63,6 +64,7 @@ test-suite tricu-tests
    , tasty-hunit
    , tasty-quickcheck
    , text
+    , transformers
  default-language:    Haskell2010
  other-modules:
    Eval
Author	SHA1	Message	Date
James Eversole	0cdc0bfc34	"size" function nodes down from 454 to 321	2025-08-07 20:08:59 -05:00
James Eversole	c36d963640	Update README to reflect completion of experiment	2025-05-29 13:39:44 -05:00
James Eversole	3717942589	Clean up and list SKI conversion fix	2025-04-24 12:14:38 -05:00
James Eversole	b8e2743103	Updates to demos	2025-04-16 14:23:53 -05:00
James Eversole	25bfe139e8	String escaping using backslash	2025-04-15 10:52:53 -05:00
James Eversole	f2beb86d8a	Drop backslash from lambda definitions	2025-04-15 10:34:38 -05:00
James Eversole	5024a2be4c	Revert flake.nix	2025-02-08 10:24:14 -06:00
James Eversole	fccee3e61c	Static linking part 2 Some checks failed Test, Build, and Release / test (push) Failing after 3h6m55s Details Test, Build, and Release / build (push) Has been cancelled Details	2025-02-07 19:22:31 -06:00
James Eversole	ad1918aa6f	Statically link binaries Some checks failed Test, Build, and Release / test (push) Failing after 50s Details Test, Build, and Release / build (push) Has been skipped Details	2025-02-07 18:32:09 -06:00
James Eversole	0a505172b4	Adds several new REPL utilities Also removes some broken list library functions	2025-02-07 18:25:11 -06:00
James Eversole	e6e18239a7	Smarter decoding of terms This update includes an update to `decodeResult` that makes string decoding far less aggressive. This also replaces the `!decode` REPL command with `!output` to allow users to switch output format on the fly. New tests are included for verifying decoding behavior; this group needs to be fleshed out further.	2025-02-07 15:06:25 -06:00
James Eversole	871245b567	Lint cleanup and README updates	2025-02-07 12:37:27 -06:00
James Eversole	30b9505d5f	Clearer definition for apply	2025-02-06 08:32:17 -06:00
James Eversole	f4e50353ed	Support for list literals in Lambdas All checks were successful Test, Build, and Release / test (push) Successful in 1m35s Details Test, Build, and Release / build (push) Successful in 1m12s Details	2025-02-02 12:08:08 -06:00
James Eversole	f9864b8361	REPL namespaces; lib function for pattern matching All checks were successful Test, Build, and Release / test (push) Successful in 1m52s Details Test, Build, and Release / build (push) Successful in 1m20s Details Adds support for REPL namespacing, primarily to avoid `main` collisions. Also adds a library function for an ergonomic pattern matching function that I've been noodling on. I might explore ways to make list syntax less annoying specifically for pattern matching like this.	2025-02-02 10:56:40 -06:00