Allow lambda expressions without explicit paren

Adds support for several special characters in identifiers. Adds a demo
for converting values to source code and another for checking equality.
Updates the existing demo and tests to reflect new names for functions
returning booleans.

.gitea/workflows/test-and-build.yml

@@ -0,0 +1,69 @@
+name: Test, Build, and Release
+
+on: 
+  push:
+    tags:
+      - '*'
+
+jobs:
+  test:
+    container:
+      image: docker.matri.cx/nix-runner:v0.1.0
+      credentials:
+        username: ${{ secrets.REGISTRY_USERNAME }}
+        password: ${{ secrets.REGISTRY_PASSWORD }}
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Set up cache for Cabal
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/cabal
+            ~/.config/cabal
+            ~/.local/state/cabal
+          key: cabal-${{ hashFiles('tricu.cabal') }}
+          restore-keys: |
+            cabal-
+
+      - name: Initialize Cabal and update package list
+        run: |
+          nix develop --command cabal update
+
+      - name: Run test suite
+        run: |
+          nix develop --command cabal test
+
+  build:
+    needs: test
+    container:
+      image: docker.matri.cx/nix-runner:v0.1.0
+      credentials:
+        username: ${{ secrets.REGISTRY_USERNAME }}
+        password: ${{ secrets.REGISTRY_PASSWORD }}
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Build and shrink binary
+        run: |
+          nix build
+          cp -L ./result/bin/tricu ./tricu
+          chmod 755 ./tricu
+          nix develop --command upx ./tricu
+  
+      - name: Setup go for release action
+        uses: actions/setup-go@v5
+        with:
+          go-version: '>=1.20.1'
+  
+      - name: Release binary
+        uses: https://gitea.com/actions/release-action@main
+        with:
+          files: |-
+            ./tricu
+          api_key: '${{ secrets.RELEASE_TOKEN }}'
+          pre_release: true

README.md

@@ -2,21 +2,22 @@
 
 ## Introduction
 
-tricu (pronounced like "tree-shoe" in English) is a purely functional interpreted language implemented in Haskell. [I'm](https://eversole.co) developing tricu to further research the possibilities offered by the various forms of [Tree Calculi](https://github.com/barry-jay-personal/typed_tree_calculus/blob/main/typed_program_analysis.pdf).
+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 is under active development and you can expect breaking changes with nearly every commit.
 
-tricu offers minimal syntax sugar yet manages to provide a complete, intuitive, and familiar programming environment. There is great power in simplicity. tricu offers:
+tricu is the word for "tree" in Lojban: `(x1) is a tree of species/cultivar (x2)`.
 
-1. `t` operator behaving by the rules of Tree Calculus
-1. Function definitions/assignments
-1. Lambda abstractions eliminated to Tree Calculus forms
-1. List, Number, and String literals
-1. Parentheses for grouping function application
+## Features
 
-These features move us cleanly out of the [turing tarpit](https://en.wikipedia.org/wiki/Turing_tarpit) territory that you may find yourself in if you try working only with the `t` operator.
+- Tree Calculus operator: `t`
+- Assignments: `x = t t`
+- 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 : lconcat a "!") [("Hello")]`
+- Intensionality blurs the distinction between functions and data (see REPL examples)
+- Immutability
 
-tricu is the word for "tree" in Lojban: `(x1) is a tree of species/cultivar (x2)`. This project was named "sapling" until I discovered the name is already being used for other (completely unrelated) programming language development projects.
-
-## What does it look like?
+## REPL examples
 
 ```
 tricu < -- Anything after `--` on a single line is a comment
@@ -26,19 +27,24 @@ tricu > "Hello,  world!"
 tricu < id (head (map (\i : lconcat i " world!") [("Hello, ")]))
 tricu > "Hello,  world!"
 
-tricu < -- Intensionality! We can inspect the structure of a function.
+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 < test t t
+tricu < test (t t)
 tricu > "Stem"
-tricu < -- We can even write a function to convert a function to source code
-tricu < toTString id
-tricu > "t (t (t t)) t"
+tricu < -- We can even convert a term back to source code (/demos/toSource.tri)
+tricu < toSource not?
+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
 ```
 
 ## Installation and Use
 
-You can easily build and/or run this project using [Nix](https://nixos.org/download/).
+[Releases are available for Linux.](https://git.eversole.co/James/tricu/releases)
+
+Or you can easily build and/or run this project using [Nix](https://nixos.org/download/).
 
 - Quick Start (REPL): 
   - `nix run git+https://git.eversole.co/James/tricu`
@@ -79,4 +85,4 @@ tricu decode [OPTIONS]
 
 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 playground created by [Johannes Bader](https://johannes-bader.com/) that introduced me to Tree Calculus. If tricu sounds interesting but compiling this repo sounds like a hassle, you should check out his site.
+[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.

demos/LevelOrderTraversal.tri

@@ -1,34 +0,0 @@
--- Level Order Traversal of a labelled binary tree
--- Objective: Print each "level" of the tree on a separate line
---
--- NOTICE: This demo relies on tricu base library functions
--- 
--- We model labelled binary trees as sublists where values act as labels. We
--- require explicit notation of empty nodes. Empty nodes can be represented 
--- with an empty list, `[]`, which is equivalent to a single node `t`. 
---
--- Example tree inputs:
--- [("1") [("2") [("4") t t] t] [("3") [("5") t t] [("6") t t]]]]
--- Graph:
---       1
---      / \
---     2   3
---    /   /  \
---   4   5    6
---
-
-isLeaf = (\node : lOr (emptyList node) (emptyList (tail node)))
-getLabel = (\node : head node)
-getLeft = (\node : if (emptyList node) [] (if (emptyList (tail node)) [] (head (tail node))))
-getRight = (\node : if (emptyList node) [] (if (emptyList (tail node)) [] (if (emptyList (tail (tail node))) [] (head (tail (tail node))))))
-
-processLevel = y (\self queue : if (emptyList queue) [] (pair (map getLabel queue) (self (filter (\node : not (emptyList node)) (lconcat (map getLeft queue) (map getRight queue))))))
-levelOrderTraversal = (\a : processLevel (t a t))
-toLineString = y (\self levels : if (emptyList levels) "" (lconcat (lconcat (map (\x : lconcat x " ") (head levels)) "") (if (emptyList (tail levels)) "" (lconcat (t (t 10 t) t) (self (tail levels))))))
-levelOrderToString = (\s : toLineString (levelOrderTraversal s))
-
-flatten = foldl (\acc x : lconcat acc x) ""
-flatLOT = (\s : lconcat (t 10 t) (flatten (levelOrderToString s)))
-
-exampleOne = flatLOT [("1") [("2") [("4") t t] t] [("3") [("5") t t] [("6") t t]]]]
-exampleTwo = flatLOT [("1") [("2") [("4") [("8") t t] [("9") t t]] [("6") [("10") t t] [("12") t t]]] [("3") [("5") [("11") t t] t] [("7") t t]]]

demos/equality.tri

@@ -0,0 +1,35 @@
+-- We represent `false` with a Leaf and `true` with a Stem Leaf
+demo_false = t
+demo_true  = t t
+
+-- Tree Calculus representation of the Boolean `not` function
+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)
+)
+-- 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
+-- 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.
+
+-- Let's see if these are the same:
+lambdaEqualsTC = equal? not_TC? not_Lambda?
+
+-- Here are some checks to verify their extensional behavior is the same:
+true_TC?  = not_TC? demo_false
+false_TC? = not_TC? demo_true
+
+true_Lambda?  = not_Lambda? demo_false
+false_Lambda? = not_Lambda? demo_true
+
+bothTrueEqual?  = equal? true_TC?  true_Lambda?
+bothFalseEqual? = equal? false_TC? false_Lambda?

demos/levelOrderTraversal.tri

@@ -0,0 +1,65 @@
+-- Level Order Traversal of a labelled binary tree
+-- Objective: Print each "level" of the tree on a separate line
+--
+-- NOTICE: This demo relies on tricu base library functions
+-- 
+-- We model labelled binary trees as sublists where values act as labels. We
+-- require explicit not?ation of empty nodes. Empty nodes can be represented 
+-- with an empty list, `[]`, which is equivalent to a single node `t`. 
+--
+-- Example tree inputs:
+-- [("1") [("2") [("4") t t] t] [("3") [("5") t t] [("6") t t]]]]
+-- Graph:
+--       1
+--      / \
+--     2   3
+--    /   /  \
+--   4   5    6
+--
+
+label = \node : head node
+
+left = (\node : if (emptyList? node)
+  [] 
+  (if (emptyList? (tail node)) 
+    [] 
+    (head (tail node))))
+
+right = (\node : if (emptyList? node) 
+  [] 
+  (if (emptyList? (tail node)) 
+    [] 
+    (if (emptyList? (tail (tail node))) 
+      [] 
+      (head (tail (tail node))))))
+
+processLevel = y (\self queue : if (emptyList? queue) 
+  [] 
+  (pair (map label queue) (self (filter 
+    (\node : not? (emptyList? node)) 
+      (lconcat (map left queue) (map right queue))))))
+
+levelOrderTraversal_ = \a : processLevel (t a t)
+
+toLineString = y (\self levels : if (emptyList? levels) 
+  "" 
+  (lconcat 
+    (lconcat (map (\x : lconcat x " ") (head levels)) "") 
+    (if (emptyList? (tail levels)) "" (lconcat (t (t 10 t) t) (self (tail levels))))))
+
+levelOrderToString = \s : toLineString (levelOrderTraversal_ s)
+
+flatten = foldl (\acc x : lconcat acc x) ""
+
+levelOrderTraversal = \s : lconcat (t 10 t) (flatten (levelOrderToString s))
+
+exampleOne = levelOrderTraversal [("1") 
+                                 [("2") [("4") t t] t] 
+                                 [("3") [("5") t t] [("6") t t]]]
+
+exampleTwo = levelOrderTraversal [("1") 
+                                 [("2") [("4") [("8") t t] [("9") t t]] 
+                                        [("6") [("10") t t] [("12") t t]]] 
+                                 [("3") [("5") [("11") t t] t] [("7") t t]]]
+
+exampleTwo

demos/size.tri

@@ -0,0 +1,21 @@
+compose = \f g x : f (g x)
+
+succ = y (\self : 
+  triage 
+    1 
+    t 
+    (triage 
+      (t (t t)) 
+      (\_ tail : t t (self tail)) 
+      t))
+
+size = (\x : 
+  (y (\self x : 
+    compose succ 
+      (triage 
+        (\x : x) 
+        self 
+        (\x y : compose (self x) (self y)) 
+        x)) x 0))
+
+size size

demos/toSource.tri

@@ -0,0 +1,46 @@
+-- Thanks to intensionality, we can inspect the structure of a given value
+-- even if it's a function. This includes lambdas which are eliminated to
+-- Tree Calculus (TC) terms during evaluation.
+
+-- `triage` takes four arguments: the first three represent behaviors for each 
+-- structural case in Tree Calculus (Leaf, Stem, and Fork).
+-- The fourth argument is the value whose structure is inspected. By evaluating 
+-- the Tree Calculus term, `triage` enables branching logic based on the term's 
+-- shape, making it possible to perform structure-specific operations such as
+-- reconstructing the terms' source code representation.
+-- triage = (\leaf stem fork : t (t leaf stem) fork)
+
+-- Base case of a single Leaf
+sourceLeaf = t (head "t")
+
+-- Stem case
+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.
+
+-- Fork case
+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.
+
+-- Wrapper around triage 
+toSource_ = y (\self arg :
+  triage
+    sourceLeaf        -- `triage` "a" case, Leaf
+    (sourceStem self) -- `triage` "b" case, Stem
+    (sourceFork self) -- `triage` "c" case, Fork
+    arg)              -- The term to be inspected
+
+-- toSource takes a single TC term and returns a String
+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)))"

flake.nix

@@ -32,10 +32,11 @@
         defaultPackage = self.packages.${system}.default;
 
         devShells.default = pkgs.mkShell {
-          buildInputs = with pkgs.haskellPackages; [
-            cabal-install
-            ghcid
+          buildInputs = with pkgs; [
+            haskellPackages.cabal-install
+            haskellPackages.ghcid
             customGHC
+            upx
           ];
           inputsFrom = builtins.attrValues self.packages.${system};
         };

lib/base.tri

@@ -1,41 +1,83 @@
 false = t
-_ = t
-true = t t
-k = t t
-i = t (t k) t
-s = t (t (k t)) t
-m = s i i
-b = s (k s) k
-c = s (s (k s) (s (k k) s)) (k k)
-iC = (\a b c : s a (k c) b)
-iD = b (b iC) iC
-iE = b (b iD) iC
-yi = (\i : b m (c b (i m)))
-y = yi iC
-yC = yi iD
-yD = yi iE
-id = (\a : a)
-triage = (\a b c : t (t a b) c)
-pair = t
-matchBool = (\ot of : triage of (\_ : ot) (\_ _ : ot))
-matchList = (\oe oc : triage oe _ oc)
-matchPair = (\op : triage _ _ op)
-not = matchBool false true
-and = matchBool id (\z : false)
-if = (\cond then else : t (t else (t t then)) t cond)
-test = triage "Leaf" (\z : "Stem") (\a b : "Fork")
-emptyList = matchList true (\y z : false)
-head = matchList t (\hd tl : hd)
-tail = matchList t (\hd tl : tl)
-lconcat = y (\self : matchList (\k : k) (\h r k : pair h (self r k)))
-lAnd = triage (\x : false) (\_ x : x) (\_ _ x : x)
-lOr = triage (\x : x) (\_ _ : true) (\_ _ x : true)
-hmap = y (\self : matchList (\f : t) (\hd tl f : pair (f hd) (self tl f)))
-map = (\f l : hmap l f)
-equal = y (\self : triage (triage true (\z : false) (\y z : false)) (\ax : triage false (self ax) (\y z : false)) (\ax ay : triage false (\z : false) (\bx by : lAnd (self ax bx) (self ay by))))
-hfilter = y (\self : matchList (\f : t) (\hd tl f : matchBool (t hd) i (f hd) (self tl f)))
-filter = (\f l : hfilter l f)
-hfoldl = y (\self f l x : matchList (\acc : acc) (\hd tl acc : self f tl (f acc hd)) l x)
-foldl  = (\f x l : hfoldl f l x)
-hfoldr = y (\self x f l : matchList x (\hd tl : f (self x f tl) hd) l)
-foldr  = (\f x l : hfoldr x f l)
+_     = t
+true  = t t
+k     = t t
+i     = t (t k) t
+s     = t (t (k t)) t
+m     = s i i
+b     = s (k s) k
+c     = s (s (k s) (s (k k) s)) (k k)
+id    = \a : a
+pair  = t
+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))
+
+triage = \leaf stem fork : t (t leaf stem) fork
+test   = triage "Leaf" (\_ : "Stem") (\_ _ : "Fork")
+
+matchBool = (\ot of : triage 
+  of 
+  (\_ : ot) 
+  (\_ _ : ot)
+)
+
+matchList = \a b : triage a _ b
+
+matchPair = \a   : triage _ _ a
+
+not? = matchBool false true
+and? = matchBool id (\_ : false)
+emptyList? = matchList true (\_ _ : false)
+
+head = matchList t (\head _ : head)
+tail = matchList t (\_ tail : tail)
+
+lconcat = y (\self : matchList 
+  (\k : k) 
+  (\h r k : pair h (self r k)))
+
+lAnd = (triage 
+  (\_     : false) 
+  (\_ x   : x) 
+  (\_ _ x : x))
+
+lOr = (triage 
+  (\x     : x) 
+  (\_ _   : true) 
+  (\_ _ _ : true))
+
+map_ = y (\self : 
+  matchList 
+    (\_ : t) 
+    (\head tail f : pair (f head) (self tail f)))
+map = \f l : map_ l f
+
+equal? = y (\self : triage 
+  (triage 
+    true 
+    (\_   : false) 
+    (\_ _ : false)) 
+  (\ax : 
+    triage 
+      false 
+      (self ax) 
+      (\_ _ : false)) 
+  (\ax ay : 
+    triage 
+      false 
+      (\_ : false) 
+      (\bx by : lAnd (self ax bx) (self ay by))))
+
+filter_ = y (\self : matchList 
+  (\_ : t) 
+  (\head tail f : matchBool (t head) i (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
+
+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

src/Eval.hs

@@ -8,110 +8,105 @@ import Data.Map  (Map)
 import qualified Data.Map as Map
 import qualified Data.Set as Set
 
-evalSingle :: Map String T -> TricuAST -> Map String T
-evalSingle env term = case term of
-  SFunc name [] body ->
-    let lineNoLambda = eliminateLambda body
-        result = evalAST env lineNoLambda
-    in Map.insert "__result" result (Map.insert name result env)
-  SLambda _ body ->
-    let result = evalAST env body
-    in Map.insert "__result" result env
-  SApp func arg ->
-    let result = apply (evalAST env $ eliminateLambda func) (evalAST env $ eliminateLambda arg)
-    in Map.insert "__result" result env
-  SVar name ->
-    case Map.lookup name env of
-      Just value -> Map.insert "__result" value env
-      Nothing -> errorWithoutStackTrace $ "Variable " ++ name ++ " not defined"
-  _ ->
-    let result = evalAST env term
-    in Map.insert "__result" result env
+evalSingle :: Env -> TricuAST -> Env
+evalSingle env term
+  | SFunc name [] body <- term =
+      if
+        | Map.member name env -> 
+            errorWithoutStackTrace $ 
+              "Error: Identifier '" ++ name ++ "' is already defined."
+        | otherwise -> 
+            let res = evalAST env body
+            in Map.insert "__result" res (Map.insert name res env)
+  | SApp func arg <- term =
+      let res = apply (evalAST env func) (evalAST env arg)
+      in Map.insert "__result" res env
+  | SVar name <- term =
+      case Map.lookup name env of
+        Just v  -> Map.insert "__result" v env
+        Nothing -> errorWithoutStackTrace $ "Variable `" ++ name ++ "` not defined"
+  | otherwise =
+      Map.insert "__result" (evalAST env term) env
 
-evalTricu :: Map String T -> [TricuAST] -> Map String T
-evalTricu env list = evalTricu' env (filter (/= SEmpty) list)
+evalTricu :: Env -> [TricuAST] -> Env
+evalTricu env []     = env
+evalTricu env [x]    =
+  let updatedEnv = evalSingle env x
+  in Map.insert "__result" (result updatedEnv) updatedEnv
+evalTricu env (x:xs) =
+  evalTricu (evalSingle env x) xs
+
+evalAST :: Env -> TricuAST -> T
+evalAST env term
+  | SLambda _ _ <- term = evalAST env (elimLambda term)
+  | SVar   name <- term = evalVar name
+  | TLeaf       <- term = Leaf
+  | TStem  t    <- term = Stem (evalAST env t)
+  | TFork  t u  <- term = Fork (evalAST env t) (evalAST env u)
+  | SApp   t u  <- term = apply (evalAST env t) (evalAST env u)
+  | SStr   s    <- term = ofString s
+  | SInt   n    <- term = ofNumber n
+  | SList  xs   <- term = ofList (map (evalAST env) xs)
+  | SEmpty      <- term = Leaf
+  | otherwise           = errorWithoutStackTrace "Unexpected AST term"
+    where
+      evalVar name = Map.findWithDefault
+        (errorWithoutStackTrace $ "Variable " ++ name ++ " not defined")
+        name env
+
+elimLambda :: TricuAST -> TricuAST
+elimLambda = go
   where
-  evalTricu' :: Map String T -> [TricuAST] -> Map String T
-  evalTricu' env [] = env
-  evalTricu' env [lastLine] =
-    let lastLineNoLambda = eliminateLambda lastLine
-        updatedEnv = evalSingle env lastLineNoLambda
-    in Map.insert "__result" (result updatedEnv) updatedEnv
-  evalTricu' env (line:rest) =
-    let lineNoLambda = eliminateLambda line
-        updatedEnv = evalSingle env lineNoLambda
-    in evalTricu updatedEnv rest
+    -- 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
+      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 == composeBody        = _COMPOSE
+      where
+        composeBody = SApp (SVar f) (SApp (SVar g) (SVar x))
+    -- 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
 
-evalAST :: Map String T -> TricuAST -> T
-evalAST env term = case term of
-  SVar name -> case Map.lookup name env of
-    Just value -> value
-    Nothing -> errorWithoutStackTrace $ "Variable " ++ name ++ " not defined"
-  TLeaf -> Leaf
-  TStem t -> Stem (evalAST env t)
-  TFork t1 t2 -> Fork (evalAST env t1) (evalAST env t2)
-  SApp t1 t2 -> apply (evalAST env t1) (evalAST env t2)
-  SStr str -> ofString str
-  SInt num -> ofNumber num
-  SList elems -> ofList (map (evalAST env) elems)
-  SEmpty -> Leaf
-  SFunc name args body ->
-    errorWithoutStackTrace $ "Unexpected function definition " ++ name
-  SLambda {} -> errorWithoutStackTrace "Internal error: SLambda found in evalAST after elimination."
+    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"
 
-eliminateLambda :: TricuAST -> TricuAST
-eliminateLambda (SLambda (v:vs) body)
-  | null vs = lambdaToT v (eliminateLambda body)
-  | otherwise = eliminateLambda (SLambda [v] (SLambda vs body))
-eliminateLambda (SApp f arg) = SApp (eliminateLambda f) (eliminateLambda arg)
-eliminateLambda (TStem t) = TStem (eliminateLambda t)
-eliminateLambda (TFork l r) = TFork (eliminateLambda l) (eliminateLambda r)
-eliminateLambda (SList xs) = SList (map eliminateLambda xs)
-eliminateLambda other = other
+    _S       = parseSingle "t (t (t t t)) t"
+    _K       = parseSingle "t t"
+    _I       = parseSingle "t (t (t t)) t"
+    _TRIAGE  = parseSingle "t (t (t t (t (t (t t t))))) t"
+    _COMPOSE = parseSingle "t (t (t t (t (t (t t t)) t))) (t t)"
+    
+    isFree x = Set.member x . freeVars
+    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 (SFunc   _ _ 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
 
--- https://github.com/barry-jay-personal/typed_tree_calculus/blob/main/typed_program_analysis.pdf
--- Chapter 4: Lambda-Abstraction
-lambdaToT :: String -> TricuAST -> TricuAST
-lambdaToT x (SVar y)
-  | x == y = tI
-lambdaToT x (SVar y)
-  | x /= y = SApp tK (SVar y)
-lambdaToT x t
-  | not (isFree x t) = SApp tK t
-lambdaToT x (SApp n u)
-  | not (isFree x (SApp n u)) = SApp tK (SApp (eliminateLambda n) (eliminateLambda u))
-lambdaToT x (SApp n u) = SApp (SApp tS (lambdaToT x (eliminateLambda n))) (lambdaToT x (eliminateLambda u))
-lambdaToT x body
-  | not (isFree x body) = SApp tK body
-  | otherwise = SApp (SApp tS (lambdaToT x body)) TLeaf
-
-freeVars :: TricuAST -> Set.Set String
-freeVars (SVar v) = Set.singleton v
-freeVars (SInt _) = Set.empty
-freeVars (SStr _) = Set.empty
-freeVars (SList xs) = foldMap freeVars xs
-freeVars (SApp f arg) = freeVars f <> freeVars arg
-freeVars TLeaf = Set.empty
-freeVars (SFunc _ _ b) = freeVars b
-freeVars (TStem t) = freeVars t
-freeVars (TFork l r) = freeVars l <> freeVars r
-freeVars (SLambda vs b) = foldr Set.delete (freeVars b) vs
-
-isFree :: String -> TricuAST -> Bool
-isFree x = Set.member x . freeVars
-
--- We need the SKI operators in an unevaluated TricuAST tree form so that we
--- can keep the evaluation functions straightforward
-tI :: TricuAST
-tI = SApp (SApp TLeaf (SApp TLeaf (SApp TLeaf TLeaf))) TLeaf
-
-tK :: TricuAST
-tK = SApp TLeaf TLeaf
-
-tS :: TricuAST
-tS = SApp (SApp TLeaf (SApp TLeaf (SApp (SApp TLeaf TLeaf) TLeaf))) TLeaf
-
-result :: Map String T -> T
+result :: Env -> T
 result r = case Map.lookup "__result" r of
   Just a -> a
   Nothing -> errorWithoutStackTrace "No __result field found in provided environment"

src/Lexer.hs

@@ -18,7 +18,10 @@ keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT
 identifier :: Lexer LToken
 identifier = do
   first <- letterChar <|> char '_'
-  rest <- many (letterChar <|> char '_' <|> char '-' <|> digitChar)
+  rest  <- many $ letterChar 
+              <|> digitChar 
+              <|> char '_' <|> char '-' <|> char '?' <|> char '!'
+              <|> char '$' <|> char '#' <|> char '@' <|> char '%'
   let name = first : rest
   if (name == "t" || name == "__result")
     then fail "Keywords (`t`, `__result`) cannot be used as an identifier"
@@ -61,7 +64,10 @@ lnewline :: Lexer LToken
 lnewline = char '\n' *> pure LNewline
 
 sc :: Lexer ()
-sc = space space1 (skipLineComment "--") (skipBlockComment "|-" "-|")
+sc = space
+  (void $ takeWhile1P (Just "space") (\c -> c == ' ' || c == '\t'))
+  (skipLineComment "--")
+  (skipBlockComment "|-" "-|")
 
 tricuLexer :: Lexer [LToken]
 tricuLexer = do
@@ -75,7 +81,8 @@ tricuLexer = do
   pure tokens
     where
       tricuLexer' = 
-        [ try identifier
+        [ try lnewline
+        , try identifier
         , try keywordT
         , try integerLiteral
         , try stringLiteral

src/Main.hs

@@ -81,4 +81,7 @@ main = do
       putStrLn $ decodeResult $ result $ evalTricu library $ parseTricu value
 
 runTricu :: String -> T
-runTricu = result . evalTricu Map.empty . parseTricu
+runTricu input =
+  let asts     = parseTricu input
+      finalEnv = evalTricu Map.empty asts
+   in result finalEnv

src/Parser.hs

@@ -1,277 +1,292 @@
 module Parser where
 
 import Lexer
-import Research hiding       (toList)
+import Research
 
-import Data.List.NonEmpty    (toList)
+import Control.Monad (void)
+import Control.Monad.State
+import Data.List.NonEmpty (toList)
 import Data.Void (Void)
 import Text.Megaparsec
-import Text.Megaparsec.Char
 import Text.Megaparsec.Error (ParseErrorBundle, errorBundlePretty)
-
 import qualified Data.Set as Set
 
-type Parser    = Parsec Void [LToken]
-type AltParser = Parsec Void String
+data PState = PState
+  { parenDepth  :: Int
+  , bracketDepth :: Int
+  } deriving (Show)
+
+type ParserM = StateT PState (Parsec Void [LToken])
+
+satisfyM :: (LToken -> Bool) -> ParserM LToken
+satisfyM f = do
+  token <- lift (satisfy f)
+  modify' (updateDepth token)
+  return token
+
+updateDepth :: LToken -> PState -> PState
+updateDepth LOpenParen    st = st { parenDepth   = parenDepth st   + 1 }
+updateDepth LOpenBracket  st = st { bracketDepth = bracketDepth st + 1 }
+updateDepth LCloseParen   st = st { parenDepth   = parenDepth st   - 1 }
+updateDepth LCloseBracket st = st { bracketDepth = bracketDepth st - 1 }
+updateDepth _ st = st
+
+topLevelNewline :: ParserM ()
+topLevelNewline = do
+  st <- get
+  if parenDepth st == 0 && bracketDepth st == 0
+    then void (satisfyM (== LNewline))
+    else fail "Top-level exit in nested context (paren or bracket)"
+
+parseProgram :: [LToken] -> Either (ParseErrorBundle [LToken] Void) [TricuAST]
+parseProgram tokens =
+  runParser (evalStateT (parseProgramM <* finalizeDepth <* eof) (PState 0 0)) "" tokens
+
+parseSingleExpr :: [LToken] -> Either (ParseErrorBundle [LToken] Void) TricuAST
+parseSingleExpr tokens =
+  runParser (evalStateT (scnParserM *> parseExpressionM <* finalizeDepth <* eof) (PState 0 0)) "" tokens
+
+finalizeDepth :: ParserM ()
+finalizeDepth = do
+  st <- get
+  case (parenDepth st, bracketDepth st) of
+    (0, 0) -> pure ()
+    (p, b) -> fail $ "Unmatched tokens: " ++ show (p, b)
 
 parseTricu :: String -> [TricuAST]
-parseTricu input
-  | null tokens = []
-  | otherwise = map parseSingle tokens
-  where
-    tokens = case lexTricu input of
-      [] -> []
-      tokens -> lines input
+parseTricu input =
+  case lexTricu input of
+    [] -> []
+    toks ->
+      case parseProgram toks of
+        Left err   -> errorWithoutStackTrace (handleParseError err)
+        Right asts -> asts
 
 parseSingle :: String -> TricuAST
-parseSingle input = case lexTricu input of
-  [] -> SEmpty
-  tokens -> case runParser parseExpression "" tokens of
-    Left err -> error $ handleParseError err
-    Right ast -> ast
+parseSingle input =
+  case lexTricu input of
+    [] -> SEmpty
+    toks ->
+      case parseSingleExpr toks of
+        Left err -> errorWithoutStackTrace (handleParseError err)
+        Right ast -> ast
 
-parseExpression :: Parser TricuAST
-parseExpression = choice
-  [ try parseFunction
-  , try parseLambda
-  , try parseLambdaExpression
-  , try parseListLiteral
-  , try parseApplication
-  , try parseTreeTerm
-  , parseLiteral
+parseProgramM :: ParserM [TricuAST]
+parseProgramM = do
+  skipMany topLevelNewline
+  exprs <- sepEndBy parseOneExpression (some topLevelNewline)
+  skipMany topLevelNewline
+  return exprs
+
+parseOneExpression :: ParserM TricuAST
+parseOneExpression = scnParserM *> parseExpressionM
+
+scnParserM :: ParserM ()
+scnParserM = skipMany $ do
+  t  <- lookAhead anySingle
+  st <- get
+  if | (parenDepth st > 0 || bracketDepth st > 0) && (t == LNewline) ->
+       void $ satisfyM (== LNewline)
+     | otherwise ->
+       fail "In nested context or no space token" <|> empty
+
+eofM :: ParserM ()
+eofM = lift eof
+
+parseExpressionM :: ParserM TricuAST
+parseExpressionM = choice
+  [ try parseFunctionM
+  , try parseLambdaM
+  , try parseLambdaExpressionM
+  , try parseListLiteralM
+  , try parseApplicationM
+  , try parseTreeTermM
+  , parseLiteralM
   ]
 
-scnParser :: Parser ()
-scnParser = skipMany (satisfy isNewline)
+parseFunctionM :: ParserM TricuAST
+parseFunctionM = do
+  let ident = (\case LIdentifier _ -> True; _ -> False)
+  LIdentifier name <- satisfyM ident
+  args <- many $ satisfyM ident
+  _    <- satisfyM (== LAssign)
+  scnParserM
+  body <- parseExpressionM
+  pure (SFunc name (map getIdentifier args) body)
 
-parseFunction :: Parser TricuAST
-parseFunction = do
-  LIdentifier name <- satisfy isIdentifier
-  args <- many (satisfy isIdentifier)
-  satisfy (== LAssign)
-  body <- parseExpression
-  return (SFunc name (map getIdentifier args) body)
+parseLambdaM :: ParserM TricuAST
+parseLambdaM = do
+  let ident = (\case LIdentifier _ -> True; _ -> False)
+  _      <- satisfyM (== LBackslash)
+  params <- some (satisfyM ident)
+  _      <- satisfyM (== LColon)
+  scnParserM
+  body  <- parseLambdaExpressionM
+  pure $ foldr (\param acc -> SLambda [getIdentifier param] acc) body params
 
-parseAtomicBase :: Parser TricuAST
-parseAtomicBase = choice
-    [ parseTreeLeaf
-    , parseGrouped
-    ]
-
-parseLambda :: Parser TricuAST
-parseLambda = between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) $ do
-  satisfy (== LBackslash)
-  param    <- satisfy isIdentifier
-  rest     <- many (satisfy isIdentifier)
-  satisfy (== LColon)
-  body     <- parseLambdaExpression
-  let nestedLambda = foldr (\v acc -> SLambda [v] acc) body (map getIdentifier rest)
-  return (SLambda [getIdentifier param] nestedLambda)
-
-parseLambdaExpression :: Parser TricuAST
-parseLambdaExpression = choice
-  [ try parseLambdaApplication
-  , parseAtomicLambda
+parseLambdaExpressionM :: ParserM TricuAST
+parseLambdaExpressionM = choice
+  [ try parseLambdaApplicationM
+  , parseAtomicLambdaM
   ]
 
-parseAtomicLambda :: Parser TricuAST
-parseAtomicLambda = choice
-  [ parseVar
-  , parseTreeLeaf
-  , parseLiteral
-  , parseListLiteral
-  , try parseLambda
-  , between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) parseLambdaExpression
+parseAtomicLambdaM :: ParserM TricuAST
+parseAtomicLambdaM = choice
+  [ parseVarM
+  , parseTreeLeafM
+  , parseLiteralM
+  , parseListLiteralM
+  , try parseLambdaM
+  , between (satisfyM (== LOpenParen)) (satisfyM (== LCloseParen)) parseLambdaExpressionM
   ]
 
-parseApplication :: Parser TricuAST
-parseApplication = do
-  func <- parseAtomicBase
-  args <- many parseAtomic
-  return $ foldl (\acc arg -> SApp acc arg) func args
+parseApplicationM :: ParserM TricuAST
+parseApplicationM = do
+  func <- parseAtomicBaseM
+  scnParserM
+  args <- many $ do
+    scnParserM
+    arg <- parseAtomicM
+    return arg
+  return $ foldl SApp func args
 
-parseLambdaApplication :: Parser TricuAST
-parseLambdaApplication = do
-  func <- parseAtomicLambda
-  args <- many parseAtomicLambda
-  return $ foldl (\acc arg -> SApp acc arg) func args
+parseLambdaApplicationM :: ParserM TricuAST
+parseLambdaApplicationM = do
+  func <- parseAtomicLambdaM
+  scnParserM
+  args <- many $ do
+    arg <- parseAtomicLambdaM
+    scnParserM
+    pure arg
+  pure $ foldl SApp func args
 
-isTreeTerm :: TricuAST -> Bool
-isTreeTerm TLeaf = True
-isTreeTerm (TStem _) = True
-isTreeTerm (TFork _ _) = True
-isTreeTerm _ = False
+parseAtomicBaseM :: ParserM TricuAST
+parseAtomicBaseM = choice
+  [ parseTreeLeafM
+  , parseGroupedM
+  ]
 
-parseTreeLeaf :: Parser TricuAST
-parseTreeLeaf = satisfy isKeywordT *> notFollowedBy (satisfy (== LAssign)) *> pure TLeaf
+parseTreeLeafM :: ParserM TricuAST
+parseTreeLeafM = do
+  let keyword = (\case LKeywordT -> True; _ -> False)
+  _ <- satisfyM keyword
+  notFollowedBy $ lift $ satisfy (== LAssign)
+  pure TLeaf
+
+parseTreeTermM :: ParserM TricuAST
+parseTreeTermM = do
+  base <- parseTreeLeafOrParenthesizedM
+  rest <- many parseTreeLeafOrParenthesizedM
+  pure (foldl combine base rest)
+  where
+    combine acc next
+      | TLeaf     <- acc = TStem next
+      | TStem t   <- acc = TFork t next
+      | TFork _ _ <- acc = TFork acc next
+
+parseTreeLeafOrParenthesizedM :: ParserM TricuAST
+parseTreeLeafOrParenthesizedM = choice
+  [ between (satisfyM (== LOpenParen)) (satisfyM (== LCloseParen)) parseTreeTermM
+  , parseTreeLeafM
+  ]
+
+parseAtomicM :: ParserM TricuAST
+parseAtomicM = choice
+  [ parseVarM
+  , parseTreeLeafM
+  , parseListLiteralM
+  , parseGroupedM
+  , parseLiteralM
+  ]
+
+parseGroupedM :: ParserM TricuAST
+parseGroupedM = between (satisfyM (== LOpenParen)) (satisfyM (== LCloseParen)) $
+  scnParserM *> parseExpressionM <* scnParserM
+
+parseLiteralM :: ParserM TricuAST
+parseLiteralM = choice
+  [ parseIntLiteralM
+  , parseStrLiteralM
+  ]
+
+parseListLiteralM :: ParserM TricuAST
+parseListLiteralM = do
+  _        <- satisfyM (== LOpenBracket)
+  elements <- many $ do
+    scnParserM
+    parseListItemM
+  scnParserM
+  _        <- satisfyM (== LCloseBracket)
+  pure (SList elements)
+
+parseListItemM :: ParserM TricuAST
+parseListItemM = choice
+  [ parseGroupedItemM
+  , parseListLiteralM
+  , parseSingleItemM
+  ]
+
+parseGroupedItemM :: ParserM TricuAST
+parseGroupedItemM = do
+  _     <- satisfyM (== LOpenParen)
+  inner <- parseExpressionM
+  _     <- satisfyM (== LCloseParen)
+  pure inner
+
+parseSingleItemM :: ParserM TricuAST
+parseSingleItemM = do
+  token <- satisfyM (\case LIdentifier _ -> True; LKeywordT -> True; _ -> False)
+  if | LIdentifier name <- token -> pure (SVar name)
+     | token == LKeywordT        -> pure TLeaf
+     | otherwise                 -> fail "Unexpected token in list item"
+
+parseVarM :: ParserM TricuAST
+parseVarM = do
+  satisfyM (\case LIdentifier _ -> True; _ -> False) >>= \case
+    LIdentifier name
+      | name == "t" || name == "__result" ->
+        fail ("Reserved keyword: " ++ name ++ " cannot be assigned.")
+      | otherwise                         ->
+         pure (SVar name)
+    _ -> fail "Unexpected token while parsing variable"
+
+parseIntLiteralM :: ParserM TricuAST
+parseIntLiteralM = do
+  let intL = (\case LIntegerLiteral _ -> True; _ -> False)
+  token <- satisfyM intL
+  if | LIntegerLiteral value <- token ->
+       pure (SInt value)
+     | otherwise                      ->
+       fail "Unexpected token while parsing integer literal"
+
+parseStrLiteralM :: ParserM TricuAST
+parseStrLiteralM = do
+  let strL = (\case LStringLiteral _ -> True; _ -> False)
+  token <- satisfyM strL
+  if | LStringLiteral value <- token ->
+       pure (SStr value)
+     | otherwise                     ->
+       fail "Unexpected token while parsing string literal"
 
 getIdentifier :: LToken -> String
 getIdentifier (LIdentifier name) = name
-getIdentifier _ = error "Expected identifier"
+getIdentifier _                  = errorWithoutStackTrace "Expected identifier"
 
-parseTreeTerm :: Parser TricuAST
-parseTreeTerm = do
-  base <- parseTreeLeafOrParenthesized
-  rest <- many parseTreeLeafOrParenthesized
-  pure $ foldl combine base rest
-  where
-    combine acc next = case acc of
-      TLeaf -> TStem next
-      TStem t -> TFork t next
-      TFork _ _ -> TFork acc next
-
-parseTreeLeafOrParenthesized :: Parser TricuAST
-parseTreeLeafOrParenthesized = choice
-  [ between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) parseTreeTerm
-  , parseTreeLeaf
-  ]
-
-foldTree :: [TricuAST] -> TricuAST
-foldTree [] = TLeaf
-foldTree [x] = x
-foldTree (x:y:rest) = TFork x (foldTree (y:rest))
-
-parseAtomic :: Parser TricuAST
-parseAtomic = choice
-  [ parseVar
-  , parseTreeLeaf
-  , parseListLiteral
-  , parseGrouped
-  , parseLiteral
-  ]
-
-parseGrouped :: Parser TricuAST
-parseGrouped = between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) parseExpression
-
-parseLiteral :: Parser TricuAST
-parseLiteral = choice
-  [ parseIntLiteral
-  , parseStrLiteral
-  ]
-
-parens :: Parser TricuAST -> Parser TricuAST
-parens p = do
-  satisfy (== LOpenParen)
-  result <- p
-  satisfy (== LCloseParen)
-  return result
-
-parseListLiteral :: Parser TricuAST
-parseListLiteral = do
-  satisfy (== LOpenBracket)
-  elements <- many parseListItem
-  satisfy (== LCloseBracket)
-  return (SList elements)
-
-parseListItem :: Parser TricuAST
-parseListItem = choice
-  [ parseGroupedItem
-  , parseListLiteral
-  , parseSingleItem
-  ]
-
-parseGroupedItem :: Parser TricuAST
-parseGroupedItem = do
-  satisfy (== LOpenParen)
-  inner <- parseExpression
-  satisfy (== LCloseParen)
-  return inner
-
-parseSingleItem :: Parser TricuAST
-parseSingleItem = do
-  token <- satisfy isListItem
-  case token of
-    LIdentifier name -> return (SVar name)
-    LKeywordT -> return TLeaf
-    _ -> fail "Unexpected token in list item"
-
-isListItem :: LToken -> Bool
-isListItem (LIdentifier _) = True
-isListItem LKeywordT = True
-isListItem _ = False
-
-parseVar :: Parser TricuAST
-parseVar = do
-  LIdentifier name <- satisfy isIdentifier
-  if (name == "t" || name == "__result")
-    then fail $ "Reserved keyword: " ++ name ++ " cannot be assigned."
-    else return (SVar name)
-
-parseIntLiteral :: Parser TricuAST
-parseIntLiteral = do
-  LIntegerLiteral value <- satisfy isIntegerLiteral
-  return (SInt value)
-
-parseStrLiteral :: Parser TricuAST
-parseStrLiteral = do
-  LStringLiteral value <- satisfy isStringLiteral
-  return (SStr value)
-
--- Boolean Helpers
-isKeywordT (LKeywordT) = True
-isKeywordT _ = False
-isIdentifier (LIdentifier _) = True
-isIdentifier _ = False
-isIntegerLiteral (LIntegerLiteral _) = True
-isIntegerLiteral _ = False
-isStringLiteral (LStringLiteral _) = True
-isStringLiteral _ = False
-isLiteral (LIntegerLiteral _) = True
-isLiteral (LStringLiteral _) = True
-isLiteral _ = False
-isNewline (LNewline) = True
-isNewline _ = False
-
--- Alternative parsers
-altSC :: AltParser ()
-altSC = skipMany (char ' ' <|> char '\t' <|> char '\n')
-
-parseTernaryTerm :: AltParser TricuAST
-parseTernaryTerm = do
-  altSC
-  term <- choice parseTernaryTerm'
-  altSC
-  pure term
-  where
-    parseTernaryTerm' =
-      [ try (between (char '(') (char ')') parseTernaryTerm)
-      , try parseTernaryLeaf
-      , try parseTernaryStem
-      , try parseTernaryFork
-      ]
-
-parseTernaryLeaf :: AltParser TricuAST
-parseTernaryLeaf = char '0' *> pure TLeaf
-
-parseTernaryStem :: AltParser TricuAST
-parseTernaryStem = char '1' *> (TStem <$> parseTernaryTerm)
-
-parseTernaryFork :: AltParser TricuAST
-parseTernaryFork = do
-  char '2'
-  term1 <- parseTernaryTerm
-  term2 <- parseTernaryTerm
-  pure $ TFork term1 term2
-
-parseTernary :: String -> Either String TricuAST
-parseTernary input = case runParser (parseTernaryTerm <* eof) "" input of
-  Left err -> Left (errorBundlePretty err)
-  Right ast -> Right ast
-
--- Error Handling
 handleParseError :: ParseErrorBundle [LToken] Void -> String
 handleParseError bundle =
   let errors = bundleErrors bundle
-      errorList = toList errors
-      formattedErrors = map showError errorList
+      formattedErrors = map formatError (Data.List.NonEmpty.toList errors)
   in unlines ("Parse error(s) encountered:" : formattedErrors)
 
-showError :: ParseError [LToken] Void -> String
-showError (TrivialError offset (Just (Tokens tokenStream)) expected) =
-  "Parse error at offset " ++ show offset ++ ": unexpected token "
-  ++ show tokenStream ++ ", expected one of " ++ show (Set.toList expected)
-showError (FancyError offset fancy) =
-  "Parse error at offset " ++ show offset ++ ":\n " ++ unlines (map show (Set.toList fancy))
-showError (TrivialError offset Nothing expected) =
-  "Parse error at offset " ++ show offset ++ ": expected one of "
-  ++ show (Set.toList expected)
+formatError :: ParseError [LToken] Void -> String
+formatError (TrivialError offset unexpected expected) =
+  let unexpectedMsg = case unexpected of
+        Just x  -> "unexpected token " ++ show x
+        Nothing -> "unexpected end of input"
+      expectedMsg = if null expected
+        then ""
+        else "expected " ++ show (Set.toList expected)
+  in "Parse error at offset " ++ show offset ++ ": " ++ unexpectedMsg ++
+     if null expectedMsg then "" else " " ++ expectedMsg
+formatError (FancyError offset _) =
+  "Parse error at offset " ++ show offset ++ ": unexpected FancyError"

src/REPL.hs

@@ -20,37 +20,36 @@ repl env = runInputT defaultSettings (loop env)
     loop :: Env -> InputT IO ()
     loop env = do
       minput <- getInputLine "tricu < "
-      case minput of
-        Nothing -> outputStrLn "Exiting tricu"
-        Just s -> case strip s of 
-          "!exit" -> outputStrLn "Exiting tricu"
-          "!load" -> do
-            path <- getInputLine "File path to load < "
-            case path of
-              Nothing -> do
-                outputStrLn "No input received; stopping import."
-                loop env
-              Just path -> do
-                loadedEnv <- liftIO $ evaluateFileWithContext env (strip path)
-                loop $ Map.delete "__result" (Map.union loadedEnv env)
-          "" -> do
-            outputStrLn ""
-            loop env
-          input -> do
-            case (take 2 input) of 
-              "--" -> loop env
-              _ -> do
-                newEnv <- liftIO $ (processInput env input `catch` errorHandler env)
-                loop newEnv
-  
+      if
+        | Nothing <- minput                     -> outputStrLn "Exiting tricu"
+        | Just s  <- minput, strip s == "!exit" -> outputStrLn "Exiting tricu"
+        | Just s  <- minput, strip s == ""      -> do
+          outputStrLn ""
+          loop env
+        | Just s  <- minput, strip s == "!load" -> do
+          path <- getInputLine "File path to load < "
+          if
+            | Nothing <- path -> do
+              outputStrLn "No input received; stopping import."
+              loop env
+            | Just p  <- path -> do
+              loadedEnv <- liftIO $ evaluateFileWithContext env (strip p) `catch` \e -> errorHandler env e
+              loop $ Map.delete "__result" (Map.union loadedEnv env)
+        | Just s <- minput -> do
+          if
+            | take 2 s == "--" -> loop env
+            | otherwise -> do
+              newEnv <- liftIO $ processInput env s `catch` errorHandler env
+              loop newEnv
+
     processInput :: Env -> String -> IO Env
     processInput env input = do
-      let asts = parseTricu input
+      let asts   = parseTricu input
           newEnv = evalTricu env asts
-      case Map.lookup "__result" newEnv of
-        Just r -> do
+      if
+        | Just r <- Map.lookup "__result" newEnv -> do
           putStrLn $ "tricu > " ++ decodeResult r
-        Nothing -> return ()
+        | otherwise -> return ()
       return newEnv
     
     errorHandler :: Env -> SomeException -> IO (Env)
@@ -62,10 +61,8 @@ repl env = runInputT defaultSettings (loop env)
     strip = dropWhileEnd isSpace . dropWhile isSpace
 
 decodeResult :: T -> String
-decodeResult tc = case toNumber tc of
-  Right num -> show num
-  Left _ -> case toString tc of
-    Right str -> "\"" ++ str ++ "\""
-    Left _ -> case toList tc of
-      Right list -> "[" ++ intercalate ", " (map decodeResult list) ++ "]"
-      Left _ -> formatResult TreeCalculus tc
+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

src/Research.hs

@@ -28,7 +28,7 @@ data TricuAST
   | SEmpty
   deriving (Show, Eq, Ord)
 
--- Tokens from Lexer
+-- Lexer Tokens
 data LToken
   = LKeywordT
   | LIdentifier String
@@ -61,19 +61,6 @@ 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
 
--- SKI Combinators
-_S :: T
-_S = Fork (Stem (Fork Leaf Leaf)) Leaf
-
-_K :: T
-_K = Stem Leaf
-
--- Identity
--- We use the "point-free" style which drops a redundant node
--- Full I form (SKK): Fork (Stem (Stem Leaf)) (Stem Leaf)
-_I :: T
-_I = Fork (Stem (Stem Leaf)) Leaf 
-
 -- Booleans
 _false :: T
 _false = Leaf

test/Spec.hs

@@ -25,185 +25,216 @@ runTricu s = show $ result (evalTricu Map.empty $ parseTricu s)
 
 tests :: TestTree
 tests = testGroup "Tricu Tests"
-  [ lexerTests
-  , parserTests
-  , evaluationTests
-  , lambdaEvalTests
-  , libraryTests
-  , fileEvaluationTests
-  , propertyTests
+  [ lexer
+  , parser
+  , simpleEvaluation
+  , lambdas
+  , baseLibrary
+  , fileEval
+  , demos
   ]
 
-lexerTests :: TestTree
-lexerTests = testGroup "Lexer Tests"
+lexer :: TestTree
+lexer = testGroup "Lexer Tests"
   [ testCase "Lex simple identifiers" $ do
       let input = "x a b = a"
           expect = Right [LIdentifier "x", LIdentifier "a", LIdentifier "b", LAssign, LIdentifier "a"]
       runParser tricuLexer "" input @?= expect
+
   , testCase "Lex Tree Calculus terms" $ do
       let input = "t t t"
           expect = Right [LKeywordT, LKeywordT, LKeywordT]
       runParser tricuLexer "" input @?= expect
+
   , testCase "Lex escaped characters in strings" $ do
       let input = "\"hello\\nworld\""
           expect = Right [LStringLiteral "hello\\nworld"]
       runParser tricuLexer "" input @?= expect
+
   , testCase "Lex mixed literals" $ do
       let input = "t \"string\" 42"
           expect = Right [LKeywordT, LStringLiteral "string", LIntegerLiteral 42]
       runParser tricuLexer "" input @?= expect
+
   , testCase "Lex invalid token" $ do
       let input = "&invalid"
       case runParser tricuLexer "" input of
         Left _ -> return ()
         Right _ -> assertFailure "Expected lexer to fail on invalid token"
+
   , testCase "Drop trailing whitespace in definitions" $ do
       let input = "x = 5 "
           expect = [LIdentifier "x",LAssign,LIntegerLiteral 5]
       case (runParser tricuLexer "" input) of
         Left _ -> assertFailure "Failed to lex input"
         Right i -> i @?= expect
+
   , testCase "Error when using invalid characters in identifiers" $ do
         case (runParser tricuLexer "" "__result = 5") of
           Left _ -> return ()
           Right _ -> assertFailure "Expected failure when trying to assign the value of __result"
   ]
 
-parserTests :: TestTree
-parserTests = testGroup "Parser Tests"
+parser :: TestTree
+parser = testGroup "Parser Tests"
   [ testCase "Error when assigning a value to T" $ do
-      let input = lexTricu "t = x"
-      case (runParser parseExpression "" input) of
-        Left _ -> return ()
+      let tokens = lexTricu "t = x" 
+      case parseSingleExpr tokens of
+        Left  _ -> return ()
         Right _ -> assertFailure "Expected failure when trying to assign the value of T"
+
   , testCase "Parse function definitions" $ do
       let input = "x = (\\a b c : a)"
           expect = SFunc "x" [] (SLambda ["a"] (SLambda ["b"] (SLambda ["c"] (SVar "a"))))
       parseSingle input @?= expect
+
   , testCase "Parse nested Tree Calculus terms" $ do
       let input = "t (t t) t"
           expect = SApp (SApp TLeaf (SApp TLeaf TLeaf)) TLeaf
       parseSingle input @?= expect
+
   , testCase "Parse sequential Tree Calculus terms" $ do
       let input = "t t t"
           expect = SApp (SApp TLeaf TLeaf) TLeaf
       parseSingle input @?= expect
+
   , testCase "Parse mixed list literals" $ do
       let input = "[t (\"hello\") t]"
           expect = SList [TLeaf, SStr "hello", TLeaf]
       parseSingle input @?= expect
+
   , testCase "Parse function with applications" $ do
       let input  = "f = (\\x : t x)"
           expect = SFunc "f" [] (SLambda ["x"] (SApp TLeaf (SVar "x")))
       parseSingle input @?= expect
+
   , testCase "Parse nested lists" $ do
       let input  = "[t [(t t)]]"
           expect = SList [TLeaf,SList [SApp TLeaf TLeaf]]
       parseSingle input @?= expect
+
   , testCase "Parse complex parentheses" $ do
       let input  = "t (t t (t t))"
           expect = SApp TLeaf (SApp (SApp TLeaf TLeaf) (SApp TLeaf TLeaf))
       parseSingle input @?= expect
+
   , testCase "Parse empty list" $ do
       let input  = "[]"
           expect = SList []
       parseSingle input @?= expect
+
   , testCase "Parse multiple nested lists" $ do
       let input  = "[[t t] [t (t t)]]"
           expect = SList [SList [TLeaf,TLeaf],SList [TLeaf,SApp TLeaf TLeaf]]
       parseSingle input @?= expect
+
   , testCase "Parse whitespace variance" $ do
       let input1 = "[t t]"
       let input2 = "[ t t ]"
           expect = SList [TLeaf, TLeaf]
       parseSingle input1 @?= expect
       parseSingle input2 @?= expect
+
   , testCase "Parse string in list" $ do
       let input  = "[(\"hello\")]"
           expect = SList [SStr "hello"]
       parseSingle input @?= expect
+
   , testCase "Parse parentheses inside list" $ do
       let input  = "[t (t t)]"
           expect = SList [TLeaf,SApp TLeaf TLeaf]
       parseSingle input @?= expect
+
   , testCase "Parse nested parentheses in function body" $ do
       let input  = "f = (\\x : t (t (t t)))"
           expect = SFunc "f" [] (SLambda ["x"] (SApp TLeaf (SApp TLeaf (SApp TLeaf TLeaf))))
       parseSingle input @?= expect
+
   , testCase "Parse lambda abstractions" $ do
       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)"
           expect = SFunc "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)"
           expect = [SFunc "x" [] (SLambda ["a"] (SVar "a")),SApp (SVar "x") TLeaf]
       parseTricu input @?= expect
+
   , testCase "Comments 1" $ do
       let input = "(t) (t) -- (t)"
           expect = [SApp TLeaf TLeaf]
       parseTricu input @?= expect
+
   , testCase "Comments 2" $ do
       let input = "(t) -- (t) -- (t)"
           expect = [TLeaf]
       parseTricu input @?= expect
-  , testCase "Comments with no terms" $ do
-      let input = unlines ["-- (t)", "(t t)"]
-          expect = [SEmpty,SApp TLeaf TLeaf]
-      parseTricu input @?= expect 
   ]
 
-evaluationTests :: TestTree
-evaluationTests = testGroup "Evaluation Tests"
+simpleEvaluation :: TestTree
+simpleEvaluation = testGroup "Evaluation Tests"
   [ testCase "Evaluate single Leaf" $ do
       let input = "t"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= Leaf
+
   , testCase "Evaluate single Stem" $ do
       let input = "t t"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= Stem Leaf
+
   , testCase "Evaluate single Fork" $ do
       let input = "t t t"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= Fork Leaf Leaf
+
   , testCase "Evaluate nested Fork and Stem" $ do
       let input = "t (t t) t"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= Fork (Stem Leaf) Leaf
+
   , testCase "Evaluate `not` function" $ do
       let input = "t (t (t t) (t t t)) t"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?=
         Fork (Fork (Stem Leaf) (Fork Leaf Leaf)) Leaf
+
   , testCase "Environment updates with definitions" $ do
       let input = "x = t\ny = x"
           env = evalTricu Map.empty (parseTricu input)
       Map.lookup "x" env @?= Just Leaf
       Map.lookup "y" env @?= Just Leaf
+
   , testCase "Variable substitution" $ do
       let input = "x = t t\ny = t x\ny"
           env = evalTricu Map.empty (parseTricu input)
       (result env) @?= Stem (Stem Leaf)
+
   , testCase "Multiline input evaluation" $ do
       let input = "x = t\ny = t t\nx"
           env = evalTricu Map.empty (parseTricu input)
       (result env) @?= Leaf
+
   , testCase "Evaluate string literal" $ do
       let input = "\"hello\""
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= ofString "hello"
+
   , testCase "Evaluate list literal" $ do
       let input = "[t (t t)]"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= ofList [Leaf, Stem Leaf]
+
   , testCase "Evaluate empty list" $ do
       let input = "[]"
       let ast = parseSingle input
       (result $ evalSingle Map.empty ast) @?= ofList []
+
   , testCase "Evaluate variable dependency chain" $ do
       let input = "x = t (t t)\n \
                   \ y = x\n \
@@ -212,10 +243,17 @@ evaluationTests = testGroup "Evaluation Tests"
                   \ variablewithamuchlongername"
           env = evalTricu Map.empty (parseTricu input)
       (result env) @?= (Stem (Stem Leaf))
-  , testCase "Evaluate variable shadowing" $ do
+
+
+  , testCase "Immutable definitions" $ do
       let input = "x = t t\nx = t\nx"
           env = evalTricu Map.empty (parseTricu input)
-      (result env) @?= Leaf
+      result <- try (evaluate (runTricu input)) :: IO (Either SomeException String)
+      case result of
+        Left  _ -> return ()
+        Right _ -> assertFailure "Expected evaluation error"
+
+
   , testCase "Apply identity to Boolean Not" $ do
       let not = "(t (t (t t) (t t t)) t)"
       let input = "x = (\\a : a)\nx " ++ not
@@ -223,204 +261,258 @@ evaluationTests = testGroup "Evaluation Tests"
       result env @?= Fork (Fork (Stem Leaf) (Fork Leaf Leaf)) Leaf
   ]
 
-lambdaEvalTests :: TestTree
-lambdaEvalTests = testGroup "Lambda Evaluation Tests"
+lambdas :: TestTree
+lambdas = testGroup "Lambda Evaluation Tests"
   [ testCase "Lambda Identity Function" $ do
       let input = "id = (\\x : x)\nid t"
       runTricu input @?= "Leaf"
+
   , testCase "Lambda Constant Function (K combinator)" $ do
       let input = "k = (\\x y : x)\nk t (t t)"
       runTricu input @?= "Leaf"
+
   , testCase "Lambda Application with Variable" $ do
       let input = "id = (\\x : x)\nval = t t\nid val"
       runTricu 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"
+
    , 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"
+
   , testCase "Lambda with a complex body" $ do
       let input = "f = (\\x : t (t x))\nf t"
       runTricu 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"
+
   , testCase "Lambda with Shadowing" $ do
       let input = "f = (\\x : (\\x : x))\nf t (t t)"
       runTricu 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"
+
    , testCase "Lambda with free variables" $ do
       let input = "y = t t\nf = (\\x : y)\nf t"
       runTricu 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)"
+
    , 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"
+
    , 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))"
+
     , 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)"
+
     , testCase "Lambda applying a variable" $ do
         let input = "id = (\\x : x)\na = t t\nid a"
         runTricu 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"
+
   , 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 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 with a list literal" $ do
         let input = "f = (\\x : x)\nf [t (t t)]"
         runTricu input @?= "Fork Leaf (Fork (Stem Leaf) Leaf)"
   ]
 
-libraryTests :: TestTree
-libraryTests = testGroup "Library Tests"
+baseLibrary :: TestTree
+baseLibrary = testGroup "Library Tests"
   [ testCase "K combinator 1" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "k (t) (t t)"
           env = evalTricu library (parseTricu input)
       result env @?= Leaf
+
   , testCase "K combinator 2" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "k (t t) (t)"
           env = evalTricu library (parseTricu input)
       result env @?= Stem Leaf
+
   , testCase "K combinator 3" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "k (t t t) (t)"
           env = evalTricu library (parseTricu input)
       result env @?= Fork Leaf Leaf
+
   , testCase "S combinator" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "s (t) (t) (t)"
           env = evalTricu library (parseTricu input)
       result env @?= Fork Leaf (Stem Leaf)
+
   , testCase "SKK == I (fully expanded)" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "s k k"
           env = evalTricu library (parseTricu input)
       result env @?= Fork (Stem (Stem Leaf)) (Stem Leaf)
+
   , testCase "I combinator" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "i not"
+      let input = "i not?"
           env = evalTricu library (parseTricu input)
       result env @?= Fork (Fork (Stem Leaf) (Fork Leaf Leaf)) (Fork Leaf (Fork Leaf Leaf))
+
   , testCase "Triage test Leaf" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "test t"
           env = decodeResult $ result $ evalTricu library (parseTricu input)
       env @?= "\"Leaf\""
+
   , testCase "Triage test (Stem Leaf)" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "test (t t)"
           env = decodeResult $ result $ evalTricu library (parseTricu input)
       env @?= "\"Stem\""
+
   , testCase "Triage test (Fork Leaf Leaf)" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "test (t t t)"
           env = decodeResult $ result $ evalTricu library (parseTricu input)
       env @?= "\"Fork\""
+
   , testCase "Boolean NOT: true" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "not true"
+      let input = "not? true"
           env = result $ evalTricu library (parseTricu input)
       env @?= Leaf
+
   , testCase "Boolean NOT: false" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "not false"
+      let input = "not? false"
           env = result $ evalTricu library (parseTricu input)
       env @?= Stem Leaf
+
+
   , testCase "Boolean AND TF" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "and (t t) (t)"
+      let input = "and? (t t) (t)"
           env = evalTricu library (parseTricu input)
       result env @?= Leaf
+
   , testCase "Boolean AND FT" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "and (t) (t t)"
+      let input = "and? (t) (t t)"
           env = evalTricu library (parseTricu input)
       result env @?= Leaf
+
   , testCase "Boolean AND FF" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "and (t) (t)"
+      let input = "and? (t) (t)"
           env = evalTricu library (parseTricu input)
       result env @?= Leaf
+
   , testCase "Boolean AND TT" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "and (t t) (t t)"
+      let input = "and? (t t) (t t)"
           env = evalTricu library (parseTricu input)
       result env @?= Stem Leaf
+
   , testCase "List head" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "head [(t) (t t) (t t t)]"
           env = evalTricu library (parseTricu input)
       result env @?= Leaf
+
   , testCase "List tail" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "head (tail (tail [(t) (t t) (t t t)]))"
           env = evalTricu library (parseTricu input)
       result env @?= Fork Leaf Leaf
+
   , testCase "List map" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "head (tail (map (\\a : (t t t)) [(t) (t) (t)]))"
           env = evalTricu library (parseTricu input)
       result env @?= Fork Leaf Leaf
+
   , testCase "Empty list check" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "emptyList []"
+      let input = "emptyList? []"
           env = evalTricu library (parseTricu input)
       result env @?= Stem Leaf
+
   , testCase "Non-empty list check" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "not (emptyList [(1) (2) (3)])"
+      let input = "not? (emptyList? [(1) (2) (3)])"
           env = evalTricu library (parseTricu input)
       result env @?= Stem Leaf
+
   , testCase "Concatenate strings" $ do
       library <- evaluateFile "./lib/base.tri"
       let input = "lconcat \"Hello, \" \"world!\""
           env = decodeResult $ result $ evalTricu library (parseTricu input)
       env @?= "\"Hello, world!\""
+
   , testCase "Verifying Equality" $ do
       library <- evaluateFile "./lib/base.tri"
-      let input = "equal (t t t) (t t t)"
+      let input = "equal? (t t t) (t t t)"
           env = evalTricu library (parseTricu input)
       result env @?= Stem Leaf
   ]
 
-fileEvaluationTests :: TestTree
-fileEvaluationTests = testGroup "Evaluation tests"
+fileEval :: TestTree
+fileEval = testGroup "File evaluation tests"
   [ testCase "Forks" $ do
       res <- liftIO $ evaluateFileResult "./test/fork.tri"
       res @?= Fork Leaf Leaf
+
   , testCase "File ends with comment" $ do
       res <- liftIO $ evaluateFileResult "./test/comments-1.tri"
       res @?= Fork (Stem Leaf) Leaf
+
   , testCase "Mapping and Equality" $ do
       res <- liftIO $ evaluateFileResult "./test/map.tri"
       res @?= Stem Leaf
+
   , testCase "Eval and decoding string" $ do
       library <- liftIO $ evaluateFile "./lib/base.tri"
       res <- liftIO $ evaluateFileWithContext library "./test/string.tri"
       decodeResult (result res) @?= "\"String test!\""
   ]
 
-propertyTests :: TestTree
-propertyTests = testGroup "Property Tests"
-  [ testProperty "Lexing and parsing round-trip" $ \input ->
-      case runParser tricuLexer "" input of
-        Left _ -> property True
-        Right tokens -> case runParser parseExpression "" tokens of
-          Left _ -> property True
-          Right ast -> parseSingle input === ast
+demos :: TestTree
+demos = testGroup "Test provided demo functionality"
+  [ testCase "Structural equality demo" $ do
+      library <- liftIO $ evaluateFile "./lib/base.tri"
+      res     <- liftIO $ evaluateFileWithContext library "./demos/equality.tri"
+      decodeResult (result res) @?= "t t"
+  , testCase "Convert values back to source code demo" $ do
+      library <- liftIO $ evaluateFile "./lib/base.tri"
+      res     <- liftIO $ evaluateFileWithContext library "./demos/toSource.tri"
+      decodeResult (result res) @?= "\"(t (t (t t) (t t t)) (t t (t t t)))\""
+  , testCase "Determining the size of functions" $ do
+      library <- liftIO $ evaluateFile "./lib/base.tri"
+      res     <- liftIO $ evaluateFileWithContext library "./demos/size.tri"
+      decodeResult (result res) @?= "454"
+  , testCase "Level Order Traversal demo" $ do
+      library <- liftIO $ evaluateFile "./lib/base.tri"
+      res     <- liftIO $ evaluateFileWithContext library "./demos/levelOrderTraversal.tri"
+      decodeResult (result res) @?= "\"\n1 \n2 3 \n4 5 6 7 \n8 11 10 9 12 \""
   ]

tricu.cabal

@@ -1,7 +1,7 @@
 cabal-version: 1.12
 
 name:           tricu
-version:        0.5.0
+version:        0.9.0
 description:    A micro-language for exploring Tree Calculus
 author:         James Eversole
 maintainer:     james@eversole.co
@@ -18,6 +18,8 @@ executable tricu
       src
   default-extensions:
       DeriveDataTypeable
+      LambdaCase
+      MultiWayIf
       OverloadedStrings
   ghc-options: -threaded -rtsopts -with-rtsopts=-N -optl-pthread -fPIC
   build-depends:
@@ -43,6 +45,8 @@ test-suite tricu-tests
   hs-source-dirs:      test, src
   default-extensions:
       DeriveDataTypeable
+      LambdaCase
+      MultiWayIf
       OverloadedStrings
   build-depends:       
     base