Somewhat working lambdas

Architectural changes to lambda evaluation and parsing to allow
for correct expression evaluation. Contains several failing AI-generated
tests and we're still failing tests for erroring incomplete definitions

src/Parser.hs

@@ -1,10 +1,8 @@
 module Parser where
 
 import Debug.Trace
-
 import Lexer
 import Research hiding (toList)
-
 import Control.Exception (throw)
 import Data.List.NonEmpty (toList)
 import qualified Data.Set as Set
@@ -14,17 +12,18 @@ import Text.Megaparsec.Char
 import Text.Megaparsec.Error (errorBundlePretty, ParseErrorBundle)
 
 type Parser = Parsec Void [LToken]
+
 data SaplingAST
-  = SVar    String
-  | SInt    Int
-  | SStr    String
-  | SList   [SaplingAST]
-  | SFunc   String       [String]     SaplingAST
-  | SApp    SaplingAST   SaplingAST
+  = SVar String
+  | SInt Int
+  | SStr String
+  | SList [SaplingAST]
+  | SFunc String [String] SaplingAST
+  | SApp SaplingAST SaplingAST
   | TLeaf
-  | TStem   SaplingAST
-  | TFork   SaplingAST   SaplingAST
-  | SLambda [String]     SaplingAST
+  | TStem SaplingAST
+  | TFork SaplingAST SaplingAST
+  | SLambda [String] SaplingAST
   deriving (Show, Eq, Ord)
 
 parseSapling :: String -> [SaplingAST]
@@ -35,7 +34,7 @@ parseSapling input =
 parseSingle :: String -> SaplingAST
 parseSingle "" = error "Empty input provided to parseSingle"
 parseSingle input = case runParser parseExpression "" (lexSapling input) of
-  Left  err -> error $ handleParseError err
+  Left err -> error $ handleParseError err
   Right ast -> ast
 
 scnParser :: Parser ()
@@ -45,6 +44,7 @@ parseExpression :: Parser SaplingAST
 parseExpression = choice
   [ try parseFunction
   , try parseLambda
+  , try parseLambdaExpression
   , try parseListLiteral
   , try parseApplication
   , try parseTreeTerm
@@ -59,6 +59,19 @@ parseFunction = do
   body <- parseExpression
   return (SFunc name (map getIdentifier args) body)
 
+parseAtomicBase :: Parser SaplingAST
+parseAtomicBase = choice
+    [ try parseVarWithoutAssignment
+    , parseTreeLeaf
+    , parseGrouped
+    ]
+parseVarWithoutAssignment :: Parser SaplingAST
+parseVarWithoutAssignment = do
+    LIdentifier name <- satisfy isIdentifier
+    if (name == "t" || name == "__result")
+    then fail $ "Reserved keyword: " ++ name ++ " cannot be assigned."
+    else notFollowedBy (satisfy (== LAssign)) *> return (SVar name)
+
 parseLambda :: Parser SaplingAST
 parseLambda = between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) $ do
   satisfy (== LBackslash)
@@ -81,6 +94,7 @@ parseAtomicLambda = choice
   , parseTreeLeaf
   , parseLiteral
   , parseListLiteral
+  , try parseLambda
   , between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) parseLambdaExpression
   ]
 
@@ -92,22 +106,15 @@ parseApplication = do
 
 parseLambdaApplication :: Parser SaplingAST
 parseLambdaApplication = do
-    func <- parseAtomicLambda
-    args <- many parseAtomicLambda
-    return $ foldl (\acc arg -> SApp acc arg) func args
+  func <- parseAtomicLambda
+  args <- many parseAtomicLambda
+  return $ foldl (\acc arg -> SApp acc arg) func args
 
 isTreeTerm :: SaplingAST -> Bool
-isTreeTerm TLeaf       = True
-isTreeTerm (TStem _)   = True
+isTreeTerm TLeaf = True
+isTreeTerm (TStem _) = True
 isTreeTerm (TFork _ _) = True
-isTreeTerm _           = False
-
-parseAtomicBase :: Parser SaplingAST
-parseAtomicBase = choice
-  [ parseVar
-  , parseTreeLeaf
-  , parseGrouped
-  ]
+isTreeTerm _ = False
 
 parseTreeLeaf :: Parser SaplingAST
 parseTreeLeaf = satisfy isKeywordT *> notFollowedBy (satisfy (== LAssign)) *> pure TLeaf
@@ -123,8 +130,8 @@ parseTreeTerm = do
   pure $ foldl combine base rest
   where
     combine acc next = case acc of
-      TLeaf     -> TStem next
-      TStem t   -> TFork t next
+      TLeaf -> TStem next
+      TStem t -> TFork t next
       TFork _ _ -> TFork acc next
 
 parseTreeLeafOrParenthesized :: Parser SaplingAST
@@ -147,7 +154,6 @@ parseAtomic = choice
   , parseLiteral
   ]
 
-
 parseGrouped :: Parser SaplingAST
 parseGrouped = between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) parseExpression
 
@@ -190,8 +196,8 @@ parseSingleItem = do
   token <- satisfy isListItem
   case token of
     LIdentifier name -> return (SVar name)
-    LKeywordT        -> return TLeaf
-    _                -> fail "Unexpected token in list item"
+    LKeywordT -> return TLeaf
+    _ -> fail "Unexpected token in list item"
 
 isListItem :: LToken -> Bool
 isListItem (LIdentifier _) = True
@@ -216,24 +222,19 @@ parseStrLiteral = do
   return (SStr value)
 
 -- Boolean Helpers
-isKeywordT       (LKeywordT)         = True
-isKeywordT                        _  = False
-
-isIdentifier     (LIdentifier     _) = True
-isIdentifier                      _  = False
-
+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
-
-esNewline        (LNewline)          = True
-isNewline                         _  = False
+isIntegerLiteral _ = False
+isStringLiteral (LStringLiteral _) = True
+isStringLiteral _ = False
+isLiteral (LIntegerLiteral _) = True
+isLiteral (LStringLiteral _) = True
+isLiteral _ = False
+isNewline (LNewline) = True
+isNewline _ = False
 
 -- Error Handling
 handleParseError :: ParseErrorBundle [LToken] Void -> String
@@ -246,9 +247,10 @@ handleParseError bundle =
 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)
+  ++ 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)
+  ++ show (Set.toList expected)
+