0.1.0 base collection of features

Implemented evaluation of tree calculus terms alongside referentially
transparent variable identifiers. Implemented evaluation of defined
functions into tree calculus.

src/Parser.hs

@@ -20,11 +20,9 @@ data SaplingAST
   deriving (Show, Eq, Ord)
 
 parseSapling :: String -> SaplingAST
-parseSapling input = case runParser saplingLexer "" input of
-  Left err -> error "RIP"
-  Right tokens -> case runParser parseExpression "" tokens of
-    Left err -> error "RIP"
-    Right ast -> ast
+parseSapling input = case runParser parseExpression "" (lexSapling input) of
+  Left err -> error "Failed to parse input"
+  Right ast -> ast
 
 scnParser :: Parser ()
 scnParser = skipMany (satisfy isNewline)
@@ -48,9 +46,26 @@ parseFunction = do
 
 parseApplication :: Parser SaplingAST
 parseApplication = do
-  func <- parseAtomic
+  func <- parseAtomicBase
   args <- many parseAtomic
-  return (SApp func args)
+  case func of
+    TLeaf | not (null args) && all isTreeTerm args -> fail "Not an application, defer to Tree Calculus"
+    _ -> return (SApp func args)
+
+isTreeTerm :: SaplingAST -> Bool
+isTreeTerm TLeaf = True
+isTreeTerm (TStem _) = True
+isTreeTerm (TFork _ _) = True
+isTreeTerm _ = False
+
+parseAtomicBase :: Parser SaplingAST
+parseAtomicBase = choice
+  [ parseVar
+  , parseTreeLeaf
+  ]
+
+parseTreeLeaf :: Parser SaplingAST
+parseTreeLeaf = satisfy isKeywordT *> pure TLeaf
 
 getIdentifier :: LToken -> String
 getIdentifier (LIdentifier name) = name
@@ -81,6 +96,7 @@ foldTree (x:y:rest) = TFork x (foldTree (y:rest))
 parseAtomic :: Parser SaplingAST
 parseAtomic = choice
   [ parseVar
+  , parseTreeLeafOrParenthesized
   , parseLiteral
   , parseListLiteral
   , between (satisfy (== LOpenParen)) (satisfy (== LCloseParen)) parseExpression
@@ -92,13 +108,43 @@ parseLiteral = choice
   , parseStrLiteral
   ]
 
+parens :: Parser SaplingAST -> Parser SaplingAST
+parens p = do
+  satisfy (== LOpenParen)
+  result <- p
+  satisfy (== LCloseParen)
+  return result
+
 parseListLiteral :: Parser SaplingAST
 parseListLiteral = do
-  satisfy (== LOpenBracket) 
-  elements <- sepEndBy parseExpression scnParser
+  satisfy (== LOpenBracket)
+  elements <- many parseListItem
   satisfy (== LCloseBracket)
   return (SList elements)
 
+parseListItem :: Parser SaplingAST
+parseListItem = parseGroupedItem <|> parseSingleItem
+
+parseGroupedItem :: Parser SaplingAST
+parseGroupedItem = do
+  satisfy (== LOpenParen) 
+  inner <- parseExpression
+  satisfy (== LCloseParen)
+  return inner
+
+parseSingleItem :: Parser SaplingAST
+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 SaplingAST
 parseVar = do 
   LIdentifier name <- satisfy isIdentifier
@@ -114,6 +160,12 @@ parseStrLiteral = do
   LStringLiteral value <- satisfy isStringLiteral
   return (SStr value)
 
+parseMulti :: String -> [SaplingAST]
+parseMulti input =
+  let nonEmptyLines = filter (not . null) (lines input) 
+  in map parseSapling nonEmptyLines
+
+-- Boolean Helpers
 isKeywordT       (LKeywordT)         = True
 isKeywordT                        _  = False
 
@@ -128,4 +180,3 @@ isStringLiteral                   _  = False
 
 isNewline        (LNewline)          = True
 isNewline                         _  = False
-