Additional test cases and bug fixes for subtle issues

src/Parser.hs

@@ -20,6 +20,7 @@ data SaplingAST
   deriving (Show, Eq, Ord)
 
 parseSapling :: String -> SaplingAST
+parseSapling "" = error "Empty input provided to parseSapling"
 parseSapling input = case runParser parseExpression "" (lexSapling input) of
   Left err -> error "Failed to parse input"
   Right ast -> ast
@@ -122,8 +123,14 @@ parseListLiteral = do
   satisfy (== LCloseBracket)
   return (SList elements)
 
+--parseListItem :: Parser SaplingAST
+--parseListItem = parseGroupedItem <|> parseSingleItem
 parseListItem :: Parser SaplingAST
-parseListItem = parseGroupedItem <|> parseSingleItem
+parseListItem = choice
+  [ parseGroupedItem  -- Handle expressions inside parentheses
+  , parseListLiteral  -- Allow nested lists
+  , parseSingleItem   -- Handle single tokens like `t` or identifiers
+  ]
 
 parseGroupedItem :: Parser SaplingAST
 parseGroupedItem = do

test/Spec.hs

@@ -5,6 +5,7 @@ import Lexer
 import Parser
 import Research
 
+import Control.Exception (evaluate, try, SomeException)
 import qualified Data.Map as Map
 import Test.Tasty
 import Test.Tasty.HUnit
@@ -58,6 +59,27 @@ parserTests = testGroup "Parser Tests"
       let input = "t t t"
       let expected = TFork TLeaf TLeaf
       parseSapling input @?= expected
+
+  , testCase "Parse mixed list literals" $ do
+      -- You must put non-listliterals in parentheses
+      let input = "[t (\"hello\") t]" 
+      let expected = SList [TLeaf, SStr "hello", TLeaf]
+      parseSapling input @?= expected
+
+  , testCase "Parse function with applications" $ do
+      let input = "f x = t x"
+      let expected = SFunc "f" ["x"] (SApp TLeaf [SVar "x"])
+      parseSapling input @?= expected
+
+  , testCase "Parse nested lists" $ do
+      let input = "[t [(t t)]]"
+      let expected = SList [TLeaf, SList [TStem TLeaf]]
+      parseSapling input @?= expected
+
+  , testCase "Parse complex parentheses" $ do
+      let input = "t (t t (t t))"
+      let expected = TStem (TFork TLeaf (TStem TLeaf))
+      parseSapling input @?= expected
   ]
 
 integrationTests :: TestTree
@@ -138,4 +160,3 @@ propertyTests = testGroup "Property Tests"
           Left _ -> property True
           Right ast -> parseSapling input === ast
   ]
-