0.2.0

Includes better error handling, additional tests, parsing and lexing
fixes to match the desired behavior defined by the new tests, and a very
basic REPL implementation.

src/Lexer.hs

@@ -4,7 +4,9 @@ import Research
 import Text.Megaparsec
 import Text.Megaparsec.Char
 import Data.Void
+import qualified Data.Set as Set
 
+-- Lexer type and tokens
 type Lexer = Parsec Void String
 data LToken
   = LKeywordT
@@ -19,6 +21,7 @@ data LToken
   | LNewline
   deriving (Show, Eq, Ord)
 
+-- Lexical rules
 keywordT :: Lexer LToken
 keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT
 
@@ -38,8 +41,11 @@ stringLiteral :: Lexer LToken
 stringLiteral = do
   char '"'
   content <- many (noneOf ['"'])
-  char '"' --"
-  return (LStringLiteral content)
+  if null content
+    then fail "Empty string literals are not allowed"
+    else do
+      char '"' -- "
+      return (LStringLiteral content)
 
 assign :: Lexer LToken
 assign = char '=' *> pure LAssign
@@ -59,13 +65,15 @@ closeBracket = char ']' *> pure LCloseBracket
 lnewline :: Lexer LToken
 lnewline = char '\n' *> pure LNewline
 
+-- Whitespace consumer
 sc :: Lexer ()
 sc = skipMany (char ' ' <|> char '\t')
 
+-- Lexer definition
 saplingLexer :: Lexer [LToken]
 saplingLexer = many (sc *> choice
-  [ try keywordT
-  , try identifier
+  [ try identifier
+  , try keywordT
   , try integerLiteral
   , try stringLiteral
   , assign
@@ -74,8 +82,10 @@ saplingLexer = many (sc *> choice
   , openBracket
   , closeBracket
   , lnewline
-  ]) <* eof
+  ] <* sc) <* eof
 
+-- Lexing function with enhanced error handling
+lexSapling :: String -> [LToken]
 lexSapling input = case runParser saplingLexer "" input of
-  Left err -> error "Failed to lex input"
+  Left err  -> error $ "Lexical error:\n" ++ errorBundlePretty err
   Right tokens -> tokens