Initialize Repo

Working (but likely buggy!) lexing, parsing, and evaluation of Tree Calculus terms

src/Lexer.hs

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+module Lexer where
+
+import Research
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import Data.Void
+
+type Lexer = Parsec Void String
+data LToken
+  = LKeywordT
+  | LIdentifier String
+  | LIntegerLiteral Int
+  | LStringLiteral String
+  | LAssign
+  | LOpenParen
+  | LCloseParen
+  | LOpenBracket
+  | LCloseBracket
+  | LNewline
+  deriving (Show, Eq, Ord)
+
+keywordT :: Lexer LToken
+keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT
+
+identifier :: Lexer LToken
+identifier = do
+  name <- some (letterChar <|> char '_' <|> char '-')
+  if name == "t"
+    then fail "Keyword 't' cannot be used as an identifier"
+    else return (LIdentifier name)
+
+integerLiteral :: Lexer LToken
+integerLiteral = do
+  num <- some digitChar
+  return (LIntegerLiteral (read num))
+
+stringLiteral :: Lexer LToken
+stringLiteral = do
+  char '"'
+  content <- many (noneOf ['"'])
+  char '"' --"
+  return (LStringLiteral content)
+
+assign :: Lexer LToken
+assign = char '=' *> pure LAssign
+
+openParen :: Lexer LToken
+openParen = char '(' *> pure LOpenParen
+
+closeParen :: Lexer LToken
+closeParen = char ')' *> pure LCloseParen
+
+openBracket :: Lexer LToken
+openBracket = char '[' *> pure LOpenBracket
+
+closeBracket :: Lexer LToken
+closeBracket = char ']' *> pure LCloseBracket
+
+lnewline :: Lexer LToken
+lnewline = char '\n' *> pure LNewline
+
+sc :: Lexer ()
+sc = skipMany (char ' ' <|> char '\t')
+
+saplingLexer :: Lexer [LToken]
+saplingLexer = many (sc *> choice
+  [ try keywordT
+  , try identifier
+  , try integerLiteral
+  , try stringLiteral
+  , assign
+  , openParen
+  , closeParen
+  , openBracket
+  , closeBracket
+  , lnewline
+  ]) <* eof