Lexer.x

{
{-# LANGUAGE FlexibleContexts #-}

module Language.Nano.Lexer (
  Token(..),
  scanTokens
) where

import Control.Monad.Except

}

%wrapper "posn"

$digit = 0-9
$alpha = [a-zA-Z]
$eol   = [\n]

tokens :-

  -- Whitespace insensitive
  $eol                          ;
  $white+                       ;

  -- Comments
  "#".*                         ;

  ------------------------------------------------------------------------------
  -- Syntax  [ THIS IS THE ONLY SEGMENT YOU NEED TO CHANGE ]

  in                            { \p _ -> IN     p }
  "&&"                          { \p _ -> AND    p }
  \(                            { \p _ -> LPAREN p }
  \)                            { \p _ -> RPAREN p }
  \:                            { \p _ -> COLON  p }
  \,                            { \p _ -> COMMA  p }

  -- DO NOT CHANGE ANYTHING AFTER THIS LINE ------------------------------------
  ------------------------------------------------------------------------------
{

data Token
  = LET    AlexPosn
  | TRUE   AlexPosn
  | FALSE  AlexPosn
  | IN     AlexPosn
  | IF     AlexPosn
  | THEN   AlexPosn
  | ELSE   AlexPosn
  | AND    AlexPosn
  | OR     AlexPosn
  | LESS   AlexPosn
  | LEQ    AlexPosn
  | NEQ    AlexPosn
  | LAM    AlexPosn
  | NUM    AlexPosn Int
  | ID     AlexPosn String
  | ARROW  AlexPosn
  | EQB    AlexPosn
  | EQL    AlexPosn
  | PLUS   AlexPosn
  | MINUS  AlexPosn
  | MUL    AlexPosn
  | LPAREN AlexPosn
  | RPAREN AlexPosn
  | LBRAC  AlexPosn
  | RBRAC  AlexPosn
  | COLON  AlexPosn
  | COMMA  AlexPosn
  | EOF    AlexPosn
  deriving (Eq,Show)


getLineNum :: AlexPosn -> Int
getLineNum (AlexPn _ lineNum _) = lineNum

getColumnNum :: AlexPosn -> Int
getColumnNum (AlexPn _ _ colNum) = colNum

scanTokens :: String -> Except String [Token]
scanTokens str = go (alexStartPos,'\n',[],str)
  where
    go inp@(pos,_,_,str) =
      case alexScan inp 0 of
        AlexEOF -> return []
        AlexError ((AlexPn _ line column),_,_,_) -> throwError $ "lexical error at " ++ (show line) ++ " line, " ++ (show column) ++ " column"
        AlexSkip  inp' _       -> go inp'
        AlexToken inp' len act -> do
          res <- go inp'
          let rest = act pos (take len str)
          return (rest : res)

}