File: tokens_gscan.x

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{
module Main (main) where
import System.Exit
}

%wrapper "gscan"

$digit = 0-9			-- digits
$alpha = [a-zA-Z]		-- alphabetic characters

tokens :-

  $white+				;
  "--".*				;
  let					{ tok (\p s -> Let p) }
  in					{ tok (\p s -> In p) }
  $digit+				{ tok (\p s -> Int p (read s)) }
  [\=\+\-\*\/\(\)]			{ tok (\p s -> Sym p (head s)) }
  $alpha [$alpha $digit \_ \']*		{ tok (\p s -> Var p s) }

{
-- Some action helpers:
tok f p c str len cont (sc,state) = f p (take len str) : cont (sc,state)

-- The token type:
data Token =
	Let AlexPosn		|
	In  AlexPosn		|
	Sym AlexPosn Char	|
	Var AlexPosn String	|
	Int AlexPosn Int	|
	Err AlexPosn
	deriving (Eq,Show)

main = if test1 /= result1 then exitFailure
			   else exitWith ExitSuccess

test1 = alexGScan stop undefined "  let in 012334\n=+*foo bar__'"

stop p c "" (sc,s) = []
stop p c _  (sc,s) = error "lexical error"

result1 = [Let (AlexPn 2 1 3),In (AlexPn 6 1 7),Int (AlexPn 9 1 10) 12334,Sym (AlexPn 16 2 1) '=',Sym (AlexPn 17 2 2) '+',Sym (AlexPn 18 2 3) '*',Var (AlexPn 19 2 4) "foo",Var (AlexPn 23 2 8) "bar__'"]
}