On Aug 25, 2006, at 6:27 AM, Xiong Yingfei wrote:
Hi,
I am trying out Alex. I copied the calculator specification file from Alex's official document and changed the wrapper type from "basic" to "monad". However, after I generated the ".hs" file from the lexical specification and compiled the ".hs" file, I got the message "Variable not in scope: `alexEOF'". I cannot find explanation about this 'alexEOF' function in the document. Can any body be kindly enough to tell me what this function is? Should I write it myself or not? My lexical code is listed as the below. Thanks a lot.
You should provide alexEOF. The idea is that it is a special token representing the end of input. This is necessary because the monad wrapper doesn't deliver a list of tokens like the basic wrapper, so it needs some way to signal the end of input. The easiest thing to do is add a constructor to your token datatype, and then just set alexEOF to that constructor: data Token = .... | EOFToken alexEOF = EOFToken
{ module Lex where
}
%wrapper "monad"
$digit = 0-9 -- digits $alpha = [a-zA-Z] -- alphabetic characters
tokens :-
$white+ ; "--".* ; let { \s -> Let } in { \s -> In } $digit+ { \s -> Int (read s) } [\=\+\-\*\/\(\)] { \s -> Sym (head s) } $alpha [$alpha $digit \_ \']* { \s -> Var s }
{ -- Each action has type :: String -> Token
-- The token type: data Token = Let | In | Sym Char | Var String | Int Int deriving (Eq,Show) }
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