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)
}
--
Xiong, Yingfei (熊英飞)
Ph.D. Student
Institute of Software
School of Electronics Engineering and Computer Science
Peking University
Beijing, 100871, PRC.
Web: http://
xiong.yingfei.googlepages.com_________________________________________
______
Rob Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
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