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Today's Topics:
1. Happy generated parser fails to compile. (Rohit Garg)
2. Re: Happy generated parser fails to compile. (Stephen Tetley)
----------------------------------------------------------------------
Message: 1
Date: Sun, 26 Sep 2010 20:28:05 +0530
From: Rohit Garg <[email protected]>
Subject: [Haskell-beginners] Happy generated parser fails to compile.
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
Hi,
Following is a simple parser definition I am trying to write for
simple numerical expressions. A sequence of numerical expressions
actually. Happy reports that there are 3 un-used terminals. AFAIK,
they should be let, in and '='. Is that correct?
Although, happy generates a .hs file without any other message. GHC
gives a type mismatch error. I don't suppose it could be a lexer
error, could it?
a) Could this be a bug in Happy (very unlikely, IMO) it is generating
code that has type mismatches.
b) If there is a bug in my parser definition, shouldn't Happy beep on it?
Any suggestions to fix it will be highly appreciated.
Thanks,
===================
{
module Main where
import Tokens_posn
}
%name calc
%tokentype { Token }
%token let { Let _ }
in { In _ }
';' { Newstatement _ }
int { Int _ $$ }
var { Var _ $$ }
'=' { Sym _ '=' }
'+' { Sym _ '+' }
'-' { Sym _ '-' }
'*' { Sym _ '*' }
'/' { Sym _ '/' }
'(' { Sym _ '(' }
')' { Sym _ ')' }
%%
Exprs :: { [ Expr ] }
Exprs : Exprs Expr ';' { $2 : $1 }
| Expr ';' { [$1] }
Expr : Expr '+' Term { PlusE $1 $3 }
| Expr '-' Term { MinusE $1 $3 }
| Term { $1 }
Term : Term '*' Factor { TimesE $1 $3 }
| Term '/' Factor { DivE $1 $3 }
| Factor { $1 }
Factor : '-' Atom { NegE $2 }
| Atom { $1 }
Atom : int { IntE $1 }
| var { VarE $1 }
| '(' Expr ')' { $2 }
{
data Expr =
LetE String Expr Expr |
PlusE Expr Expr |
MinusE Expr Expr |
TimesE Expr Expr |
DivE Expr Expr |
NegE Expr |
IntE Int |
VarE String
deriving Show
flist :: [Int] -> Int -> [Int]
flist x a = a : x
main:: IO ()
main = interact (show.runCalc)
runCalc :: String -> Expr
runCalc = calc . alexScanTokens
happyError :: [Token] -> a
happyError tks = error ("Parse error at " ++ lcn ++ "\n")
where
lcn = case tks of
[] -> "end of file"
tk:_ -> "line " ++ show l ++ ", column " ++ show c
where
AlexPn _ l c = token_posn tk
}
--
Rohit Garg
http://rpg-314.blogspot.com/
------------------------------
Message: 2
Date: Sun, 26 Sep 2010 17:16:09 +0100
From: Stephen Tetley <[email protected]>
Subject: Re: [Haskell-beginners] Happy generated parser fails to
compile.
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
Hello
If you run happy with the info option and a file name for the output,
happy will produce a report on the grammar:
> happy -info=INFO.txt Main.g
You are right that the three unused termianls are 'let' 'in' and '='
terminal let is unused
terminal in is unused
terminal '=' is unused
You are also importing a file Tokens_posn (presumably the lexer?)
which you haven't posted - without being able to see this or the
actual error message its rather hard to decode the error, however if
you are using the file Token_posn.x from the Alex distribution there
are two problems - one is you need Newstatement as a token, the other
is runCalc has this type:
runCalc :: String -> [Expr]
runCalc ss = calc $ alexScanTokens ss
Best wishes
Stephen
------------------------------
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