Re: [Haskell-cafe] Operator precedence and associativity with Polyparse
Am 26.10.2011 01:49, schrieb Tom Hawkins: Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Do you mean parsing something like 1 + 2 * 3 ? I don't think there's any real difference in using Polyparse vs Parsec for this, except for doing p `orElse` q rather than try p| q. Actually, I was looking for something equivalent to Text.ParserCombinators.Parsec.Expr.buildExpressionParser. I suppose I should learn how Parsec implements this under the hood. I would do it as described under chainl1 in http://hackage.haskell.org/packages/archive/parsec2/1.0.0/doc/html/Text-ParserCombinators-Parsec-Combinator.html I believe Parsec.Expr cannot handle a prefix operator (i.e. unary minus) properly, that has lower precedence than an infix operator (i.e. ^ power). If it can parse -x^2 as -(x^2) then if cannot parse x^ -2 as x^(-2). Cheers Christian -Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Operator precedence and associativity with Polyparse
Hi, Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Thanks in advance. -Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence and associativity with Polyparse
On 26 October 2011 06:37, Tom Hawkins tomahawk...@gmail.com wrote: Hi, Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Do you mean parsing something like 1 + 2 * 3 ? I don't think there's any real difference in using Polyparse vs Parsec for this, except for doing p `orElse` q rather than try p | q. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence and associativity with Polyparse
Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Do you mean parsing something like 1 + 2 * 3 ? I don't think there's any real difference in using Polyparse vs Parsec for this, except for doing p `orElse` q rather than try p | q. Actually, I was looking for something equivalent to Text.ParserCombinators.Parsec.Expr.buildExpressionParser. I suppose I should learn how Parsec implements this under the hood. -Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence and associativity with Polyparse
On 26 October 2011 10:49, Tom Hawkins tomahawk...@gmail.com wrote: Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Do you mean parsing something like 1 + 2 * 3 ? I don't think there's any real difference in using Polyparse vs Parsec for this, except for doing p `orElse` q rather than try p | q. Actually, I was looking for something equivalent to Text.ParserCombinators.Parsec.Expr.buildExpressionParser. I suppose I should learn how Parsec implements this under the hood. There's nothing like that for PolyParse: it has a much smaller set of combinators than Parsec, which I for one prefer because I don't have to worry about behaviour of existing combinators being different than what I want/need (as it stands, I already use a custom version of bracket from polyparse). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Operator precedence
Is there a handy list of operators and their precedence somewhere? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
Take a look to the Haskell Report: http://www.haskell.org/onlinereport/haskell2010/haskellch9.html#x16-1710009 -- Daniel Díaz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
Thanks, Daniel. This be all of them? Michael infixr 9 . infixr 8 ^, ^^, ⋆⋆ infixl 7 ⋆, /, ‘quot‘, ‘rem‘, ‘div‘, ‘mod‘ infixl 6 +, - -- The (:) operator is built-in syntax, and cannot legally be given -- a fixity declaration; but its fixity is given by: -- infixr 5 : infix 4 ==, /=, , =, =, infixr 3 infixr 2 || infixl 1 , = infixr 1 = infixr 0 $, $!, ‘seq‘ --- On Mon, 9/6/10, Daniel Díaz lazy.dd...@gmail.com wrote: From: Daniel Díaz lazy.dd...@gmail.com Subject: Re: [Haskell-cafe] Operator precedence To: michael rice nowg...@yahoo.com, haskell-cafe@haskell.org Date: Monday, September 6, 2010, 1:06 PM Take a look to the Haskell Report: http://www.haskell.org/onlinereport/haskell2010/haskellch9.html#x16-1710009 -- Daniel Díaz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
Those are all operators in Prelude. See a concrete library for their operator precedences. -- Daniel Díaz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
A concrete library? I'm playing around with Data.Bits. It has .. and .|. which I assume are functions (rather than operators) because I don't see and infix statement for them. Correct? Michael --- On Mon, 9/6/10, Daniel Díaz lazy.dd...@gmail.com wrote: From: Daniel Díaz lazy.dd...@gmail.com Subject: Re: [Haskell-cafe] Operator precedence To: michael rice nowg...@yahoo.com, haskell-cafe@haskell.org Date: Monday, September 6, 2010, 1:17 PM Those are all operators in Prelude. See a concrete library for their operator precedences. -- Daniel Díaz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
Hello michael, Monday, September 6, 2010, 9:00:32 PM, you wrote: Is there a handy list of operators and their precedence somewhere? unlike most languages, operators are user-definable in haskell. so there is no comprehensive list any function with two arguments van be used as operator: a `min` b any operator may be defined or used as a function: () a b = ... main = print (() True False) -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
On Mon, Sep 6, 2010 at 1:37 PM, michael rice nowg...@yahoo.com wrote: A concrete library? I'm playing around with Data.Bits. It has .. and .|. which I assume are functions (rather than operators) because I don't see and infix statement for them. Correct? .|. and .. are operators because they are made from symbol characters. Operators default to infixl 9 unless specified otherwise, so no infix declaration is needed. However, Data.Bits does have infix declarations for .. and .|. : infixl 8 `shift`, `rotate`, `shiftL`, `shiftR`, `rotateL`, `rotateR` infixl 7 .. infixl 6 `xor` infixl 5 .|. If you want to check the fixity of an operator, use :info in GHCi. Prelude Data.Bits :i .|. class (Num a) = Bits a where ... (.|.) :: a - a - a ... -- Defined in Data.Bits infixl 5 .|. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
Hi David, You're right, I keep forgetting to look at the source code. And I wasn't aware of the info (:i) command. Should come in handy in the future. Michael --- On Mon, 9/6/10, David Menendez d...@zednenem.com wrote: From: David Menendez d...@zednenem.com Subject: Re: [Haskell-cafe] Operator precedence To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org, Daniel Díaz lazy.dd...@gmail.com Date: Monday, September 6, 2010, 1:50 PM On Mon, Sep 6, 2010 at 1:37 PM, michael rice nowg...@yahoo.com wrote: A concrete library? I'm playing around with Data.Bits. It has .. and .|. which I assume are functions (rather than operators) because I don't see and infix statement for them. Correct? .|. and .. are operators because they are made from symbol characters. Operators default to infixl 9 unless specified otherwise, so no infix declaration is needed. However, Data.Bits does have infix declarations for .. and .|. : infixl 8 `shift`, `rotate`, `shiftL`, `shiftR`, `rotateL`, `rotateR` infixl 7 .. infixl 6 `xor` infixl 5 .|. If you want to check the fixity of an operator, use :info in GHCi. Prelude Data.Bits :i .|. class (Num a) = Bits a where ... (.|.) :: a - a - a ... -- Defined in Data.Bits infixl 5 .|. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
El Lun, 6 de Septiembre de 2010, 7:50 pm, David Menendez escribió: Operators default to infixl 9 unless specified otherwise, so no infix declaration is needed. Why there is a default infix? Why it is 9? -- Daniel Díaz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Operator precedence
On Mon, Sep 6, 2010 at 2:21 PM, Daniel Díaz danield...@asofilak.es wrote: El Lun, 6 de Septiembre de 2010, 7:50 pm, David Menendez escribió: Operators default to infixl 9 unless specified otherwise, so no infix declaration is needed. Why there is a default infix? Why it is 9? That's what the Haskell Report says: Any operator lacking a fixity declaration is assumed to be infixl 9 (section 4.4.2). Any function with at least two arguments can be used as an operator, so there has to be a default. Presumably, infixl 9 was considered the least surprising. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Operator precedence and associativity on happy grammars
Hello.
I am learning how to use Happy (a LALR(1) parser generator) and I have a
question on a grammar based on an example from the manual. The input
file to Happy is attached to this message.
The grammar is:
Exp - let var = Exp in Exp
Exp - Exp + Exp
Exp - Exp - Exp
Exp - Exp * Exp
Exp - Exp / Exp
Exp - ( Exp )
This grammar is ambiguous, but the conflicts that will appear in the
parser table can be resolved with precedence and associativity
declarations for the operators that surround expressions:
%right in
%left + -
%left * /
giving right associativity to the in token, and left associativity to
the arithmetic operators, and giving lower precedence to in, followed by
+ and -, and then by * and /.
I see that if the token in is not given a precedence declaration, the
grammar still is ambiguous, as can be seen in the example of parsing the
expression:
let v = e1 in e2 + e3
which could be parsed as
(let v = e1 in e2) + e3
or
let v = e1 in (e2 + e3)
Giving the token in a lower precedence makes the parser choose the last
option.
My question is about the associativity of the token in? Does it make any
difference giving it left associativity, right associativity, or making
it non associative?
Regards.
José Romildo
-- calc3.y-*- mode: haskell -*-
{
module Main where
import Data.Char (isSpace, isDigit, isAlpha, isAlphaNum)
import Data.Maybe (fromMaybe)
}
%name calc
%tokentype { Token }
%error { parseError }
%token
let { TokenLet }
in { TokenIn }
int { TokenInt $$ }
var { TokenVar $$ }
'=' { TokenEq }
'+' { TokenPlus }
'-' { TokenMinus }
'*' { TokenTimes }
'/' { TokenDiv }
'(' { TokenLP }
')' { TokenRP }
%nonassoc in
%left '+' '-'
%left '*' '/'
%left NEG
%%
Exp : let var '=' Exp in Exp { \env - $6 (($2,$4 env) : env) }
| Exp '+' Exp{ \env - $1 env + $3 env }
| Exp '-' Exp{ \env - $1 env - $3 env }
| Exp '*' Exp{ \env - $1 env * $3 env }
| Exp '/' Exp{ \env - $1 env `div` $3 env }
| '(' Exp ')'{ $2 }
| '-' Exp %prec NEG { \env - - ($2 env) }
| int{ \env - $1 }
| var{ \env - fromMaybe 0 (lookup $1 env) }
{
parseError :: [Token] - a
parseError _ = error Parse error
data Token
= TokenLet
| TokenIn
| TokenInt Int
| TokenVar String
| TokenEq
| TokenPlus
| TokenMinus
| TokenTimes
| TokenDiv
| TokenLP
| TokenRP
deriving (Show)
lexer :: String - [Token]
lexer [] = []
lexer (c:cs) | isSpace c = lexer cs
| isAlpha c = let (name,rest) = span isAlphaNum cs
tok = case c:name of
let - TokenLet
in - TokenIn
var - TokenVar var
in tok : lexer rest
| isDigit c = let (num,rest) = span isDigit cs
in TokenInt (read (c:num)) : lexer rest
lexer ('=':cs) = TokenEq: lexer cs
lexer ('+':cs) = TokenPlus : lexer cs
lexer ('-':cs) = TokenMinus : lexer cs
lexer ('*':cs) = TokenTimes : lexer cs
lexer ('/':cs) = TokenDiv : lexer cs
lexer ('(':cs) = TokenLP: lexer cs
lexer (')':cs) = TokenRP: lexer cs
main = do input - getContents
mapM_ print (map (($ []) . calc . lexer) (lines input))
}
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