Re: [Haskell-cafe] Operator precedence and associativity with Polyparse

[Christian Maeder]

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


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Re: [Haskell-cafe] Operator precedence and associativity with Polyparse

[Ivan Lazar Miljenovic]

On 26 October 2011 10:49, Tom Hawkins  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

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Re: [Haskell-cafe] Operator precedence and associativity with Polyparse

[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.

-Tom

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Re: [Haskell-cafe] Operator precedence and associativity with Polyparse

[Ivan Lazar Miljenovic]

On 26 October 2011 06:37, Tom Hawkins  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

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Re: [Haskell-cafe] Operator precedence

[David Menendez]

On Mon, Sep 6, 2010 at 2:21 PM, Daniel Díaz  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 

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Re: [Haskell-cafe] Operator precedence

[Daniel Díaz]

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

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Re: [Haskell-cafe] Operator precedence

[michael rice]

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  wrote:

From: David Menendez 
Subject: Re: [Haskell-cafe] Operator precedence
To: "michael rice" 
Cc: haskell-cafe@haskell.org, "Daniel Díaz" 
Date: Monday, September 6, 2010, 1:50 PM

On Mon, Sep 6, 2010 at 1:37 PM, michael rice  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 
<http://www.eyrie.org/~zednenem/>



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Re: [Haskell-cafe] Operator precedence

[David Menendez]

On Mon, Sep 6, 2010 at 1:37 PM, michael rice  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 

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Re: [Haskell-cafe] Operator precedence

[Bulat Ziganshin]

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

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Re: [Haskell-cafe] Operator precedence

[michael rice]

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  wrote:

From: Daniel Díaz 
Subject: Re: [Haskell-cafe] Operator precedence
To: "michael rice" , 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




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Re: [Haskell-cafe] Operator precedence

[Daniel Díaz]

Those are all operators in Prelude. See a concrete library for their
operator precedences.

-- 
Daniel Díaz
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Re: [Haskell-cafe] Operator precedence

[michael rice]

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  wrote:

From: Daniel Díaz 
Subject: Re: [Haskell-cafe] Operator precedence
To: "michael rice" , 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




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Re: [Haskell-cafe] Operator precedence

[Daniel Díaz]

Take a look to the Haskell Report:

http://www.haskell.org/onlinereport/haskell2010/haskellch9.html#x16-1710009

-- 
Daniel Díaz
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