how to see operators precedence in GHCi

[Bulat Ziganshin-2]

Hello ,

from http://community.livejournal.com/ru_declarative/54566.html

Q: how to see operators precedence in GHCi?
A:
Prelude> let showParen = (undefined::[[[[()]]]]->())
Prelude> showParen $ 2+3*4
<interactive>:1:12:
    No instance for (Num [[[[()]]]])
      arising from use of `+' at <interactive>:1:12
    Probable fix: add an instance declaration for (Num [[[[()]]]])
    In the second argument of `($)', namely `2 + (3 * 4)'
    In the definition of `it': it = showParen $ (2 + (3 * 4))
Prelude>

--
Best regards,
 Bulat                          mailto:Bulat.Ziganshin@...

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[Jon Fairbairn]

Bulat Ziganshin <bulat.ziganshin@...> writes:

> Hello ,
>
> from http://community.livejournal.com/ru_declarative/54566.html
>
> Q: how to see operators precedence in GHCi?
> A:
> Prelude> let showParen = (undefined::[[[[()]]]]->())
> Prelude> showParen $ 2+3*4
> <interactive>:1:12:
>     No instance for (Num [[[[()]]]])
>       arising from use of `+' at <interactive>:1:12
>     Probable fix: add an instance declaration for (Num [[[[()]]]])
>     In the second argument of `($)', namely `2 + (3 * 4)'
>     In the definition of `it': it = showParen $ (2 + (3 * 4))

Hmm, OK, but not that much quicker than going
   Prelude> :info (*)
   class (Eq a, Show a) => Num a where
     ...
     (*) :: a -> a -> a
     ...
           -- Defined in GHC.Num
   infixl 7 *
   Prelude>  :info (+)
   class (Eq a, Show a) => Num a where
     (+) :: a -> a -> a
     ...
           -- Defined in GHC.Num
   infixl 6 +
   Prelude>


--
Jón Fairbairn                                 Jon.Fairbairn@...

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[Bulat Ziganshin-2]

Hello Jon,

Wednesday, July 25, 2007, 8:07:57 PM, you wrote:
>> Q: how to see operators precedence in GHCi?
>>     In the definition of `it': it = showParen $ (2 + (3 * 4))

> Hmm, OK, but not that much quicker than going
>    Prelude> :info (*)

it just my poor english :)  i mean - "how to see how Haskell will
parse some expression?". it will be too slow to look up each
precedence and parse expression by hand :)

--
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@...

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[Stefan O'Rear]

On Wed, Jul 25, 2007 at 09:35:38PM +0400, Bulat Ziganshin wrote:

> Hello Jon,
>
> Wednesday, July 25, 2007, 8:07:57 PM, you wrote:
> >> Q: how to see operators precedence in GHCi?
> >>     In the definition of `it': it = showParen $ (2 + (3 * 4))
>
> > Hmm, OK, but not that much quicker than going
> >    Prelude> :info (*)
>
> it just my poor english :)  i mean - "how to see how Haskell will
> parse some expression?". it will be too slow to look up each
> precedence and parse expression by hand :)

Much easier:

stefan@stefans:~$ ghci
GHCi, version 6.7.20070712: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> :set -ddump-parsed
Prelude> 2 + 3 * 4

==================== Parser ====================
Just (2 + 3) * 4


14
Prelude>

Stefan


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[Stefan O'Rear]

On Wed, Jul 25, 2007 at 10:55:56AM -0700, Stefan O'Rear wrote:

> On Wed, Jul 25, 2007 at 09:35:38PM +0400, Bulat Ziganshin wrote:
> > Hello Jon,
> >
> > Wednesday, July 25, 2007, 8:07:57 PM, you wrote:
> > >> Q: how to see operators precedence in GHCi?
> > >>     In the definition of `it': it = showParen $ (2 + (3 * 4))
> >
> > > Hmm, OK, but not that much quicker than going
> > >    Prelude> :info (*)
> >
> > it just my poor english :)  i mean - "how to see how Haskell will
> > parse some expression?". it will be too slow to look up each
> > precedence and parse expression by hand :)
>
> Much easier:
>
> stefan@stefans:~$ ghci
> GHCi, version 6.7.20070712: http://www.haskell.org/ghc/  :? for help
> Loading package base ... linking ... done.
> Prelude> :set -ddump-parsed
> Prelude> 2 + 3 * 4
>
> ==================== Parser ====================
> Just (2 + 3) * 4
>
>
> 14
> Prelude>

Uhm...  that didn't work :)

Not quite as nice:

stefan@stefans:~$ ghci -ddump-rn-trace
GHCi, version 6.7.20070712: http://www.haskell.org/ghc/  :? for help
Top level:
    tcRnStmt let __cmCompileExpr = System.IO.stdout
             let __cmCompileExpr = GHC.Handle.stdout
             [(rw, GHC.Handle.stdout)]
Loading package base ... linking ... done.
Top level:
    tcRnStmt let __cmCompileExpr = System.IO.stderr
             let __cmCompileExpr = GHC.Handle.stderr
             [(rjJ, GHC.Handle.stderr)]
Top level:
    tcRnStmt let __cmCompileExpr = System.IO.stdin
             let __cmCompileExpr = GHC.Handle.stdin
             [(rq, GHC.Handle.stdin)]
Prelude> 2 + 3 * 4
Top level:
    tcRnStmt (2 + 3) * 4
             2 + (3 * 4)
           [(rqz, +), (rqA, *)]
14
Prelude>

Stefan


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[Simon Peyton-Jones]

| Uhm...  that didn't work :)
|
| Not quite as nice:
|
| stefan@stefans:~$ ghci -ddump-rn-trace

You probably wanted -ddump-rn

Simon
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[Stefan O'Rear]

On Thu, Jul 26, 2007 at 12:42:52AM +0100, Simon Peyton-Jones wrote:
>
> | Uhm...  that didn't work :)
> |
> | Not quite as nice:
> |
> | stefan@stefans:~$ ghci -ddump-rn-trace
>
> You probably wanted -ddump-rn

Seemed so, but that option has no effect (bug?):

stefan@stefans:~$ ghci -ddump-rn
GHCi, version 6.7.20070712: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> 2 + 2
4
Prelude>

Stefan


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[Simon Peyton-Jones]

Hmm. Good point.  Fixed.

Smion

| -----Original Message-----
| From: Stefan O'Rear [mailto:stefanor@...]
| Sent: 26 July 2007 01:01
| To: Simon Peyton-Jones
| Cc: Bulat Ziganshin; haskell-cafe@...; Jon Fairbairn
| Subject: Re: [Haskell-cafe] Re: how to see operators precedence in GHCi
|
| On Thu, Jul 26, 2007 at 12:42:52AM +0100, Simon Peyton-Jones wrote:
| >
| > | Uhm...  that didn't work :)
| > |
| > | Not quite as nice:
| > |
| > | stefan@stefans:~$ ghci -ddump-rn-trace
| >
| > You probably wanted -ddump-rn
|
| Seemed so, but that option has no effect (bug?):
|
| stefan@stefans:~$ ghci -ddump-rn
| GHCi, version 6.7.20070712: http://www.haskell.org/ghc/  :? for help
| Loading package base ... linking ... done.
| Prelude> 2 + 2
| 4
| Prelude>
|
| Stefan
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