[Haskell-cafe] Re: Infix and postfix operators in Parsec

[Christian Maeder]

Parse a sequence of primitive expressions first and then do
fixity resolution independent from Parsec.

C.

Christian Maeder schrieb:
> It seems that the case of identical postfix and infix operators was not
> considered. So I recommend to write something from scratch.
> 
> Cheers Christian
> 
> Xinyu Jiang schrieb:
>> I'm writing a parser for a Haskell-style language, and when I need to
>> use the same symbol for infix, prefix and postfix operators, the
>> combinator "buildExpressionParser" seems not to work as intended. For
>> example, in:
>>
>> (1)x + y
>> (2)x +
>> (3)+ x
>>
>> If I set the priority of the postfix version of "+" to be higher than
>> the infix version, the parser cannot recognize (1), for it stops at the
>> end of "x +". And if the priority of postfix "+" is lower, Parsec
>> complains about (2) by returning an error message which expects
>> something after "+".
>>
>> Is there some way to get over this problem, and let me be able to still
>> benifit from the expression mechanism in Parsec. Or should I write these
>> stuff from scratch? Thanks.