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

Christian Maeder Christian.Maeder at dfki.de
Fri Feb 12 12:00:13 EST 2010

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


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.

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