[Haskell-cafe] Function application like a Unix pipe

Henning Thielemann lemming at henning-thielemann.de
Wed Nov 23 11:47:03 EST 2005

On Wed, 23 Nov 2005, Scherrer, Chad wrote:

> Henning Thielemann <lemming at henning-thielmann.de> writes:
>> Since
>>   (a . b) x
>>   a $ b x
>>   a (b x)
>> are equivalent, do you also want to reverse function and
>> argument in order to match argument order of . and $ ?
>> That is
>>   x (b . a)
>>   x b $ a
>>   (x b) a
>> ?
> I'm sorry, I'm not sure I understand your question. Are you asking
> whether one should be allowed to write x f instead of f x? I don't think
> anyone is advocating this, but is can be convenient to have an infix
> operator for this purpose.

  I want to say, that the order of symbols for ($), (.) and function 
application is consistent. This is a fine thing. I think that shall not be 
distroyed by giving ($) and (.) reversed argument order.

  It's of course a good question, why (>>) and (>>=) have the opposite 
order of (.). Compare function application
  a b
   where a is applied to b with the monadic case
  b >>= a
   where a is applied to the result of b. This makes changing a non-monadic 
expression to a similar monadic expression more difficult.
  Why is there no (<<) and why is (=<<) not the default? The order of 'do 
{a;b;c}' is compatible with that of (>>). So we have the fundamental 
conflict, that usually function application is from right to left, but 
interpreting imperative statements is from left to right.
  I think that's a similar conflict like that of little endian and big 

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