[Haskell-cafe] Function application like a Unix pipe

Scherrer, Chad Chad.Scherrer at pnl.gov
Wed Nov 23 12:01:07 EST 2005

Udo Stenzel <u.stenzel at web.de> writes:

> The unix pipe is actually function composition.  Its argument 
> (standard
> input) isn't explicitly mentioned

Then it seems Unix must overload the "|" operator. I typically use it to
do things like
grep "." *.hs | wc

So I think of the types as being 
grep "." *.hs :: String
wc :: String -> Int  -- ok, not really, but it shows the point better.

So we'd have to have 
(|) :: a -> (a -> b) -> b

And (flip ($)) is the only thing that makes sense. Is it the case that a
Unix pipe is analagous to (flip ($)) or (flip (.)) depending on the

Chad Scherrer
Computational Mathematics Group
Pacific Northwest National Laboratory

"Time flies like an arrow; fruit flies like a banana." -- Groucho Marx 

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