[Haskell-cafe] Where does ~> come from?

Wolfgang Jeltsch g9ks157k at acme.softbase.org
Tue Feb 19 05:22:22 EST 2008

Am Sonntag, 17. Februar 2008 14:41 schrieb Neil Mitchell:
> Hi
> > 2) You would hope there is a quick way to search those symbols. But
> > most search engines do not treate symbols friendly, often just ignore
> > them. I typed ~> in Hoogle, it also returned nothing.
> > 3) If the module defining the symbol is not in standard library, it is
> > not possible to look up the symbol in the core library index.
> The next version of Hoogle will allow you to search all the modules on
> Hackage, i.e. it will find ~>. A month after I have written my thesis
> this will all be done :-)
> Thanks
> Neil

I think, it won’t find it.  As Cale said, it’s a type variable.  It’s like 
the “a” in the following definition:

    data T a = T a a

I think, Conal Elliott used an operator type variable in order to make his 
code more readable.  The (~>) is a type parameter which stands for an arrow 

Best wishes,

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