[Haskell-cafe] On to applicative

michael rice nowgate at yahoo.com
Tue Aug 31 13:27:17 EDT 2010

So it's a type constructor, not a type? Could you please provide a simple example of its usage?


--- On Tue, 8/31/10, Vo Minh Thu <noteed at gmail.com> wrote:

From: Vo Minh Thu <noteed at gmail.com>
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice" <nowgate at yahoo.com>
Cc: haskell-cafe at haskell.org
Date: Tuesday, August 31, 2010, 1:17 PM

2010/8/31 michael rice <nowgate at yahoo.com>
> "Learn You a Haskell ..."  says that (->) is a type just like Either. Where can I find its type definition?

You can't define it *in* Haskell as user code. It is a built-in infix
type constructor (Either or Maybe are type constructors too, not just
types). In fact, if you want to implement a simple, typed functional
language, you'll find it is the only built-in type constructor you
have to implement (as the implementor of the language).

  Show a => a
is a type too, but you won't find a definition for 'a' or for '=>'.
All those things are defined by the language.


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