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POAre there "type-level combinators"? Will they exist in some future?
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2011-11-23T19:49:34.983
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Body
Much of what makes haskell really nice to use in my opinion are combinators such as <code>(.)</code>, <code>flip</code>, <code>$</code> <code><*></code> and etc. It feels almost like I can create new syntax when I need to. Some time ago I was doing something where it would be tremendously convenient if I could "flip" a type constructor. Suppose I have some type constructor: <pre><code>m :: * -> * -> * </code></pre> and that I have a class <code>MyClass</code> that needs a type with a type constructor with kind <code>* -> *</code>. Naturally I would choose to code the type in such a way that I can do: <pre><code>instance MyClass (m a) </code></pre> But suppose I can't change that code, and suppose that what really fits into <code>MyClass</code> is something like <pre><code>type w b = m b a instance MyClass w where ... </code></pre> and then I'd have to activate <code>XTypeSynonymInstances</code>. Is there some way to create a "type level combinator" <code>Flip</code> such that I can just do: <pre><code>instance MyClass (Flip m a) where ... </code></pre> ?? Or other type level generalisations of common operators we use in haskell? Is this even useful or am I just rambling? Edit: I could do something like: <pre><code>newtype Flip m a b = Flip (m b a) newtype Dot m w a = Dot m (w a) ... </code></pre> But then I'd have to use the data constructors <code>Flip</code>, <code>Dot</code>, ... around for pattern matching and etc. Is it worth it?
Tags
<haskell><types><combinators><type-level-computation>
Title
Are there "type-level combinators"? Will they exist in some future?
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1. USRafael S. Calsaverini
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1. USRafael S. Calsaverini
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