Re: [Haskell-cafe] Displaying infered type signature of 'offside' functions

kahl@cas.mcmaster.ca wrote:

Jules Bean wrote, concerning the problem of getting at the types of local definitions:

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Simon Peyton-Jones wrote: The principal difficulties here are to do with "what do we want" rather the implementation challenges.

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1. Should the compiler print the type of every declaration? Should GHCi allow you to ask the type of a local decl?

IMO, ghci should definitely allow you to ask. This comes up for me every time that I write any haskell code (and in general I end up hoisting local definitions to the top level, which is a real pain if there is local scope, data or type, to hoist with it).

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2. How should the variables be identified? There may be many local bindings for 'f', so you can't say just ":t f". Ditto if dumping all local bindings.

I think this is a hard question. I was imagining some kind of hierarchical system like foo.f, in the case that f is locally defined inside foo. (Yes I know we can't easily use '.' for that). There might be might be multiple fs inside the definition of foo; indeed there might even be multiple fs nested inside each other.

I just wanted to contribute a PRACTICAL TRICK I use:

* If the local definition is a pattern binding

f = ...

then I just add

f :: Ordering

* If the local definition is a, say binary, function binding

f p1 p2 = ...

then I just add

f :: Float -> Double -> Ordering

(Type does not matter for the number of function arrows you need to put; only the syntactic arity of the bindings matters here.)

This relies on the fact that the types Float, Double, and Ordering very rarely occur in my code --- pick your own.

Why not just declare a type you don't use?