[Haskell-cafe] Who generates Haskell code and uses type information at runtime?

Martin Hofmann martin.hofmann at uni-bamberg.de
Wed Mar 18 06:31:00 EDT 2009

> GHC is the current state of the art, which will give you a full
> Haskell AST enriched with type information. You can then just modify the 
> AST directly.

I experimented with the AST from HscTypes.CoreModule in the ghc api.
However, it seems that this representation is too far away from my
theory. I would prefer something similar as Template Haskell.

> The ghc-api is somewhat sparsely documented

That might be the reason, why I have not seen how it can help me.

> It really depends on what you are trying to do...

Putting in a nutshell, I generalize an extensional defined function
definition into a recursive one. This is done in a number of steps by
modifying expressions and exploiting type information of
sub-expressions. For example: 

rev [] = []
rev [a] = [a]
rev [a,b] = [b,a]
rev [a,b,c] = [c,b,a]


rev x = y


rev [] = []
rev (x:xs) = (y:ys)


rev [] = []
rev (x:xs) = (last (x:xs)) : (reverse (x:xs))

The initial set of rules is given by the user (in a file, via IO, ...).
The problem later is to infer the type of an intermediate variable, e.g.



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