This is what hint does, isn't it? However, this still leaves it to me to infer what type [|a|] in [| reverse (a:b:[]) = (b:a:[]) |] is. Thanks a lot anyway. Martin On Thu, 2009-03-12 at 12:59 -0200, Daniel Gorín wrote:

would using ghc-as-a-library to type (strings with) haskell expressions at runtime help?

On Mar 12, 2009, at 12:37 PM, Martin Hofmann wrote:

...

I am doing meta-programming at runtime. So my program gets a full Haskell declaration in expression quotation ([d|...|]) modifies it and returns the modified expression. Therefore, I need type information of this expression, and any subexpression, at _runtime_ ! For example:

[d| reverse x1 = y1 |]

- rewrites_to ->

[d| reverse x2:xs = y2:ys |]

- rewrites_to ->

[d| reverse x:xs = reverse xs ++ [x] |]

reverse :: [a] -> [a] implies x2,y2 :: a x1,y1,xs,ys :: [a]

TH.reify is not applicable, because I need the information at runtime and I am in IO. I suppose Data.Dynamic does not work either, because [| xs|] :: ExpQ and not [a].

So it looks like I need my own type checker and inference and tag each subexpression with its type. If so, I can even omit TH and use my own data type for the abstract syntax tree. This annoys me a bit, because for me it seems that all I need is already there.

Did anybody have similar problems, because I shouldn't be the only one doing dynamic typing in a static language? Is there a Haskell implementation of the paper "Typing Dynamic Typing" by Baars and Swierstra (http://people.cs.uu.nl/arthurb/dynamic.html ), so I can try out if this helps me?

Any help, comments, and how-to-suggestions are highly welcome.

Thanks a lot,

Martin

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