Hello, I think what I'm trying to do is too ambitious, but I thought I would ask to see if it is possible. It seems like there is no easy way to do it, given what I've seen of the GHC API. I would like to have a function, say it is called "this", which has the following effect in ghci
let n = 2 in this n 2
In other words, it captures all the variables which are in scope, and adds them to the GHCi environment. Somebody helpful will probably say "But you can just write 'let n = 2'!", but that is not the aim. There are several aims. One is to be able to look at the variables inside a function which one is trying to debug, then inserting 'this' will cause them to be in scope, I think that would be useful. A more important aim is to be able to use existentially quantified variables easily. Currently I can do:
reifyIntegral 5 (\n -> print $ reflectNum n) 5
but how can I get GHCi to have an 'n' binding which is inside the function? Clearly just returning 'n' will not work:
reifyIntegral 5 id
<interactive>:1:0: Inferred type is less polymorphic than expected ... This is what I am thinking of doing, but as I said it seems ambitious. There are several easier things one could think of:
let n = 2 in bind "n" n n 2
If it were possible to add bindings to the GHCi bindings list, then this would be easy. Is it possible? The documentation doesn't seem to mention such a capability. Also, probably another useful feature would be to combine 'this' with something in the IO monad:
withProgName "blah" thisIO getProgName "blah"
So, are these things currently possible? Planned? Have the functions I describe been implemented already? I think there is a GHCi debugger in the works, so maybe functionality like this will be part of it, I didn't want to start something on my own if that is the case... Many thanks, Frederik -- http://ofb.net/~frederik/