I'm trying to give the user the possibility to jump to the definition of a
symbol in the source file. You click on the name of a function and you're send
to the module where it's defined. So I have an AST, and somewhere down the line
I have an Id object representing that function call. Then I just use ppr
alwaysQualify id to get the fully qualified name of the function, and I can
then use the module name to retrieve the source file etc.
No, no, don't do this. The ppr alwaysQualify thing tries hard to display the
thing *in the current scope*. So if you have
import M as N
it will, I think, print thing as N.f, N.g, etc, not as M.f, M.g. The intent is
to give user-comprehensible error messages.
What you want is to use
idName :: Id -> Name
nameModule_maybe :: Name -> Maybe Modlue
The latter gives you the *defining* module for the Id, which is what you
wanted. It returns nothing for local variables (e.g. lambda-bound).
This works well in cases, but not in others. It will sound silly to the gurus
on the list, but it's when the function has generics that it doesn't work. So a
function with a type class in its type signature will never be printed
qualified. It kinda like makes sense because I suppose some work has been done
so that it represents the function with proper types, etc., but how can I get
back to the original Id? How can I get back from that unqualified Id to the
qualified Id representing the function in the original module? I've been
looking round Name and OccName and all that but I'm not sure really what I'm
looking for.
Suppose we have List.sort :: Ord a => [a] -> [a]. And the program is
f x = sort [x,x]
Then, after type checking, the code looks more like this:
f :: Ord a => a -> [a]
f = /\a. \d:Ord a. let s :: [a] -> [a]
s = List.sort a d
in \(x:a). s [x,x]
Notice the local function 's'. (Well, its string-name is still "sort", but
it's not the global List.sort.) I think you are poking on 's'.
Happily, GHC 7 takes a simpler approach, and instead generate something more
like
f :: Ord a => a -> [a]
f = /\a. \d:Ord a.
\(x:a). List.sort a d [x,x]
So it may "just work" in GHC 7.
Hope this helps.
Good luck with EclipseFP. We need a good Haskell IDE.
Simon
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