Hello,
Data.Typeable gives you most of what you want except for access to
function bodies.
-Jeff
On Tue, Mar 11, 2008 at 6:17 AM, Martin Hofmann
I am trying to port a programme written in Maude, which is a reflective language based on rewriting logic ( http://maude.cs.uiuc.edu/ ), to Haskell. I thought using Template Haskell might be a good idea, but I got stuck and now I am wondering if this is really possible in Haskell. Let me give an example of a Maude module defining the function last over a list of Peano numbers.
fmod LAST is sorts Peano PeanoList .
op 0 : -> Peano [ctor] . op s : Peano -> Peano [ctor] .
op [] : -> PeanoList [ctor] . op cons : Peano PeanoList -> PeanoList [ctor] .
op last : PeanoList -> Peano .
vars X Y : Peano . var Xs : PeanoList .
eq last(cons(X,[])) = X . eq last(cons(X,cons(Y,Xs))) = last(cons(Y,Xs)) .
endfm
So, last(cons(s(0),cons(s(s(0)),cons(s(s(s(0))),[])))) would reduce to s(s(s(0))). The cool thing about Maude is, that terms, modules, ... can be lifted to the meta level. For example:
upModule('LAST, false)
would yield
fmod 'LAST is including 'BOOL . sorts 'Peano ; 'PeanoList . none op '0 : nil -> 'Peano [ctor] . op '`[`] : nil -> 'PeanoList [ctor] . op 'cons : 'Peano 'PeanoList -> 'PeanoList [ctor] . op 'last : 'PeanoList -> 'Peano [none] . op 's : 'Peano -> 'Peano [ctor] . none eq 'last['cons['X:Peano,'`[`].PeanoList]] = 'X:Peano [none] . eq 'last['cons['X:Peano,'cons['Y:Peano,'Xs:PeanoList]]] = last['cons[ 'Y:Peano,'Xs:PeanoList]] [none] . endfm
I also have access, e.g. to the defined type constructors.
So upOpDecls('LAST,false).
yields
op '0 : nil -> 'Peano [ctor] . op '`[`] : nil -> 'PeanoList [ctor] . op 'cons : 'Peano 'PeanoList -> 'PeanoList [ctor] . op 'last : 'PeanoList -> 'Peano [none] . op 's : 'Peano -> 'Peano [ctor] .
Given an arbitrary function, I have access to its definition, its types and the type constructors, all as ADTs.
Is this possible with Template Haskell, or in some other way?
Thanks a lot,
Martin
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