heh! well everyone was busy working on icfp or something, so the newsgroup was pretty dead :-) And I played with opengl a little, which gave better results than I thought, but not good enough to pursue, and the whole program was in imperative "do"s anyway, so I couldnt quite see what was the point of moving to a non-imperative language!
End of rant...
It looks like there's a huge amount of documentation on the parsing process, but it's kindof more fun to just figure it out ourselves, I think?
Anyway, for handling loops, what I'm thinking is maybe the Map that holds variables, rather than holding a "Double" type should hold a "variant" type, something like:
data Variant = VDouble Double | VString String | ... etc...
then, to handle loops, which basically involves creating a "pointer" variable, we simply add a variant type that holds a program:
data Variant = ... | VProgram Program
... and then we can just assign to the Variant type in the map corresponding to the symbol the rest of the program that follows that symbol.
Note that we have to reverse the Program data type to get this to work effectively:
data Program = ProgramLeaf Statement | ProgramTree Statement Program
deriving(Show)
... errr... I think... because that way we can grab any part of the program tree and store that as a Variant in the map.
How does that sound? That ought to get looping working? Then we just have to handle conditionals, which I havent thought at all about yet.