Thomas Schilling wrote:
I bring this up because I have been working on a Scheme compiler in
Haskell for fun, and something like polymorphic variants would be quite
convinent to allow you to specify versions of the AST (input ast, after
closure conversion, after CPS transform, etc.), but allow you to write
functions that work generically over all the ASTs (getting the free
vars, pretty printing, etc.).
Proper subtyping or at least extendable ADTs would be nicer, but you
can have type-checked progress flags using phantom types, e.g.:
<snip>
I thought that phantom types might be a solution, but how to you
statically ensure that the AST has only the constructors that are
appropriate for each phase?
GADTS maybe. Constructors allowed in all phases, or in just one can be
encoded easily enough. But then how do you encode a constructor that can
be in two out of three phases? Maybe two phantom types? It all starts
getting a little hairy.
I will have to go through the papers that the others have provided to
see if someone has already explored this direction. I have an inkling
that there is a good idea here, it just might take some time to tease it
out.
Thanks for the replies.
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