Write DSL for quickly building C ASTs

[patrickt]

e.g.

cmain = function "main" int_t $ block $ do
   call "printf" [str "hello world"]
   decl int_t "x" (Just (int 0))
   ret "x"

[patrickt]

This is mostly done, just have to finish Language.Bracer.Backends.C.Scribe.