Boilerplate-free annotation of ASTs in Haskell?

Question

I\'ve been fiddling around with the Elm compiler, which is written in Haskell.

I\'d like to start implementing some optimizations for it, and part of this involves t

Answer 1

This question is very similar to a past one talking about the particular annotation of source location. The solution I find most elegant is to re-define Expr and Def to provide a constructor that contains an annotation:

data Expr = PlusExpr Expr Expr
          | AnnotatedExpr Annotation Expr
          ...