An introduction to deep code-walking macros with Clojure (2013)

by foguson 6/21/2022, 8:20:11 PM with 2 comments
  • by cedon 6/23/2022, 4:07:51 AM

    As an aside, Julia's MacroTools.jl defines pre- and post- code walking in four lines:

        walk(x, inner, outer) = outer(x)
    walk(x::Expr, inner, outer) = outer(Expr(x.head, map(inner, x.args)...))

    postwalk(f, x) = walk(x, x -> postwalk(f, x), f)
    prewalk(f, x)  = walk(f(x), x -> prewalk(f, x), identity)
    It's dead simple and obvious in retrospect, but I don't think I would have ever thought of that! I've always wondered if there's a lineage to this set of definitions. Does anyone know?

  • by thomon 6/23/2022, 8:26:08 AM

    I love this sort of thing, but I often get the sense from Clojurists I’ve worked with that macros are seen as too complicated (even slightly naughty) for most codebases. Always seems a shame as it’s the main superpower you’re getting from Lisp.