ztellman/riddley

Walker is my name
and I am the same.
Riddley Walker.
Walking my riddels
where ever theyve took me
and walking them now
on this paper the same.

from Riddley Walker by Russell Hoban

Code may be data, but only some of that data is executable. If we want to perform a pervasive code transformation, using something like clojure.walk presents a few problems:

• binding forms are treated the same as actual expressions
• clojure.walk/macroexpand-all will pass in a nil &env to all macros
• macroexpansion doesn't expand inlined functions

This means that transforms that we intend to apply to expressions may have unintended consequences on a fn, let, or case form. It also means that any macro which relies on &env will not compose with our transformation. Finally, if inlined functions aren't expanded, certain transformations will break.

[riddley "0.2.0"]

Riddley provides a correct riddley.walk/macroexpand-all, which preserves the binding information in &env and expands inlined functions, and riddley.walk/walk-exprs, which is a general mechanism for code walking and transformation.

walk-exprs takes two arguments, a predicate for whether it should transform the sub-form, and a handler for doing the transformation.

riddley.walk> (walk-exprs number? inc '(let [n 1] (+ n 1)))
(let* [n 2] (. clojure.lang.Numbers (add n 2)))

Notice that walk-exprs implicitly macroexpands the form, including the inline form for +. Unlike clojure.walk, if handler is called, sub-forms will not be walked. The handler function is responsible for recursively calling walk-exprs on the form it's handed.

Access to &env is available via (riddley.compiler/locals) if you need it as part of your transformation.

Full documentation can be found here.

Copyright © 2013 Zachary Tellman

Distributed under the MIT License.