Walker is my name
and I am the same.
Walking my riddels
where ever theyve took me
and walking them now
on this paper the same.
from [Riddley Walker](http://en.wikipedia.org/wiki/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 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](http://aleph.io/codox/riddley/).
Copyright © 2013 Zachary Tellman
Distributed under the MIT License.