isabella232 / riddley

code-walking without caveats

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

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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.

usage

[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.

license

Copyright © 2013 Zachary Tellman

Distributed under the MIT License.