Hygme

Overview

Hygme implements a simple interpreter with hygienic macro expansion, as described by Kohlbecker.

Syntax

Hygme uses s-expressions, but has the following BNF-ish:

Abs := (fn var body)
Var := <symbol>
Const := <string> | <symbol> | <number> | <boolean> ...
Cond := (if <condition> <consequent> <alternate>)
Assm := (set! var value)
App := (<expr> <expr> ...)

Abs (abstractions), you'll notice take, and must have a single argument. Multiple arguments can be obtained via currying, though zeroadic functions simply are not supported.

Where applicable, the host scheme reader is deferred too, which means that is either #f or #t.

Initial environment

Procedures: cons, car, cdr, list, not, +, -, *, /

Macros: unless, let, or, and

Expansion

unless expands as follows:

hygme> (hygme-expand '(unless foo bar))
=> (if (not foo) bar)

let expands as follows:

hygme> (hygme-expand '(let foo bar (cons foo '())))
=> ((fn foo2835 (cons foo2835 (quote ()))) bar)

and expands as follows:

hygme> (hygme-expand '(and foo bar))
=> (if foo bar #f)

or expands as follows:

hygme> (hygme-expand '(or foo bar))
=> ((fn v2995 (if v2995 v2995 bar)) foo)

Copyright

References

[Kohlbecker]: http://www.cs.ucdavis.edu/~devanbu/teaching/260/kohlbecker.pdf Kohlbecker, E.; Friedman, D. P.; Felleisen, M.; Duba, B. (1986). "Hygienic Macro Expansion". ACM conference on LISP and functional programming.

apg/hygme