suzanne.soy/fear-of-macros
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Merge branch 'master' into gh-pages

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Greg Hendershott 2012-11-02 11:44:54 -04:00
commit c41afe8d42
2 changed files with 25 additions and 21 deletions
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main.rkt
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@ -496,21 +496,27 @@ We can write:
(match (syntax->list stx)
[(list name condition true-expr false-expr)
(datum->syntax stx `(cond [,condition ,true-expr]
[else ,false-expr]))]))
[else ,false-expr]))]))]
Great. Now let's try using it:
@i[
(our-if-using-match #t "true" "false")
]
But wait, we can't. It's complaining that @racket[match] isn't
defined. We haven't required the @racket[racket/match] module?
Oops. It's complaining that @racket[match] isn't defined.
It turns out we haven't. Remember, this transformer function is
working at compile time, not run time. And at compile time, only
@racket[racket/base] is required for you automatically. If we want
something like @racket[racket/match], we have to require it
ourselves---and require it @italic{for compile time}. Instead of using
plain @racket[(require racket/match)], the way to say this is to use
@racket[(require (for-syntax racket/match))]---the @racket[for-syntax]
part meaning, "for compile time".
Our transformer function is working at compile time, not run time. And
at compile time, only @racket[racket/base] is required for you
automatically---not the full @racket[racket].
Anything beyond @racket[racket/base], we have to require
ourselves---and require it for compile time using the
@racket[for-syntax] form of @racket[require].
In this case, instead of using plain @racket[(require racket/match)],
we want @racket[(require (for-syntax racket/match))]---the
@racket[for-syntax] part meaning, "for compile time".
So let's try that: