Would you have been happier if match-define had been named define-match, the
way it should have been done if we had insisted on consistency in coding
guidelines?
Your cond would have looked like this:
(cond ...
[(condition? z-sig)
(define x (compute-x z))
(define-match (foo y-bar y-baz) ...)
(define-values (a b) ...)
(define (f x y z w) 0)
(the-computation x y-baz a b)]
...)
On Nov 12, 2010, at 6:40 PM, Neil Toronto wrote:
> In internal definition contexts, I've been using the following macro to
> define everything but functions:
>
> (define-syntax (def stx)
> (syntax-case stx (values)
> [(_ x e0 e ...)
> (identifier? #'x)
> (syntax/loc stx
> (define x (let () e0 e ...)))]
> [(_ (values x ...) e0 e ...)
> (andmap identifier? (syntax->list #'(x ...)))
> (syntax/loc stx
> (define-values (x ...) (let () e0 e ...)))]
> [(_ (values pat ...) e0 e ...)
> (syntax/loc stx
> (match-define (list pat ...)
> (call-with-values (lambda () e0 e ...) list)))]
> [(_ pat e0 e ...)
> (syntax/loc stx
> (match-define pat (let () e0 e ...)))]))
>
>
> So these do the obvious things:
>
> (def a 4)
> (def (values) (values))
> (def (values b c) (values 4 5))
> (def (values (list d e) f)
> (values (list 4 5) 6))
>
> Common cases like (def x:id e ...+) and (def (values x:id ...) e ...+) expand
> to the most direct define-like form. (It avoids `match-define' because
> `match-define' 1) always binds a failure thunk; and 2) forces multiple values
> to be converted to lists.)
>
> With `def', it's easier to recognize a sequence of definitions leading up to
> a computation buried inside a conditional branch. For example, instead of:
>
> (cond ...
> [(the-condition? z-sig)
> (define x (compute-x z))
> (match-define (foo y-bar y-baz) y)
> (define-values (a b) (get-some-values x y-bar))
> (the-computation x y-baz a b)] ...)
>
> I have:
>
> (cond ...
> [(the-condition? z-sig)
> (def x (compute-x z))
> (def (foo y-bar y-baz) y)
> (def (values a b) (get-some-values x y-bar))
> (the-computation x y-baz a b)] ...)
>
> It's hard to miss all the `def's lined up in the same column.
>
> Have I left anything out? Does anybody else think it's awesome/useful?
> Hideous?
>
> Neil T
>
> (It's a shame it can't do functions, but there's no way to tell whether (def
> (foo y-bar y-baz) ...) is intended to match a foo struct or define a foo
> function. Also, optional parameters and struct matching look the same. I
> wrote a `defun' macro that solves the latter problem - it even does currying
> and keywords - but I can't say that I like it yet.)
>
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