Re: Inconsistent behaviour of the pattern matcher

[Mark H Weaver]

Stefan Israelsson Tampe <address@hidden> writes:

> On Sun, Apr 28, 2013 at 2:51 PM, Mark H Weaver <address@hidden> wrote:
>
>     Panicz Maciej Godek <address@hidden> writes:
>     
>     > (match #u8(1 2 3)
>     > (#u8(a b c)
>     > (list a b c)))
>     
>     This can't work because a uniform numeric vector cannot hold
>     symbols, so
>     #u8(a b c) cannot be represented in the source code.
>     
> please note a b c binds to values and is not symbols as in the pmatch
> matcher or match quasiquoute
> patterns. So with the right binder this could work.

Read what I wrote again: "#u8(a b c) cannot be represented in the
*source* code."  Remember that in Scheme (and Lisp), code is represented
as data.  So what datum do you expect 'read' to return after it consumes
"#u8(a b c)"?

We could extend (ice-9 match) to support uniform numeric vectors, but
the pattern syntax would have to be different.

>     If you want generic accessors, I guess the array accessors are
>     what you
>     want. Patches to extend the pattern matcher to handle arrays are
>     welcome :)
>
> Actually for ice-9 match we would like the upstream version to
> implement these concepts
> Try ask foof on irc #scheme if he accept a patch to implement this in
> a portable way or ask
> him if he thinks he could spend time on it!

Given that Guile's arrays are specific to Guile and not portable, I
doubt that foof would be interested in supporting them upstream.

> Only if we could accept a slow implementation of the matcher we can
> implement a general vector
> matcher by patching vector-ref etc.

Beyond the efficiency considerations, I'm not sure it's desirable for
the pattern #(a b c) to match #u8(1 2 3).

       Mark