On Tue, Oct 11, 2011 at 4:25 PM, Stephen Wrobleski <st...@localtoast.org>wrote:
> On Mon, Oct 10, 2011 at 09:24:09PM -0400, David Nolen wrote:
> > I'm not following. Getting accurate information about what failed to
> match
> > needs to be integrated. Given that match makes no restrictions on types
> > there's not much we can do except communicate where we were when the
> match
> > failed via an exception.
>
> Sorry, I was unclear. I was trying to say that having two versions,
> match-debug that throws exceptions, and match-normal that returns nil, is
> redundant - default behavior is easily set with an :else clause. Changing
> the behavior for something marked '-debug' seems like a bad idea as well.
>
> I personally think throwing exceptions is the Right Thing. When adding
> clauses incrementally, I'd rather get a direct error message for unexpected
> values. Exhaustive clauses are a good thing, and :else nil is a simple
> idiom for the 'other behavior'.
>
It's starting to look easier and less complex to stick with the current
behavior. I'll +1 this.
> > Ambrose had some arguments for keeping match and match-1 separate. At the
> > moment I don't see any real issues except that overloading match to
> handle
> > two different cases seems like we're making things slightly more complex.
>
> (Where are these arguments? I thought I remember a wiki with design notes,
> but can't seem to find it). I don't see how it's two different cases.
> Having match take a vector of expressions with 'pattern rows' seems like an
> unnecessarily visible optimization.
>
>
>
My concerns were we should tread carefully to avoid unexpected behavior.
Say we unify the behaviors of match-1 and match.
(match "asdf" ;; <- looks like a "match-1"
"no" 1
"asdf" 2)
(match ["asdf"] ;; <- looks like a "match"
["no"] 1
["asdf"] 2)
The second example _looks_ like it's matching a _vector_, but it's actually
matching
a pattern row. There is an important difference when using guards, for
example.
(match ["asdf"]
(["asdf"] :when (fn [a] ..)) 1) ;; <- illegal, cannot wrap
pattern row in list
If we can resolve this, it would be great!
Thanks,
Ambrose
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