On 10 Aug 2006 15:04:19 +0200, Martin Rubey <[EMAIL PROTECTED]> wrote:
Dear Igor,
"Igor Khavkine" <[EMAIL PROTECTED]> writes:
> -> symr := g(b, (a | notOrdered?(a,b)) == g(b,a)
there are some typos hidden in the line above. The operation "rule" is missing,
"notOrdered?" is undefined, and you seem to be replacing g(b, a) by g(a, b)...
Right, sorry about that. Must have been hasty.
Still:
symr := rule g(b, (a | a < b)) == g(a, b)
does not seem to work. After some experimenting, it occurred to me that the
suchThat predicate "|" might refer only to a *single* variable. I.e., in
(a | a < b)
b seems to be taken to be a constant. Note however, that I did *not* verify
this claim!
That's what I suspected as well.
Still, this idea leads to a workaround, by using hyperdoc and browsing
RewriteRule. Try the following:
g := operator 'g
swap := rule g(b, a) == g(a, b)
symr := suchThat(swap, [a,b], l +-> (output l; l.1 < l.2))
Excellent! I've also noticed suchThat(), but apparently wasn't as good
at deciphering its documentation.
Unfortunately, the condition seems to be evaluated once too often. I have no
idea why:
(14) -> symr g(x,y)
[y,x]
[y,x]
(14) g(x,y)
(15) -> symr g(y,x)
[x,y]
[y,x]
[y,x]
(15) g(x,y)
Even if the rule gets evaluated a few more times than necessary the
example you provided seems to work. Thanks a lot!
Maybe Axiom tries to apply a rule until the result doesn't change anymore...
That would explain infinite loops in simple minded rules like the
first one I thought of.
Igor
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