matcher: fix null value ambiguity in hash match.

Hash pattern matching must not assume that if gethash returns
nil, the item is not found. That's just a convenience that can
be coded in some situations, not in a general mechanism.

* share/txr/stdlib/match.tl (compile-hash-match): Allocate a
gensym that serves as a unique object. Pass this to gethash
as the alt argument, and then check whether gethash has
returned this value to indicate failure.

0 files changed, 0 insertions, 0 deletions