Fix 2011-11-17 regression.

This addresses a regression caused by commit
68ca87bc780e25dea1418019161d99727225d1ce, affecting a hundred
releases of TXR from 42 to 141.

The copy_alist call to deeply clone the variable bindings was
carelessly replaced with copy_list, to address the problem
that functions weren't able to mutate outer bindings.

However, the parameter binding code depends on the deep
cloning; it destructively manipulates bindings with the
understanding that they are copies that will be thrown away.

Test case:

@(define f0 (var))
@(end)
@(define f1 (out1 out2 var))
@  (bind out1 `a:@var`)
@  (maybe)
@    (f0 `b:@var`)
@  (end)
@  (bind out2 `a:@var`)
@(end)
@(f1 o1 o2 "z")

This program incorrectly binds o1 and o2 to different
strings, "a:z" and "a:b:z" respectively, because
the f0 pattern function call has the unwanted effect of
mutating var. Expected behavior is that both o1 and
o2 are bound to identical strings, "a:z" and "a:z".

* match.c (h_fun, v_fun): When binding arguments, extend
the environment with new bindings instead of trying to
re-use existing ones, because we do not have a copy of the
binding cells, like we used to when bindings_cp was
produced by a copy_alist call.

0 files changed, 0 insertions, 0 deletions