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(unmemoize_delay): Extend the environment before

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unmemoizing the promise thunk.  This fixes a segmentation fault
reported by Frank Schwidom.
This commit is contained in:
Neil Jerram 2007-10-21 20:43:14 +00:00
parent 4098fda1e6
commit acbfb5946b
2 changed files with 13 additions and 1 deletions
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8
libguile/eval.c
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@ -1268,7 +1268,13 @@ static SCM
unmemoize_delay (const SCM expr, const SCM env)
{
const SCM thunk_expr = SCM_CADDR (expr);
return scm_list_2 (scm_sym_delay, unmemoize_expression (thunk_expr, env));
/* A promise is implemented as a closure, and when applying a
closure the evaluator adds a new frame to the environment - even
though, in the case of a promise, the added frame is always
empty. We need to extend the environment here in the same way,
so that any ILOCs in thunk_expr can be unmemoized correctly. */
const SCM new_env = SCM_EXTEND_ENV (SCM_EOL, SCM_EOL, env);
return scm_list_2 (scm_sym_delay, unmemoize_expression (thunk_expr, new_env));
}