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Simon Peyton Jones authored
"Short-cut" substitution means "do nothing if the substitution is empty". We *never* want do to that in the simplifier because even though the substitution is empty, the in-scope set has useful information: * We get up-to-date unfoldings; and that in turn may reduce the number of iterations of the simplifier * We avoid space leaks, because failing to substitute may hang on to old Ids from a previous iteration (This is what was causing the late inlining of foo in Trac #4428.)
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