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* Simulate conventional laziness a bit better still by "allocating"

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all local variables when entering a new scope.  I.e., don't do
  implicit let-floating.
This commit is contained in:
Eelco Dolstra 2007-10-11 22:42:09 +00:00
parent 981afe821c
commit 74ce938e18
4 changed files with 49 additions and 5 deletions
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42
src/libexpr/nixexpr.cc
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@ -201,6 +201,48 @@ Expr substitute(const Substitution & subs, Expr e)
}
Expr allocCells(Expr e)
{
checkInterrupt();
ATerm e2;
if (matchClosed(e, e2)) return e;
int i;
if (matchCell(e, i, e2))
return allocCell(allocCells(e2));
if (ATgetType(e) == AT_APPL) {
AFun fun = ATgetAFun(e);
int arity = ATgetArity(fun);
ATerm args[arity];
bool changed = false;
for (int i = 0; i < arity; ++i) {
ATerm arg = ATgetArgument(e, i);
args[i] = allocCells(arg);
if (args[i] != arg) changed = true;
}
return changed ? (ATerm) ATmakeApplArray(fun, args) : e;
}
if (ATgetType(e) == AT_LIST) {
unsigned int len = ATgetLength((ATermList) e);
ATerm es[len];
ATermIterator i((ATermList) e);
for (unsigned int j = 0; i; ++i, ++j)
es[j] = allocCells(*i);
ATermList out = ATempty;
for (unsigned int j = len; j; --j)
out = ATinsert(out, es[j - 1]);
return (ATerm) out;
}
return e;
}
/* We use memoisation to prevent exponential complexity on heavily
shared ATerms (remember, an ATerm is a graph, not a tree!). Note
that using an STL set is fine here wrt to ATerm garbage collection