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Add functors (callable attribute sets).

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With this, attribute sets with a `__functor` attribute can be applied
just like normal functions. This can be used to attach arbitrary
metadata to a function without callers needing to treat it specially.
This commit is contained in:
Shea Levy 2014-10-15 22:04:48 -04:00
parent 8cfe939b0f
commit 997defa166
4 changed files with 15 additions and 1 deletions
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12
src/libexpr/eval.cc
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@ -180,6 +180,7 @@ EvalState::EvalState(const Strings & _searchPath)
, sFile(symbols.create("file"))
, sLine(symbols.create("line"))
, sColumn(symbols.create("column"))
, sFunctor(symbols.create("__functor"))
, repair(false)
, baseEnv(allocEnv(128))
, staticBaseEnv(false, 0)
@ -885,6 +886,17 @@ void EvalState::callFunction(Value & fun, Value & arg, Value & v, const Pos & po
return;
}
if (fun.type == tAttrs) {
auto found = fun.attrs->find(sFunctor);
if (found != fun.attrs->end()) {
forceValue(*found->value);
Value * v2 = allocValue();
callFunction(*found->value, fun, *v2, pos);
forceValue(*v2);
return callFunction(*v2, arg, v, pos);
}
}
if (fun.type != tLambda)
throwTypeError("attempt to call something which is not a function but %1%, at %2%", fun, pos);