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Support arbitrary expression as argument to
interval(...) and `inte…
…rval_ns(...)`. So far we used constructor expressions like `interval(...)` to create *constants* of the given type, and for that we required that the argument was a single atomic value. The result was that these constructor expressions were really more like literals for the corresponding types than "normal" expressions. While that's useful internally, it's confusing for the user. This commits is beginning to change that, using `interval`/`interval_NS` as the first instances that now supports arbitrary expressions as its argument. In follow-up commits, we'll port other constructor expressions over to that new syntax. (This also unifies HILTI & Spicy to each provide both of those interval constructors.) To make this change without loosing a way to create actual constants (which we need at some places), we implement this in two stages: the parser initially turns such `interval(...)` expressions into call operators[1] that the types now define for each desired constructor. We then extend the normalizer to look at all the relevant call operators: if they are just receiving a constant value as their argument, then it substitutes them with a plain ``Ctor`` node (``ctor::Interval`` in our cases here). That check for "if they just receive a constant value" isn't quite trivial in general. In our case, where we just want to go back to what we had, it's not that difficult, but more generally it would be nice if we had a constant folder that could compute results even for more complex, but constant, expressions. As that's a piece that our AST infrastructure is still missing, this commit starts going that route by adding a new "constant folder" visitor. Right now, it's covers only the simple cases we need here, but it's something we can extend going forward. Addresses #1123. [1] These call operators are a bit special because they actually don't have anything to call: in `interval(42)` the `interval` isn't any kind of actual value; we just need it for overload resolution. To make that work, we use a `expression::Member` as the first operand, which models a predefined ID. Normally `Member` is just for field lookups in, e.g., structs, but it works just as well elsewhere.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,48 @@ | ||
| // Copyright (c) 2020-2021 by the Zeek Project. See LICENSE for details. | ||
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| #include <hilti/ast/ctors/integer.h> | ||
| #include <hilti/ast/detail/visitor.h> | ||
| #include <hilti/ast/expression.h> | ||
| #include <hilti/ast/operators/signed-integer.h> | ||
| #include <hilti/ast/operators/real.h> | ||
| #include <hilti/ast/types/integer.h> | ||
| #include <hilti/base/logger.h> | ||
| #include <hilti/base/util.h> | ||
| #include <hilti/ast/builder/expression.h> | ||
| #include <hilti/compiler/detail/visitors.h> | ||
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| using namespace hilti; | ||
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| namespace { | ||
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| // For now, this is only a very basic constant folder that only covers cases we | ||
| // need to turn type constructor expressions coming with a single argument into | ||
| // ctor expressions. | ||
| struct VisitorConstantFolder : public visitor::PreOrder<Ctor, VisitorConstantFolder> { | ||
| result_t operator()(const expression::Ctor& n, position_t p) { return n.ctor(); } | ||
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| result_t operator()(const operator_::signed_integer::SignNeg& n, position_t p) { | ||
| if ( auto op = detail::foldConstant<ctor::SignedInteger>(n.op1()) ) | ||
| return ctor::SignedInteger(- op->value(), op->width(), op->meta()); | ||
| else | ||
| return {}; | ||
| } | ||
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| result_t operator()(const operator_::real::SignNeg& n, position_t p) { | ||
| if ( auto op = detail::foldConstant<ctor::Real>(n.op1()) ) | ||
| return ctor::Real(- op->value(), op->meta()); | ||
| else | ||
| return {}; | ||
| } | ||
| }; | ||
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| } // anonymous namespace | ||
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| Result<Ctor> detail::foldConstant(const Expression& expr) { | ||
| auto v = VisitorConstantFolder(); | ||
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| if ( auto ctor = v.dispatch(expr) ) | ||
| return *ctor; | ||
| else | ||
| return result::Error("not a foldable constant expression"); | ||
| } |
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