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122 lines
2.8 KiB
C++
122 lines
2.8 KiB
C++
// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
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#pragma once
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#include "Luau/Variant.h"
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#include <string>
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namespace Luau
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{
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/**
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* The 'level' of a TypeVar is an indirect way to talk about the scope that it 'belongs' too.
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* To start, read http://okmij.org/ftp/ML/generalization.html
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*
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* We extend the idea by adding a "sub-level" which helps us to differentiate sibling scopes
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* within a single larger scope.
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*
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* We need this because we try to prototype functions and add them to the type environment before
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* we check the function bodies. This allows us to properly typecheck many scenarios where there
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* is no single good order in which to typecheck a program.
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*/
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struct TypeLevel
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{
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int level = 0;
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int subLevel = 0;
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// Returns true if the typelevel "this" is "bigger" than rhs
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bool subsumes(const TypeLevel& rhs) const
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{
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if (level < rhs.level)
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return true;
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if (level > rhs.level)
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return false;
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if (subLevel == rhs.subLevel)
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return true; // if level == rhs.level and subLevel == rhs.subLevel, then they are the exact same TypeLevel
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// Sibling TypeLevels (that is, TypeLevels that share a level but have a different subLevel) are not considered to subsume one another
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return false;
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}
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TypeLevel incr() const
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{
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TypeLevel result;
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result.level = level + 1;
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result.subLevel = 0;
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return result;
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}
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};
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inline TypeLevel min(const TypeLevel& a, const TypeLevel& b)
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{
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if (a.subsumes(b))
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return a;
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else
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return b;
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}
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namespace Unifiable
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{
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using Name = std::string;
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struct Free
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{
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explicit Free(TypeLevel level);
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int index;
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TypeLevel level;
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// True if this free type variable is part of a mutually
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// recursive type alias whose definitions haven't been
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// resolved yet.
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bool forwardedTypeAlias = false;
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private:
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static int nextIndex;
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};
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template<typename Id>
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struct Bound
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{
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explicit Bound(Id boundTo)
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: boundTo(boundTo)
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{
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}
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Id boundTo;
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};
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struct Generic
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{
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// By default, generics are global, with a synthetic name
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Generic();
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explicit Generic(TypeLevel level);
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explicit Generic(const Name& name);
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Generic(TypeLevel level, const Name& name);
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int index;
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TypeLevel level;
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Name name;
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bool explicitName;
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private:
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static int nextIndex;
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};
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struct Error
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{
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// This constructor has to be public, since it's used in TypeVar and TypePack,
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// but shouldn't be called directly. Please use errorRecoveryType() instead.
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Error();
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int index;
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private:
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static int nextIndex;
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};
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template<typename Id, typename... Value>
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using Variant = Variant<Free, Bound<Id>, Generic, Error, Value...>;
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} // namespace Unifiable
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} // namespace Luau
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