210856dd57
* start of generic classes * fix regressions * class functions in interfaces * access to class function on interface from class parameter * more stuff working for generic classes * fixing bugs * update TypeEqual for generic classes * fixing bugs and finding new ones * disable unqualified access to members from other members for now * minor edits * bug fixes * introduce compile_time_value to use in type checker instead of constant_value * cleanup * put a CHECK back in * failure test cases for the new FATAL_COMPILATION_ERROR * change a runtime FATAL into a FATAL_COMPILATION_ERROR * Update executable_semantics/ast/declaration.h Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/action_stack.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/interpreter.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/interpreter.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/resolve_names.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * responses to reviews * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * rename compile_time_value to symbolic_identity * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/type_checker.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * Update executable_semantics/interpreter/value.cpp Co-authored-by: Jon Meow <jperkins@google.com> * more edits from review * Apply suggestions from code review Co-authored-by: Geoff Romer <gromer@google.com> * review responses * Update executable_semantics/interpreter/interpreter.cpp Co-authored-by: Geoff Romer <gromer@google.com> * const impl_scope for TypeCheckChoiceDeclaration * add some const Co-authored-by: Jon Meow <jperkins@google.com> Co-authored-by: Geoff Romer <gromer@google.com>
The code in this directory defines the AST that represents Carbon code in the
rest of executable-semantics.
The AST is not quite immutable, because some node properties are set during some
phase of static analysis, rather than during parsing. However, AST mutations are
monotonic: once set, a node property cannot be changed. Furthermore, if a
property is set after parsing, its documentation specifies what phase is
responsible for setting it. Certain properties have has_foo() members for
querying whether they are set, but those are for internal use within the phase
that sets them. As a result, you can think of the AST as if it were immutable,
but with certain parts that you can't yet observe, depending on what phase of
compilation you're in.
All node types in the AST are derived from AstNode, and use
LLVM-style RTTI to support
safe down-casting and similar operations. Each abstract class Foo in the
hierarchy has a kind method which returns a enum FooKind that identifies the
concrete type of the object, and a FooKind value can be safely static_casted
to BarKind if that value represents a type that's derived from both Foo and
Bar.
We rely on code generation to help enforce those invariants, so every node type
must be described in ast_rtti.txt. See the documentation in
(gen_rtti.py)[../gen_rtti.py], the code generation script, for details about
the file format and generated code.
The AST class hierarchy is structured in a fairly unsurprising way, with
abstract classes such as Statement and Expression, and concrete classes
representing individual syntactic constructs, such as If for if-statements.
Sometimes it is useful to work with a subset of node types that "cuts across"
the primary class hierarchy. Rather than deal with the pitfalls of multiple
inheritance, we handle these cases using a form of type erasure: we specify a
notional interface that those types conform to, and then define a "view" class
that behaves like a pointer to an instance of that interface. Types declare that
they model an interface Foo by defining a public static member named
ImplementsCarbonFoo. See ValueNodeView for an example of
this pattern.