This enables us to stop using `Env` in the typechecker. As a byproduct, this commit also restructures the interpreter to handle run-time global initialization as part of ordinary execution, using the Action stack.
- Rename `PointerValue` to `LValue` to reflect how it's actually used. We can introduce a `PointerValue` type when we add support for actual pointer values.
- Remove support for pattern assignment. It's unclear if Carbon will support this, and even if we do, it raises questions that should first be addressed in a language proposal, like "is the left-hand side of `(x, y) = (1, 2)` an lvalue, or a pattern, or both, or something else entirely?"
This lets us statically distinguish between code that works with arbitrary `Address`es and code that can only work with pointers to separately-allocated storage, and so we no longer need to worry about the latter code crashing at run-time (as `Heap::Deallocate` did) or silently doing the wrong thing (as `Heap::PrintAddress` did) if it's given the wrong kind of `Address`.
Arguably missed in #769
Note, this is reminding me we have more class members to rename for `_`, but I felt it's best to use the new naming instead of adding more to clean up.
This does a mass rename of:
- `SourceLoc()` -> `source_loc()` for property naming
- `loc` -> `source_loc_` for underscore+consistency
- Generally changing function args to `source_loc` for consistency
- `Tag()` -> `kind()` for property naming and `Kind` parity
- `tag` -> `kind_` for underscore
Also renames `Pos` and `Results` on `Action`. These are a bit of an exception in that most base classes only have `Tag` and maybe `SourceLoc`, whereas `Action` has a little more. I felt okay having `source_loc()` and `kind()` on the base class where children do `Exp()` and the like, but it felt weird to me to mix it on the same class.
The reason for doing this cross-class in one PR is so that I can do it efficiently with a global replace in the codebase, rather than e.g. changing `Expression` but having to read through compiler errors to determine where it's calling `Expression`'s `Tag` versus a different `Tag`. The end result should be equivalent.
The code is pretty intertwined: having the AST be truly mutable means (to me) changing parser.ypp to return non-const values, but then the way things are passed around between objects should be non-const (particularly an issue with lists), which then creates issues with construction of lists in the TypeChecker, which then TypeChecker needs to mostly be non-const.
Due to the difficulties in breaking this apart, whereas I'd previously considering refactoring accessor naming in the same PR, I've largely avoided doing so. The intent is then that this PR focuses mainly on const -> non-const AST behavior.
call_main moves out of interpreter.cpp so that interpreter.cpp can receive a fully const AST.
With this, only main.cpp instantiates an arena. Maybe we'll want to split that up more later (e.g., so that the runtime interpreter uses its own arena), but given the intent to have type-checking update the AST, I thought this was a reasonable approach for now in order to avoid ownership complexities.
Fixes#769
Along with #789 this addresses most of #769 although global_arena is still a TODO (that's widespread and overlaps with other changes so I wanted to do it after these are in).
Sorry about the big change, this is hard to split. ParenContents is used by both, templated, and expects the same pointer type. While I could duplicate ParenContents with some ExpressionParenContents or PatternParenContents, that seems a little kludgy versus a single large change handling both. The worst of it is that Expression is already pretty sweeping, Pattern is really just incrementally adding.
That said, I believe this includes a couple fixes I found with incorrect use of dyn_cast in typecheck.cpp (checked nullptr at the wrong step in 2 code locations). There's also a missing `*` in member.cpp this caught. I adjust passing of expressions for Return due to nullness (I felt adding another constructor was the best solution).
I add a `.Release()` to BisonWrap due to things like `$3.first` needing some way to work through BIsonWrap. I felt this was better than `operator->`, but feel free to comment if you prefer the other path (`.Release()` conveniently lets me do pair unwrapping, so it felt a better solution).
I do add a TODO to think about better Ptr-to-Ptr cast<> support too, though, as that doesn't work cleanly with LLVM's infra. But so far it seems to only come up in one spot, so I'm not prioritizing it.
This enables the interpreter logic to express its intent more directly, especially in the common cases, and enables us to get rid of ValAction. It's also a step toward simplifying and encapsulating `state->stack`.
This also eliminates the ctad wrapper for Stack: I think the leaning is to remove it. It felt worth keeping the constructor because constructing with a single element is a common use-case.
Adds a single-argument constructor for Scope because the `std::list<std::string>()` is common, and eliding it is consistent with what we've done for things like tuples.
I was considering a vector constructor due to the double-Push on line 1139, but thought the Push() semantics may mean that it's better not to provide.
`Pattern` is intended to pilot some changes I would like to apply to all our sum types:
- The alternatives are expressed as derived classes rather than members of a `std::variant`.
- The alternatives are classes in the [style guide sense](https://google.github.io/styleguide/cppguide.html#Structs_vs._Classes), meaning they can have invariants, but can't have public data members.
- Creating an object is expressed using a constructor rather than a factory function.
- Accessing an alternative is expressed as a cast (using LLVM's RTTI system) rather than `std::get` or a `Get` method.
Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>
- Switch code to llvm::raw_ostream as part of standardizing output forms.
- Preferring llvm::raw_ostream over std::ostream because other tooling code should be expected to rely on llvm more closely, and an overall preference towards library consistency.
- There are a couple spots in syntax/ that still use std streams, but I'd prefer to take a separate PR to see how best to address those.
- std::boolalpha doesn't work with llvm, so I've implemented equivalent in a couple places (not enough that it felt like worth making a helper function).
- Implement Print(ostream) as consistently as we can, as an instance member.
- This facilitates the use of the common/ostream.h template to provide operators.
- Preferring this approach so that Print is easily accessible via gdb, per suggestion on #executable-semantics.
- Switch code currently calling `type->Print(ostream)` to instead do `ostream << *type`.
- Remove the unused `PrintTypeEnv`, nothing used it and the declaration didn't match the definition.
- Move Heap and Frame/Scope to their own headers.
- Move some functions to more appropriate headers (e.g. CopyValue -> value.h).
- Define a separate Bazel rule for each header/cpp pair.
- Modify PrintValue to not print the frames of a ContinuationValue. This was necessary to break a dependency cycle between PrintValue, PrintFrame, and Action::Print.
Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>
Note this makes some structural choices that I'm not sure how popular they'll be... Most notably, I could remove `DeclarationKind` because I'm using `std::visit` and `Declaration::Visitor` in reality. I could go to `switch(tag())` instead, but I'm wondering if this approach will be well received for the separation of ownership. Alternatively, I could move `Declaration` around so that it actually implements the things like `TopLevel` -- I did feel weird with the old structure of typecheck.cpp implementing members of declaration.h, though.
Additional miscellaneous cleanup:
- Use the term "deallocate" instead of "kill" in function names, for symmetry with "allocate".
- Drop an unnecessary memory allocation in `AllocateValue`.
- Implement `PrintHeap` in terms of `PrintAddress`, so that dead values are flagged with `!!`.
* improved checking for liveness when reading and writing memory
* moving some functions to be methods of State
* finished moving functions into State
* Update executable_semantics/interpreter/interpreter.h
Co-authored-by: Geoff Romer <gromer@google.com>
* moved some comments, other minor edits
Co-authored-by: Geoff Romer <gromer@google.com>
* AST and syntax for delimited control
* stashing for later
* a little more progress
* progress on delimited continuations
* delimit, suspend, and resume implemented (draft)
* example that generates the natural numbers
* fixes
* tinkering
* changed demo to experimental
* comments and name changes
* describe delimited continuations in the README
* renamed Snapshot to Continuation, edits to comments
* Update executable_semantics/ast/statement.h
improve comment for MakeDelimitStmt
Co-authored-by: Dave Abrahams <dabrahams@google.com>
* Update executable_semantics/interpreter/interpreter.cpp
remove snake_case
Co-authored-by: Dave Abrahams <dabrahams@google.com>
* edits to comments, change name of variable
* updates to handle review edits
* trailing whitespace
* fixes to delimited continuations, added more tests, also fixed assignment to do a copy
* improvements from Geoffrey
* new test from Geoffrey, fix for empty blocks
* more suggestions from Geoffrey
* more tests for delimited continuations, renaming some of them
* renamed test files
* improve a comment
* sketch of creating continuation
* initial implementation of shift/reset style continuations
* more documentation
* fix some camel case
* implemented deep copy of continuations, added a test case for it
* fixed a bug and got the recursive test case working
* removed __delimit, polished up __continuation
* back to shallow copy for continuations
* suggestions from Geoffrey
* removed structured binding (for now)
* Update executable_semantics/ast/expression.cpp
Co-authored-by: Geoff Romer <gromer@google.com>
* responses to Geoffrey
Co-authored-by: Dave Abrahams <dabrahams@google.com>
Co-authored-by: Geoff Romer <gromer@google.com>
Making Values const allows us to separate the actual mutations (search for "*&" in this change) from places where the Value is effectively passed by-value.
* separate the alive flag from the Value class
* restored KillValue, added KillAddress
* added comments
* Update executable_semantics/interpreter/interpreter.cpp
Co-authored-by: Dave Abrahams <dabrahams@google.com>
* Update executable_semantics/interpreter/interpreter.cpp
Co-authored-by: Dave Abrahams <dabrahams@google.com>
* Update executable_semantics/interpreter/interpreter.cpp
Co-authored-by: Dave Abrahams <dabrahams@google.com>
* finish edits from Dave
Co-authored-by: Dave Abrahams <dabrahams@google.com>
* improve abstraction for AssocList, fix bug in optional else
* add flag for tracing output, clean up code for output
* turned off tracing by default, updated goldens, removed two examples that use pointers, shouldn't have been there yet
This change creates an unpleasant amount of boilerplate where `Declaration` is declared, in exchange for being able to—very pleasantly—treat it as a simple value that composes with other values everywhere it is used. Applying this technique broadly will pay off in code comprehensibility; once it has been done for all things being new'd, pointers disappear and references are only needed as an idiomatic approximation of inout. The unpleasant code grows only when new polymorphic operations are added, and then only a bit, and is an idiom whose details can readily be ignored once in place. The pleasant code pervades the codebase.
Too bad we don't have existential types in C++ ;-)
* [executable semantics] class-ify Declaration
NFC (no functional change).
Proof of concept that we can simplify code by replacing unions with safer, more
regular types. Hand-rolled existentials (type-erasing CoW wrappers) are a follow-on
step that will further simplify usage.
Began adding `const` where possible, and replacing `std::string*` with
`std::string`. Most `const`s can disappear as we replace reference semantics
with value semantics, but in the meantime it's an important step in the right
direction.
