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feat: top-level constants; fix a type that a function body fixes late - #441
The grammar had the declaration (const_decl), and only the core parser read it.
Step
Before
Now
Surface parser
"Unexpected declaration: const_decl"
SurfaceDecl::Const
Type checker
the value was not checked, and no function body had the constant in scope
the value is checked, and each function body sees the constant
wasm
no code; a use of the name was a trap
a function with no parameter; a use is a call
Interpreter
no code
the value, from an empty environment
The rules:
Scope. The value of a constant sees the functions of the module and the constants before it. Each function sees each constant. A let or a parameter of the same name hides the constant.
Type. The type in the declaration, or else the type of the value. A linear type is an error (a constant is used many times). A value that does not fix the type (let K = None) is an error that asks for a type in the declaration.
Modules. A constant is private to its module (the grammar has no pub for it). 2 modules can have a constant of one name: in the merge, a constant gets a module name as a function does.
Evaluation. The value is computed at each use. A value that is costly, or that has an effect that must happen 1 time, needs a wasm global that a start function sets. The code names that step.
Upper-case names. The parser reads a name with an upper-case first letter as a constructor. Such a name that is no constructor in scope, and that is a constant of the module, is the constant. A constructor of the same name comes first.
One declaration for a name. A module declares a name 1 time, as a function or as a constant. This also refuses 2 functions of one name, which passed the checker and then gave a wasm module that was not valid ("duplicate export name").
The forms behind --unstable-core are behind it in the value of a constant too.
2. Fix: a type that a function body fixes late
data Option(a) = None | Some(a)
fn main(): I64 = let o = None in match o of | None => 5000000000 | Some(n) => n end
check accepted this program, and run then stopped: "emitted wasm failed structural validation: type mismatch: expected i64, found i32". The validator stopped the module, so no wrong program ran.
Cause: the arms of the match fix the type of o after the checker recorded the type of the scrutinee. The solutions of a function body were dropped at the end of its check, before the type table was resolved, so the table kept the type as not known and the wasm backend read the payload as an i32. Before #439 this program did not pass the checker, so the gap was not reachable.
The types of a body are now resolved when its check ends.
Verification
cargo test --workspace --no-fail-fast: 642 passed, 0 failed. No program of the corpus changed.
cargo fmt --all --check and cargo clippy --workspace --all-targets: clean.
scripts/status-gate.sh: 639 all-target tests (4 more than before).
scripts/probe-battery.sh: 51 SAME, 7 SKIP (the SKIP rows need the wasmtime CLI).
New file constants.rs, each program as wasm and in the interpreter:
a_top_level_constant_runs (10 programs: plain, lower-case with a type, order, in a lambda, hidden by a local, I64 and F64 and Bool, a closure and a pair and a list and a data value, a generic function, a constructor of the same name, a function value);
1. Top-level constants: `let K = 40` and `let K: I32 = 40`.
The grammar had the declaration, and only the core parser read it. The
surface parser refused it ("Unexpected declaration: const_decl"), the
type checker did not check its value, no function body had it in scope,
and no backend had code for it (a use of its name was a trap in wasm).
A constant is now a value that each function of its module can name.
- Its value sees the functions of the module and the constants before
it. Its type is the type in the declaration, or else the type of its
value. A type that is linear, or that the value does not fix, is an
error by name.
- A constant is private to its module. In the merge of a program it
gets a module name as a function does.
- Its value is computed at each use: in wasm a constant is a function
with no parameter, and the interpreter evaluates the value from an
empty environment. A local of the same name hides the constant.
- The parser reads a name with an upper-case first letter as a
constructor. Such a name that is no constructor in scope, and that is
a constant of the module, is the constant.
- A module declares a name 1 time, as a function or as a constant.
2 functions of one name gave a wasm module that was not valid.
2. Fix: a type that a function body fixes after the expression was
checked stayed a variable in the type table, because the solutions of a
body were dropped before the table was resolved. `let o = None in match
o of | None => 5000000000 | Some(n) => n end` passed `check` and then
gave a wasm module that was not valid. #439 made this program pass the
checker. The types of a body are now resolved when its check ends.
Tests: constants.rs (4 tests: 10 programs as wasm and in the
interpreter, the module rule, the flag, 8 refused programs), and 2 more
programs in a_constructor_gets_its_type_arguments_from_its_use.
642 tests pass; the all-target count is 639.
Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0136P7ZmKrYLDC4WHi2yt11u
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Reviewing files that changed from the base of the PR and between 92645c7 and 9c7f51d.
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src/ephapax-cli/tests/constants.rs
Summary
Summary by CodeRabbit
New Features
Added support for module-level constants, including optional type annotations and references from other constants and functions.
Constants are supported in both compiled and interpreted execution.
Improved type inference for None values matched against Option variants in compiled and interpreted execution.
Tests
Expanded coverage for constant values, types, scope, name resolution, privacy and invalid declarations.
Updated the documented all-target test total from 635 to 639.
The change adds module-level constants across parsing, desugaring, qualification, type checking, monomorphisation, interpreter evaluation and WebAssembly generation. It adds CLI tests for runtime behaviour and invalid declarations, adds two constructor-inference tests, and updates the documented all-target test count from 635 to 639.
The surface declaration and parser now represent module-level constants. Desugaring preserves declarations and resolves constant names separately from constructors. Qualification and cross-module collision checks include constants.
Check and monomorphise constants src/ephapax-typing/src/lib.rs, src/ephapax-typing/src/mono.rs
Module checking detects duplicate function and constant names, checks constants in declaration order, and rejects unresolved or linear types. Monomorphisation rewrites constant values as well as function bodies.
Evaluate constants in both execution paths src/ephapax-interp/src/lib.rs, src/ephapax-wasm/src/lib.rs
The interpreter registers and evaluates constant expressions. WebAssembly generation emits constants as zero-parameter functions and calls them for constant references.
Validate constant behaviour and document test count src/ephapax-cli/tests/constants.rs, src/ephapax-cli/tests/run_wasm.rs, TEST-NEEDS.adoc
CLI tests cover constant values and errors in compiled and interpreted modes, plus constructor type inference. The documented all-target test count changes from 635 to 639.
This change adds module-level constants across the parser, type checker, interpreter and wasm backend, and fixes a wasm type-resolution defect. No actionable merge-blocking risk was identified in the supplied evidence.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
Check name
Status
Explanation
Resolution
Docstring Coverage
Docstring coverage is 71.43% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
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Status
Explanation
Title check
The title clearly identifies the main change, top-level constants, and the related function-body type-resolution fix.
Description check
The description explains both changes, their behaviour, and the reported verification. It is directly related to the changeset.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
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Check skipped because no linked issues were found for this pull request.
Full details: Docstring Coverage
Explanation
Docstring coverage is 71.43% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 21 functions across 11 files. (1 skipped: 1 unsupported.)
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
Finishing Touches
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Failed pre-merge checks:
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Write docstrings for the functions missing them to satisfy the coverage
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Files selected for processing: 12
TEST-NEEDS.adoc
src/ephapax-cli/tests/constants.rs
src/ephapax-cli/tests/run_wasm.rs
src/ephapax-desugar/src/lib.rs
src/ephapax-driver/src/lib.rs
src/ephapax-driver/src/qualify.rs
src/ephapax-interp/src/lib.rs
src/ephapax-parser/src/surface.rs
src/ephapax-surface/src/lib.rs
src/ephapax-typing/src/lib.rs
src/ephapax-typing/src/mono.rs
src/ephapax-wasm/src/lib.rs
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Summary
let K = 40andlet K: I32 = 40.1. Top-level constants
The grammar had the declaration (
const_decl), and only the core parser read it.SurfaceDecl::ConstThe rules:
letor a parameter of the same name hides the constant.let K = None) is an error that asks for a type in the declaration.pubfor it). 2 modules can have a constant of one name: in the merge, a constant gets a module name as a function does.The forms behind
--unstable-coreare behind it in the value of a constant too.2. Fix: a type that a function body fixes late
checkaccepted this program, andrunthen stopped: "emitted wasm failed structural validation: type mismatch: expected i64, found i32". The validator stopped the module, so no wrong program ran.Cause: the arms of the
matchfix the type ofoafter the checker recorded the type of the scrutinee. The solutions of a function body were dropped at the end of its check, before the type table was resolved, so the table kept the type as not known and the wasm backend read the payload as an i32. Before #439 this program did not pass the checker, so the gap was not reachable.The types of a body are now resolved when its check ends.
Verification
cargo test --workspace --no-fail-fast: 642 passed, 0 failed. No program of the corpus changed.cargo fmt --all --checkandcargo clippy --workspace --all-targets: clean.scripts/status-gate.sh: 639 all-target tests (4 more than before).scripts/probe-battery.sh: 51 SAME, 7 SKIP (the SKIP rows need the wasmtime CLI).constants.rs, each program as wasm and in the interpreter:a_top_level_constant_runs(10 programs: plain, lower-case with a type, order, in a lambda, hidden by a local, I64 and F64 and Bool, a closure and a pair and a list and adatavalue, a generic function, a constructor of the same name, a function value);a_constant_is_private_to_its_module;a_constant_follows_the_flag;a_constant_that_is_not_valid_is_refused_by_name(8 programs).a_constructor_gets_its_type_arguments_from_its_use: 2 more programs for the fix (I64 and F64).Generated by Claude Code