📐mlab-ast

The groupant beside mlab/src/ast.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.

Facts

Components

Obernants

The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.

Model text

descriptant

Expression and statement representation

Expr is a tagged recursive sum: Num/Imag retain value and spelling, Str retains quote mode, Binary retains BinOp, Range retains optional step, Index retains argument order, AnonFn retains Rc body. Stmt stores one-based lexer line plus print/op metadata. Program partitions top-level statements and Rc function definitions.

Modeling epoch 2026-10-31

Prospective source reading precedes test additions. Retained observations: parser constructs these nodes; interp and vm consume them. Preserving End versus Ident(end), matrix rows and Pow versus EPow is required at that join; flattening any of them loses semantics.

This is partial source-derived modeling, not proof, full semantic coverage, or a performance result. Public malformed representations, unbounded allocations and exhaustive numerical edge cases remain outside the checked fixtures.

approximant

Expression and statement representation forward relation

Expr is a tagged recursive sum: Num/Imag retain value and spelling, Str retains quote mode, Binary retains BinOp, Range retains optional step, Index retains argument order, AnonFn retains Rc body. Stmt stores one-based lexer line plus print/op metadata. Program partitions top-level statements and Rc function definitions.

Domain: Finite enum trees and ordered vectors; f64 payload permits NaN/Infinity. Public construction does not certify well-formed programs. No I/O or GPU effects.

No executable Rust surrogate is supplied: categorical decisions require exact observations; numerical kernels have no measured approximation metric here. Future supported caps are 1%, 2%, 5%, 10% only.

invariant

Invariant and cost

Cloning Expr preserves payload and child order; Rc clones share anonymous bodies. Program::default has empty body/functions. Operator text uses != for Ne, which collapses source spellings ~= and != after lexing.

Cost: Clone traverses owned tree vectors/boxes and strings, O(owned nodes+text), but Rc body/function references clone O(1). text is O(1). No recursion depth cap.

Failure ordering: There is no fallible AST validation API. Allocation/recursive clone can fail externally; text exhaustively maps BinOp. Representation checks must not be reported as execution coverage.

composition

Parent composition

parser constructs these nodes; interp and vm consume them. Preserving End versus Ident(end), matrix rows and Pow versus EPow is required at that join; flattening any of them loses semantics.

Scoped fragments are projections over exact byte intervals in this source; they share one parent syntax projection. Uncovered declarations and embedded checks remain parent modeled. There is no fallible AST validation API. Allocation/recursive clone can fail externally; text exhaustively maps BinOp. Representation checks must not be reported as execution coverage.

The relation is source-derived and finite checks cannot establish complete correctness or a composition-wide numerical error bound.

models

behavior_complement

The representation relation excludes clone changing tags, ordered children, names or literal payload. BinOp::Pow and EPow are distinct even where scalar execution agrees. It does not exclude a hand-constructed invalid assignment or nonsensical line number; enums do not enforce grammar or evaluation.

reverse_reconstruction

Given an Expr, compatible source strings are all texts parsed to its retained tags/payload; whitespace/comments are not uniquely recoverable. Clone's antecedent is any structurally equal tree; Rc anonymous-body cloning additionally retains pointer identity, not a fresh allocation. Runtime values cannot recover arbitrary syntax.

representation_transport

Cloning Expr preserves payload and child order; Rc clones share anonymous bodies. Program::default has empty body/functions. Operator text uses != for Ne, which collapses source spellings ~= and != after lexing.

failure_precedence

There is no fallible AST validation API. Allocation/recursive clone can fail externally; text exhaustively maps BinOp. Representation checks must not be reported as execution coverage.

resource_domain

Finite enum trees and ordered vectors; f64 payload permits NaN/Infinity. Public construction does not certify well-formed programs. No I/O or GPU effects.

interaction_relation

parser constructs these nodes; interp and vm consume them. Preserving End versus Ident(end), matrix rows and Pow versus EPow is required at that join; flattening any of them loses semantics.

tests

Source-specific bounded evidence

ast::wave30::representation: Rc clone sharing, End/Colon child preservation, operator distinction, empty Program.

Seven named tests each passed twice debug and twice release on 2026-10-31, with actual named log lines sorted and identical across all four runs (28 selected successful executions). Each source has a compiled changed-assertion negative control; six runtime sources additionally have compiled production-body mutants that fail those unchanged tests. AST has representation evidence only. Every mutant is byte-restored and its positive test rerun. See evidence.json for this source's exact hash, mutation and exit statuses. External receipts retain full logs, command metadata, control records and prospective notes.

Unexecuted here: Representation only; AST is not an evaluator. No corpus, GPU, live filesystem, timer or callback run. No broad Clippy claim; dependency/style checks were not repeated. Only appended test blocks were rustfmt-formatted; original production bytes are unchanged.

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