Keyword emit

Definition

emit is a Vitte keyword whose role must remain explicit in both grammar and program contract.

The keyword emit belongs to Vitte's structural vocabulary. Its correct reading depends on the overall contract of the block in which it appears.

Grammatical role

Participates in the general grammar of the language.

This grammatical role is essential: if a reader understands the structural place of emit, they already understand much of the diagnostics that will appear when it is moved or truncated.

Canonical syntax

Canonical form: use `emit` only in its valid grammatical role.

The canonical form matters because it gives the compiler and the reader the same reference structure. A large share of diagnostics related to emit come from an abbreviated, displaced, or incomplete form.

Detailed semantics

Semantically, emit changes how the whole construction is read. Its real meaning appears only in relation to the surrounding grammar and the effect produced on the program.

In an encyclopedic reading, emit should not be reduced to a dictionary definition. Its effect on scope, block shape, value visibility, control progression, and the diagnostic family it activates when misused must also be considered.

Effect on execution

emit changes the interpretation of the construction where it appears and should therefore be read with the block's global effect in mind.

In other words, the presence of emit is not merely syntactic: it helps the reader predict what will be executed, produced, exposed, or forbidden from this point in the program.

Valid variants

• use `emit` only in its valid grammatical role.

These variants are not free synonyms. They indicate the legitimate forms from which one can reason about diagnostics, scope differences, or contract readability.

Vitte example

proc sample_emit(x: int) -> int {
  give x
}

This example shows emit in a nominal context. It should be read globally: where the contract begins, which values are constrained, which output becomes observable, and why the presence of the keyword is justified.

Guided reading of the example

1. First locate the full construction that contains emit, not the isolated word.
2. Then identify which contract becomes visible because of emit: type, branch, binding, module, exit, or advanced boundary.
3. Finish by checking the observable effect produced by the construction that contains emit.

This guided reading is intentionally closer to a reference page than to a tutorial: it helps reconstruct the exact role of emit in a complete block.

Comparison with C

/* C comparison: the same intent is usually expressed with a simpler token surface. */

For this keyword, the parallel with C remains approximate. The comparison mainly indicates that in C the same idea is often spread across file conventions, operators, or less explicit control structures.

The source of truth remains Vitte grammar and semantics. The comparison with C should be read as a cultural marker, not as a parallel specification.

Recommended uses

emit deserves to appear when it simplifies the reading of the block's global contract, not when it merely adds one more surface form.

When to use it

• When emit makes the block contract more explicit at first reading.
• When it reduces the number of implicit assumptions the reader must reconstruct mentally.
• When its presence genuinely clarifies the grammar and intent of the block.

When to avoid it

• Avoid emit when another, more precise keyword already carries the block's intent.
• Avoid emit when it adds only surface noise without clarifying the contract.
• Avoid reading or teaching it as an isolated token with no relation to the full structure.

Common pitfalls

• Using emit in a grammatical layer where it does not belong.
• Confusing the role of the keyword with the role of the full surrounding block.
• Showing only the nominal form and never how the contract fails.

Invalid example and diagnostic

proc bad_emit() -> int {
  emit
  give 0
}

The keyword is used outside its valid grammatical or contractual context.

The counter-example is not merely wrong: it is wrong in an instructive way. It shows which grammar or execution-contract assumption is no longer accepted when emit is moved, truncated, or combined with the wrong context. Concretely, the contract expected by the construction is no longer respected.

A good encyclopedic counter-example does not show arbitrarily broken code: it isolates the precise reason why emit can no longer support the expected contract. Its teaching value is diagnostic before it is syntactic.

Common compilation errors

This table does not replace the compiler's exact diagnostics. It serves as a mental map: when emit fails, the problem usually comes from an invalid grammatical form, an incoherent type contract, or an incomplete construction.

Neighbor keywords

Comparison with neighboring keywords is essential on a wiki-style page: emit is better understood when one knows precisely what it does not do.

Common misreadings

• Reducing emit to a local token instead of reading it as part of a full construction.
• Explaining only the syntax and forgetting the reading or diagnostic contract it imposes.

Implementation and diagnostic notes

• A useful diagnostic for this keyword should always connect the observed syntax to the expected contract.
• From the compiler's point of view, this keyword should remain identifiable early enough to produce coherent, localized messages.

Presence in the book

• docs/book/chapters/27-grammar.html
• docs/book/chapters/31-build-errors.html
• docs/book/chapters/34-compiler-mental-model.html

See also

• docs/book/chapters/keywords/erreurs-compilateur.html
• docs/book/chapters/keywords/proc.html
• docs/book/glossary.html