Keyword at

Definition

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

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

Grammatical role

Attaches an entry or declaration to an explicit logical or modular location.

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

Canonical syntax

Canonical form: `entry name at module/path { ... }`.

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

Detailed semantics

Semantically, at 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, at 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

at 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 at 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

• `entry name at module/path { ... }`.

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

entry main at core/app {
  return 0
}

This example shows at 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 at, not the isolated word.
2. Then identify which contract becomes visible because of at: type, branch, binding, module, exit, or advanced boundary.
3. Finish by checking the observable effect produced by the construction that contains at.

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

Comparison with C

/* C comparison: entry attachment is usually implied by main and linker layout. */

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

at 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 at 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 at when another, more precise keyword already carries the block's intent.
• Avoid at 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 at 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

entry main core/app {
  return 0
}

The attachment surface is incomplete because the entry form is missing its connector.

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 at is moved, truncated, or combined with the wrong context. Concretely, the logical attachment is missing or badly connected to the declaration it completes.

A good encyclopedic counter-example does not show arbitrarily broken code: it isolates the precise reason why at 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 at 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: at is better understood when one knows precisely what it does not do.

Common misreadings

• Reducing at 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/21-cli-project.html
• docs/book/chapters/27-grammar.html
• docs/book/chapters/31-build-errors.html

See also

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