Keyword as

Definition

as is a module-surface keyword used to organize visibility, imports, or sharing.

The keyword as organizes symbol circulation across modules. It clarifies what is imported, shared, renamed, or attached to a visibility boundary.

Grammatical role

Renames an import, symbol, or attachment locally.

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

Canonical syntax

Canonical form: `... as alias`.

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

Detailed semantics

Semantically, as modifies symbol visibility. It influences how a reader reconstructs the origin of names and how the compiler resolves references.

In an encyclopedic reading, as 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

as acts mainly on name resolution and cross-module visibility. Its execution-time effect is indirect but decisive for the structure of the compiled code.

In other words, the presence of as 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

• `... as alias`.

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

space app/core
use std.io.{read} as io

proc ping() -> int {
  give 0
}

This example shows as 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 as, not the isolated word.
2. Then identify which contract becomes visible because of as: type, branch, binding, module, exit, or advanced boundary.
3. Finish by checking the observable effect produced by the construction that contains as.
4. For a module keyword, verify the origin and destination of visible symbols.

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

Comparison with C

/* C comparison: imports are usually done with includes and naming conventions instead of module aliases. */

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

as 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 as makes the block contract more explicit at first reading.
• When it reduces the number of implicit assumptions the reader must reconstruct mentally.
• When the origin or outward exposure of a symbol must stay visible at module level.

When to avoid it

• Avoid as when another, more precise keyword already carries the block's intent.
• Avoid as 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 as 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_as() -> int {
  as
  give 0
}

The module-level surface is misplaced or incomplete.

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 as is moved, truncated, or combined with the wrong context. Concretely, the renaming is not attached to the construction that supplies the alias.

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

Common misreadings

• Reducing as 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

• Common errors concern name resolution, alias collisions, or a shared surface that is too broad or incomplete.
• In a compiler, these keywords participate in cross-file resolution and visible API construction.

Presence in the book

• docs/book/chapters/09-modules.html
• docs/book/chapters/17-stdlib.html
• docs/book/chapters/27-grammar.html

See also

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