Keyword asm

Definition

asm marks an advanced surface where low-level or unsafe behavior must remain explicit.

The keyword asm marks a zone where the language deliberately exposes a riskier or more machine-facing surface. Its value is precision, not convenience.

Grammatical role

Introduces an assembly block or machine escape hatch.

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

Canonical syntax

Canonical form: `asm { ... }`.

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

Detailed semantics

Semantically, asm opens a strongly explicit zone. It signals that a safety, low-level, or interoperability assumption is no longer implicit and must be owned openly.

In an encyclopedic reading, asm 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

asm opens a zone where the real effect may touch memory, the ABI, or machine instructions. It should be read as a boundary of strong responsibility.

In other words, the presence of asm 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

• `asm { ... }`.

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 tick() -> int {
  asm {
    "nop"
  }
  give 0
}

This example shows asm 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 asm, not the isolated word.
2. Then identify which contract becomes visible because of asm: type, branch, binding, module, exit, or advanced boundary.
3. Finish by checking the observable effect produced by the construction that contains asm.
4. For an advanced surface, explicitly verify the safety or interoperability boundary it opens.

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

Comparison with C

/* C comparison: this role usually appears through inline assembly or unsafe pointer manipulation. */

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

asm 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 asm makes the block contract more explicit at first reading.
• When it reduces the number of implicit assumptions the reader must reconstruct mentally.
• When a low-level boundary must be marked explicitly instead of being hidden.

When to avoid it

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

The advanced surface is malformed because it lacks the enclosing contract required by the language.

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 asm is moved, truncated, or combined with the wrong context. Concretely, the machine block does not receive the expected structure.

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

Common misreadings

• Reducing asm 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

• Diagnostics must stay precise, because a poorly documented advanced surface quickly creates expensive-to-debug errors.
• In a compiler, these keywords often act as guard rails around unsafe transformations or calls.

Presence in the book

• docs/book/chapters/16-interop.html
• docs/book/chapters/27-grammar.html
• docs/book/chapters/65-abi-and-vitte-interop-contracts.html

See also

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