Keyword or

Definition

or is an operator keyword that changes how values are combined, tested, or traversed.

The keyword or participates in a relation between values or in the logical reading of an expression. It should not be read in isolation, but as an operator that changes the meaning of the whole expression.

Grammatical role

Combines two logical expressions by accepting that at least one is valid.

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

Canonical syntax

Canonical form: `left or right`.

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

Detailed semantics

Semantically, or only makes sense with its operands and the surrounding form. The full expression must be read to understand the logical or structural contract it imposes.

In an encyclopedic reading, or 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

or acts at expression level by changing the logical or structural result computed at that exact point.

In other words, the presence of or 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

• `left or right`.

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 either(a: bool, b: bool) -> bool {
  give a or b
}

This example shows or 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 or, not the isolated word.
2. Then identify which contract becomes visible because of or: type, branch, binding, module, exit, or advanced boundary.
3. Finish by checking the observable effect produced by the construction that contains or.
4. For an operator keyword, reread the full expression to avoid an overly local interpretation.

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

Comparison with C

/* C comparison: this role is usually expressed with operators or explicit loops and conditionals. */

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

or 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 or makes the block contract more explicit at first reading.
• When it reduces the number of implicit assumptions the reader must reconstruct mentally.
• When a logical or structural relation must be read as an integral part of the expression.

When to avoid it

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

The operator surface is incomplete because it is missing the operands or the valid surrounding construct.

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 or is moved, truncated, or combined with the wrong context. Concretely, the logical operator does not have all the operands it needs.

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

Common misreadings

• Reducing or 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

• The most useful diagnostics signal missing operands, an incompatible value category, or a reading ambiguity.
• In the front-end, these keywords influence expression hierarchy and sometimes precedence rules.

Presence in the book

• docs/book/chapters/05-types.html
• docs/book/chapters/07-control.html
• docs/book/chapters/27-grammar.html

See also

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