Keyword `bool`

bool is documented here as a full reference entry: grammatical role, semantics, canonical form, valid example, counter-example, diagnostics, interactions, and design notes.

Visual anchor: each page now has its own wiki-style profile image. It shows a small code excerpt where bool appears in its most recognizable form.

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Summary

Overview
Definition
Grammatical role
Canonical syntax
Detailed semantics
Effect on execution
Valid variants
Vitte example
Guided reading of the example
Comparison with C
Recommended uses
Invalid example and diagnostic
Common errors
Neighbor keywords
Common misreadings
Implementation notes
Presence in the book

Overview

Field	Value
Keyword	`bool`
Family	Built-in type
Suggested level	Beginner
Main neighbor	`int`
Short role	`bool` is a built-in type keyword used to make a value contract explicit.
Main effect	`bool` does not directly modify control flow; it restricts what the program may legally produce, consume, or transform.

The keyword bool makes a value contract explicit in a signature, local declaration, or data structure. Its main role is not decorative: it bounds what the compiler and the reader may expect from an expression.

A useful encyclopedic reading should answer three questions: where can bool appear, what does it change in the block contract, and how does the compiler signal misuse?

Definition

bool is a built-in type keyword used to make a value contract explicit.

Grammatical role

Specifies the language's boolean type.

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

Canonical syntax

Canonical form: `let ok: bool = true`.

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

Detailed semantics

Semantically, bool is not just a type name: it constrains operation compatibility, assignment validity, and return shapes. As soon as it appears, the reader should check which operations become legal and which conversions become forbidden.

In an encyclopedic reading, bool 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

bool does not directly modify control flow; it restricts what the program may legally produce, consume, or transform.

In other words, the presence of bool 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

`let ok: bool = true`.

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 can_run(enabled: bool) -> int {
  if enabled { give 0 }
  give 1
}

This example shows bool 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

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

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

Comparison with C

int can_run(_Bool enabled) {
  if (enabled) return 0;
  return 1;
}

This C comparison is structural: it aligns the role of the keyword with a familiar surface without claiming that the two languages carry exactly the same contracts.

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

bool 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 bool makes the block contract more explicit at first reading.
When it reduces the number of implicit assumptions the reader must reconstruct mentally.
When a signature must state the nature of the manipulated data clearly.

When to avoid it

Avoid bool when another, more precise keyword already carries the block's intent.
Avoid bool 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 bool 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_bool() -> int {
  let enabled: bool = 1
  if enabled { give 0 }
  give 1
}

The boolean contract is broken because the declaration does not use a boolean value.

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 bool is moved, truncated, or combined with the wrong context. Concretely, the boolean contract breaks because the declaration does not use an explicit boolean value.

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

Common compilation errors

Typical message	Usual cause	Fix
`unexpected token near bool`	The keyword appears in an invalid form or grammatical layer.	Return to the canonical form and verify placement and delimiters.
`type mismatch`	The keyword participates in a block whose value contract is incoherent.	Realign the surrounding types, branches, or produced values.
`invalid construct`	The keyword is present but the surrounding construction is incomplete.	Restore the missing branch, declarative part, or operands.

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

Neighbor keywords

Keyword	Operational difference
`int`	Direct neighboring keyword: it helps explain what `bool` does, either by contrast or by complement.

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

Common misreadings

Reducing bool 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.

Keyword bool