63. Resolution of syntactic ambiguities

Level: advanced · Reading time: 21 min · Prerequisite: book/chapters/62-advanced-ebnf-reading.html · Track: supplemental · Maturity: draft · Last review: 2026-05-09

TL;DR (5 lines)

Grammar is a layered model.
A full valid program is the right teaching unit.
Invalid examples should isolate parse structure failures.
Ambiguity must be explained, not hidden.
The chapter should naturally connect to diagnostics and tests.

Frequent mistakes

Commenting each token instead of naming the grammar layer.
Confusing parse failure with type or business failure.
Skipping ambiguity notes where the same surface can be read two ways.

Prerequisites: book/chapters/62-advanced-ebnf-reading.html. See also: book/chapters/62-advanced-ebnf-reading.html, book/chapters/27-grammar.html, book/chapters/31-build-errors.html.

Concrete Problem

Grammar pages become unusable when they explain snippets without naming the parser layer or ambiguity they belong to.

Red Thread (Single Project)

One complete program is read as top-level declarations, block statements, expressions, and branch forms.

For what

This chapter helps the reader classify parser problems by grammar layer.

Work in this chapter

You will inspect one valid program, one invalid program, and the grammar layer each one exercises.

Coherent example

space demo/grammar

pick Resp {
  case Ok(value: int),
  case Err(code: int),
}

proc run(x: int) -> int {
  match x {
    case 0 { give 0 }
    else { give x }
  }
}

proc main(args: list[string]) -> int {
  give run(1)
}

export *

Complete examples

Each block below is a complete reading unit with its own boundary, data shape, and observable result.

Primary coherent example

This is the compact chapter anchor used by the surrounding explanation.

space demo/grammar

pick Resp {
  case Ok(value: int),
  case Err(code: int),
}

proc run(x: int) -> int {
  match x {
    case 0 { give 0 }
    else { give x }
  }
}

proc main(args: list[string]) -> int {
  give run(1)
}

export *

Top-level and block rules

This program shows a space declaration, a procedure block, and an entry block.

space examples/grammar/top

proc ok(value: int) -> int {
  if value < 0 { give 1 }
  give 0
}

proc main(args: list[string]) -> int {
  give ok(2)
}

export *

Pattern-oriented shape

This variant keeps match arms and returned results syntactically clear.

space examples/grammar/pattern

pick State {
  case Ready(code: int),
  case Failed(code: int),
}

proc finish(state: State) -> int {
  match state {
    case Ready(code) { give code }
    case Failed(code) { give code }
    else { give 70 }
  }
}

export *

Immediate work for this chapter

Map examples to top-level, statement, expression, and pattern layers.
Keep parse failures separate from type or domain failures.
Use grammar examples that preserve the current Vitte docs surface.
Keep the first code block complete and aligned with current Vitte docs syntax.
Keep the invalid block focused on one broken contract only.
Replace generic prose with one concrete rule visible in the code.
Keep every example small enough to review from top to bottom.

Chapter override: 63-syntactic-ambiguity-resolution.html

Dedicated problem

63. Resolution of syntactic ambiguities needs a concrete production-grade anchor around token, declaration, expression, and ambiguous edge. The page should keep the examples, diagnostics, and review rules tied to that exact boundary instead of drifting back to generic tutorial prose.

Specific complete examples

63. Resolution of syntactic ambiguities chapter anchor

The primary example is promoted here as the first chapter-specific production reading unit.

space demo/grammar

pick Resp {
  case Ok(value: int),
  case Err(code: int),
}

proc run(x: int) -> int {
  match x {
    case 0 { give 0 }
    else { give x }
  }
}

proc main(args: list[string]) -> int {
  give run(1)
}

export *

Top-level and block rules

This program shows a space declaration, a procedure block, and an entry block.

space examples/grammar/top

proc ok(value: int) -> int {
  if value < 0 { give 1 }
  give 0
}

proc main(args: list[string]) -> int {
  give ok(2)
}

export *

Pattern-oriented shape

This variant keeps match arms and returned results syntactically clear.

space examples/grammar/pattern

pick State {
  case Ready(code: int),
  case Failed(code: int),
}

proc finish(state: State) -> int {
  match state {
    case Ready(code) { give code }
    case Failed(code) { give code }
    else { give 70 }
  }
}

export *

Risks and diagnostics

Risk	Diagnostic signal	Action
Boundary drift	The chapter loses sight of token, declaration, expression, and ambiguous edge.	Restate the boundary beside the first code block and every invalid case.
Generic prose	A paragraph would still be true in another chapter.	Replace it with a code-specific rule from this page.
Weak diagnostic	The failure does not point back to the chapter contract.	Reduce the invalid case until one failure explains the rule.

Review checklist

The first example is complete and aligned with Vitte docs syntax.
The production section names where this construct belongs in real code.
The risk table connects each failure to a diagnostic or review action.
The avoid list rejects broad misuse without adding quiz-like prompts.

Production use

Use this chapter when a code review needs to preserve token, declaration, expression, and ambiguous edge.
Keep examples small enough to copy into fixtures or docs smoke tests.
Treat the invalid case as regression material for future docs checks.

What to avoid

Do not add a second topic that hides the chapter's main contract.
Do not expand examples by adding unrelated subsystems.
Do not rely on prose when a small Vitte block can show the rule.

Global explanation

Grammar should be read by layer: top-level declarations, block statements, expressions, patterns, and ambiguity points. The reader should leave able to say what sort of parser expectation has failed.

Invalid case

proc broken(x: int) -> int {
  match x
    case 0 { give 0 }
  }
}

This invalid case is intentionally small. It exists to isolate the contract failure that the chapter is trying to teach.

Common pitfalls

Commenting each token instead of naming the grammar layer.
Confusing parse failure with type or business failure.
Skipping ambiguity notes where the same surface can be read two ways.

Short exercise

Take the valid example and identify one top-level rule, one statement rule, and one expression rule it exercises.

Summary in 5 points

Grammar is a layered model.
A full valid program is the right teaching unit.
Invalid examples should isolate parse structure failures.
Ambiguity must be explained, not hidden.
The chapter should naturally connect to diagnostics and tests.

Next best action

Extend the coherent example by one small, justified step and keep the same contract visible from input to output.

Chapter deep dive

63. Resolution of syntactic ambiguities connects grammar rules to parser expectations. The chapter is written for a reader explaining why one parse path is valid.

The practical boundary is: token, declaration, expression, and ambiguous edge. Keep that boundary in view while reading the example, the invalid case, and the exercise.

Role in the learning path

Grammar pages become unusable when they explain snippets without naming the parser layer or ambiguity they belong to.

One complete program is read as top-level declarations, block statements, expressions, and branch forms.

This chapter helps the reader classify parser problems by grammar layer.

Profile-specific deep dive

Grammar layer

Top-level items, statements, expressions, patterns, and types should be identifiable.
A parser failure should not be explained as a business rule failure.
Ambiguity notes should name the two possible readings.

Valid and invalid surface

Use one full valid program as the reference shape.
Use one invalid fragment that breaks a single grammar layer.
Keep examples aligned with the current Vitte docs syntax.

Reading the valid example

space demo/grammar: names the ownership boundary before any behavior appears.
pick Resp {: makes possible outcomes explicit instead of encoding them as magic values.
case Ok(value: int),: names one outcome that callers must be ready to handle.
case Err(code: int),: names one outcome that callers must be ready to handle.
}: keeps the syntactic shape visible for parser reasoning.
proc run(x: int) -> int {: states the callable contract: inputs first, result shape last.
match x {: keeps the syntactic shape visible for parser reasoning.
case 0 { give 0 }: names one outcome that callers must be ready to handle.
else { give x }: keeps the syntactic shape visible for parser reasoning.
}: keeps the syntactic shape visible for parser reasoning.
}: keeps the syntactic shape visible for parser reasoning.
proc main(args: list[string]) -> int {: states the callable contract: inputs first, result shape last.
give run(1): ends the local path with an explicit result.
}: keeps the syntactic shape visible for parser reasoning.
export *: keeps the syntactic shape visible for parser reasoning.

Lesson from the invalid example

proc broken(x: int) -> int {: this line helps isolate the failure because it states the callable contract: inputs first, result shape last.
match x: this line helps isolate the failure because it keeps the syntactic shape visible for parser reasoning.
case 0 { give 0 }: this line helps isolate the failure because it names one outcome that callers must be ready to handle.
}: this line helps isolate the failure because it keeps the syntactic shape visible for parser reasoning.
}: this line helps isolate the failure because it keeps the syntactic shape visible for parser reasoning.

Engineering decisions to preserve

Name the boundary before changing code: Grammar is a layered model.
Keep the smallest example executable: A full valid program is the right teaching unit.
Make the invalid path explain one failure only: Invalid examples should isolate parse structure failures.
Prefer a visible contract over an implied convention: Ambiguity must be explained, not hidden.
Leave a review anchor that another maintainer can verify: The chapter should naturally connect to diagnostics and tests.

Context-specific review criteria

The page makes the token, declaration, expression, and ambiguous edge boundary visible before the first code block.
The intended reader, a reader explaining why one parse path is valid, can follow the valid example through named contracts instead of memorized tokens.
The invalid example fails for the same reason the prose discusses.
The exercise extends the same contract instead of introducing an unrelated concept.
The next chapter can reuse the vocabulary introduced here without redefining it.
The chapter stays specific enough that its title materially changes the meaning of the page.
Every warning connects to a concrete code shape.
The summary leaves one durable engineering rule behind.

Contract matrix

Concern	Chapter rule	Evidence to keep
Ownership	Code belongs behind the boundary named by the chapter.	The chapter keeps ownership visible through token, declaration, expression, and ambiguous edge.
Input contract	The procedure receives a shape that is named before branching.	The valid example names the accepted shape before branching.
Nominal path	The clean path remains readable without hidden state.	The successful result can be found without reading hidden state.
Failure path	The invalid case isolates one failure reason.	The broken example has one main reason to fail.
Naming	Names explain the domain rather than only the mechanism.	Names remain tied to the chapter goal.
Types	Types remove ambiguity from values and results.	Fields and return values carry domain meaning.
Control flow	Branches stay traceable from guard to result.	Guards appear before the result they protect.
Module boundary	The public surface stays smaller than implementation detail.	The public surface remains smaller than the implementation detail.
Diagnostic value	The failure path points back to the exact contract.	The invalid example points back to the exact contract.
Test value	Regression evidence covers one passing path and one failing path.	One passing case and one failing case cover the lesson.
Refactor value	Implementation cleanup preserves the result shape.	The result shape stays stable during local cleanup.
Publication value	The chapter leaves one concrete engineering rule.	The chapter leaves one concrete engineering rule.

Rewrite path for this chapter

Rewrite the opening paragraph so it names token, declaration, expression, and ambiguous edge before naming syntax.
Keep the valid example small enough that the full contract fits on screen.
Move any broad claim back to a specific line in the example.
Preserve one invalid case that fails for the chapter's main reason.
Add one sentence explaining why the invalid case is not a random error.
Make every pitfall actionable by naming the code shape it damages.
Keep the exercise inside the same domain as the example.
Avoid introducing a second unrelated project just to show variety.
Use the summary to restate the chapter rule, not the table of contents.
Check that the next chapter can build on this vocabulary.
Remove any sentence that would still be true in every other chapter.
Keep the last action small, local, and testable.

Diagnostic anchors

The first inspected line is the one that declares the chapter's main contract.
The central type, field, procedure, or branch carries the chapter's main idea.
The invalid example includes a sentence-level explanation of its failure.
Refactors preserve the detail that would otherwise mislead a future reader.
The behavior that must stay stable is named before implementation changes begin.
Vague names are replaced before they become review friction.
Regression coverage protects the chapter's main contract.
Implementation details stay out of public API unless the chapter explicitly teaches that surface.
Beginner-facing diagnostics point to the contract, not to a random syntax detail.
The next chapter can assume one clearly named concept from this page.

When extending this chapter

Extend toward a reader explaining why one parse path is valid, not toward a broader catalog of features.
Add a second example only if it sharpens the same contract.
Prefer a small variant over a new subsystem.
Keep prose close to code; every abstract claim should point to a visible shape.
Do not hide a new concept in the exercise.
If a paragraph explains policy, add the concrete code boundary it protects.
If a paragraph explains syntax, add the semantic reason the syntax matters.
If a paragraph explains architecture, identify the owner of each boundary.
If a paragraph explains failure, keep the failing line close to the explanation.
Stop expanding when the chapter has one complete, testable lesson.

Failure modes to avoid

Commenting each token instead of naming the grammar layer.
Confusing parse failure with type or business failure.
Skipping ambiguity notes where the same surface can be read two ways.

Practice scenario

Start from the coherent example in 63. Resolution of syntactic ambiguities. Change one identifier, one guard, and one returned value. After each change, write down whether the public contract is still the same contract or a new one.

If the contract changed, update the type or result shape first. If only the implementation changed, keep the external name stable and add one regression note explaining what should not change again.

Before moving on

You can state the chapter role: connects grammar rules to parser expectations.
You can point to the main boundary: token, declaration, expression, and ambiguous edge.
You can connect the invalid case to the problem statement: Grammar pages become unusable when they explain snippets without naming the parser layer or ambiguity they belong to.
You can perform the exercise: Take the valid example and identify one top-level rule, one statement rule, and one expression rule it exercises.