@strict Directive

Control strict type checking.

Syntax

@strict true   # Enable strict checking (default)
@strict false  # Relax some checks

Default Behavior

@strict true is the default. It enables:

• Unresolved symbol reporting
• Type mismatch detection
• Effect declaration requirements
• Constraint validation
• Effect compatibility checking

Strict Mode

@strict true

cell a() -> String / {http}
  return fetch()
end

cell b() -> String        # ERROR: Undeclared effect {http}
  return a()
end

Fix by declaring:

@strict true

cell a() -> String / {http}
  return fetch()
end

cell b() -> String / {http}  # OK
  return a()
end

Relaxed Mode

With @strict false:

@strict false

# Some checks are relaxed
# Useful for documentation snippets

What Strict Mode Checks

Check	Strict	Relaxed
Unresolved symbols	Error	Warning
Type mismatches	Error	Warning
Undeclared effects	Error	Allowed
Effect compatibility	Error	Allowed
Constraint violations	Error	Runtime

When to Use Relaxed

Use @strict false for:

• Documentation — Example snippets
• Prototyping — Quick experiments
• Learning — Beginner tutorials

Example: Documentation Snippet

@strict false

# This is for documentation
# Some types may not be defined

cell example(data: CustomType) -> String
  return process(data)
end

Example: Strict Production Code

@strict true

record Config
  api_key: String where length(api_key) > 0
  timeout_ms: Int where timeout_ms > 0
end

cell load_config() -> result[Config, String]
  # All types checked
  # All effects declared
end

Effect Provenance

Strict mode includes cause in error messages:

Error: UndeclaredEffect {http}
  at: cell b() in main.lm.md:10
  cause: call to fetch() in main.lm.md:5
  chain: b() -> a() -> fetch()

Best Practices

1. Keep strict mode on — Catch errors early
2. Only relax for docs — Documentation snippets
3. Declare all effects — Make side effects visible
4. Fix warnings — Don't ignore type issues