Enum MatchError 

#[non_exhaustive]
pub enum MatchError {
    ProseValueReachable {
        rule: String,
        prose: String,
    },
    UnrepresentableTerminal {
        rule: String,
        terminal: String,
    },
    UnknownRule(String),
    LeftRecursionDetected {
        rule: String,
    },
    StepLimit,
    DepthLimit,
}

Recognition could not be attempted, or could not be finished.

Never returned to mean “the input does not match” — that is Ok(false).

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

ProseValueReachable

The start rule can reach a prose value, which has no matching semantics (SCOPE.md 6.5).

Fields

rule: String

The start rule.

prose: String

The prose text reached.

UnrepresentableTerminal

The start rule can reach a terminal that no Unicode scalar value can match (SCOPE.md 6.1).

Fields

rule: String

The start rule.

terminal: String

The terminal, in canonical spelling.

UnknownRule(String)

No such rule in the grammar or the core environment.

Tuple Fields

0: String

The requested name.

LeftRecursionDetected

The in-progress guard fired. Unreachable after check, which rejects left recursion outright; kept as belt and braces (SCOPE.md 6.2).

Fields

rule: String

The rule the guard fired on.

StepLimit

MatchOptions::max_steps was exceeded. Never a silent reject (D16).

DepthLimit

MatchOptions::max_depth was exceeded.

The recognizer descends recursively, so nesting in the input becomes depth on the call stack. Without this limit a deeply nested input overflows the stack, and a stack overflow aborts the process — it cannot be caught and reported as “could not decide”, which is what every other limit here does.

Trait Implementations

impl Clone for MatchError

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MatchError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for MatchError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for MatchError

impl Error for MatchError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl PartialEq for MatchError

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for MatchError