Enum Expr 

pub enum Expr {
    StringEq(String),
    StringEqCI(String),
    RuleRef(String),
    CharOf(String),
    Sequence(Vec<Expr>),
    Alternation(Vec<Expr>),
    Repetition(Box<Expr>),
    Optional(Box<Expr>),
    NotFollowedBy(Box<Expr>),
    SideCondition(Box<Expr>, &'static str),
}

Intermediate representation of a BNF/EBNF expression. All instances are maintained in optimized form.

Variants

StringEq(String)

A case-sensitive literal, formatted as "text".

StringEqCI(String)

A case-insensitive literal, formatted as "text"i.

RuleRef(String)

A reference to another named rule.

CharOf(String)

A character class, formatted as 'label'.

Sequence(Vec<Expr>)

Concatenation: A B C.

Alternation(Vec<Expr>)

Alternation: A | B | C.

Repetition(Box<Expr>)

Zero or more repetitions: { A }.

Optional(Box<Expr>)

Zero or one: [ A ].

NotFollowedBy(Box<Expr>)

Negative lookahead: !A.

SideCondition(Box<Expr>, &'static str)

A side-condition beyond the shown syntax: A ^1 (see Expr::side_conditions).

Implementations

impl Expr

pub fn empty() -> Expr

Matches nothing; omitted from formatted output. Represented as an empty Sequence rather than its own variant, since format_list already renders one as nothing.

pub fn sequence(exprs: Vec<Expr>) -> Expr

Create a sequence, automatically flattening nested sequences.

pub fn alternation(exprs: Vec<Expr>) -> Expr

Create an alternation, automatically flattening.

pub fn repetition(expr: Expr) -> Expr

Create a repetition, dropping any hidden (Empty) elements first; an entirely-hidden inner expression vanishes rather than showing as { }.

pub fn optional(expr: Expr) -> Expr

Create an optional, dropping any hidden (Empty) elements first; an entirely-hidden inner expression vanishes rather than showing as [ ].

pub fn side_condition(expr: Expr, text: &'static str) -> Expr

Attach a side-condition to expr, reported as a numbered marker — see Expr::side_conditions.

pub fn side_conditions(&self) -> Vec<&'static str>

This expression’s SideCondition texts, deduplicated by string equality, in first-occurrence order — the same order format numbers their ^1, ^2, … markers. Callers print these as footnotes after the formatted expression.

pub fn format(&self, f: &mut dyn Write) -> Result

Format this expression as EBNF. Each SideCondition renders as a numbered marker (^1, ^2, …) rather than its text — see side_conditions for the footnotes to print alongside.

Trait Implementations

impl Clone for Expr

fn clone(&self) -> Expr

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Expr

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

Formats the value using the given formatter.

impl Eq for Expr

impl PartialEq for Expr

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Expr