//! Parsing rules for scalar path-parameter expressions.
//! The public Rule enum is generated from this grammar; callers normally use
//! eval_expression_with rather than inspecting parser rules directly.
//! Its generated all_rules() method returns a borrowed static slice of the
//! grammar's declared rules in definition order, excluding the built-in EOI
//! (end-of-input) rule. It does not parse or evaluate an expression.
/// Insignificant spaces, tabs, and line breaks between expression tokens.
WHITESPACE = _{ " " | "\t" | "\r" | "\n" }
/// A complete expression with no unconsumed leading or trailing tokens.
complete_expression = { SOI ~ expression ~ EOI }
/// Top-level arithmetic expression.
expression = { sum }
/// Left-associative addition and subtraction of products.
sum = { product ~ (add_op ~ product)* }
/// Addition or subtraction operator.
add_op = { "+" | "-" }
/// Left-associative multiplication and division of powers.
product = { power ~ (mul_op ~ power)* }
/// Multiplication or division operator.
mul_op = { "*" | "/" }
/// Right-associative exponentiation; unary signs bind before the power operator.
power = { unary ~ (pow_op ~ power)? }
/// Exponentiation operator; this grammar uses ^ rather than **.
pow_op = { "^" }
/// Zero or more unary signs applied to a primary expression.
unary = { sign* ~ primary }
/// Unary plus or minus.
sign = { "+" | "-" }
/// Function, constant, variable, number, or parenthesized expression.
primary = { function_call | constant | identifier | number | "(" ~ expression ~ ")" }
/// Named function with a comma-separated argument list; arity is checked on evaluation.
function_call = { identifier ~ "(" ~ expr_list? ~ ")" }
/// One or more function-argument expressions in input order.
expr_list = { expression ~ ("," ~ expression)* }
/// Built-in dimensionless constants pi and e, recognized as complete tokens.
constant = @{ ("pi" | "e") ~ !(ASCII_ALPHANUMERIC | "_") }
/// ASCII variable/function name beginning with a letter or underscore.
identifier = @{ (ASCII_ALPHA | "_") ~ (ASCII_ALPHANUMERIC | "_")* }
/// Unsigned decimal or scientific-notation literal; unary signs are parsed separately.
number = @{ (ASCII_DIGIT+ ~ ("." ~ ASCII_DIGIT*)? | "." ~ ASCII_DIGIT+) ~ (("e" | "E") ~ ("+" | "-")? ~ ASCII_DIGIT+)? }