Enum Expression 

pub enum Expression {
    Term(Term),
    Invocation(Box<Expression>, Invocation),
    Indexer(Box<Expression>, Box<Expression>),
    Polarity(char, Box<Expression>),
    Multiplicative(Box<Expression>, String, Box<Expression>),
    Additive(Box<Expression>, String, Box<Expression>),
    Type(Box<Expression>, String, TypeSpecifier),
    Union(Box<Expression>, Box<Expression>),
    Inequality(Box<Expression>, String, Box<Expression>),
    Equality(Box<Expression>, String, Box<Expression>),
    Membership(Box<Expression>, String, Box<Expression>),
    And(Box<Expression>, Box<Expression>),
    Or(Box<Expression>, String, Box<Expression>),
    Implies(Box<Expression>, Box<Expression>),
    Lambda(Option<String>, Box<Expression>),
    InstanceSelector(String, Vec<(String, Box<Expression>)>),
}

Represents a FHIRPath expression

This enum represents the different kinds of expressions that can appear in a FHIRPath expression tree. It forms the core of the abstract syntax tree (AST) produced by the parser. Each variant corresponds to a different type of expression in the FHIRPath language, including basic terms, operators, and function invocations.

The Expression tree is built during parsing and later evaluated by the evaluator to produce a result value. The structure preserves operator precedence and expression nesting as specified in the FHIRPath grammar.

Variants

Term(Term)

A basic term (literal, invocation, etc.)

Invocation(Box<Expression>, Invocation)

A method or function invocation on an expression (e.g., Patient.name.given.first())

Indexer(Box<Expression>, Box<Expression>)

An indexer expression (e.g., Patient.name[0])

Polarity(char, Box<Expression>)

A unary polarity expression (+ or -) (e.g., -5 or +value)

Multiplicative(Box<Expression>, String, Box<Expression>)

A multiplicative expression (*, /, div, mod) (e.g., value * 2 or amount div 10)

Additive(Box<Expression>, String, Box<Expression>)

An additive expression (+ or -) (e.g., value + 5 or total - tax)

Type(Box<Expression>, String, TypeSpecifier)

A type operation (is, as) (e.g., value is Integer or patient as Patient)

Union(Box<Expression>, Box<Expression>)

A union operation (|) (e.g., Patient.name | Patient.address)

Inequality(Box<Expression>, String, Box<Expression>)

An inequality comparison (<, <=, >, >=) (e.g., value > 5 or date <= today())

Equality(Box<Expression>, String, Box<Expression>)

An equality comparison (=, !=, , !) (e.g., name = 'John' or birthDate ~ @2020)

Membership(Box<Expression>, String, Box<Expression>)

A membership test (in, contains) (e.g., 'John' in Patient.name.given or Patient.name contains 'John')

And(Box<Expression>, Box<Expression>)

A logical AND operation (e.g., value > 5 and value < 10)

Or(Box<Expression>, String, Box<Expression>)

A logical OR or XOR operation (e.g., status = 'active' or status = 'pending')

Implies(Box<Expression>, Box<Expression>)

A logical IMPLIES operation (e.g., exists() implies value > 0)

Lambda(Option<String>, Box<Expression>)

A lambda expression with optional identifier (e.g., item => item.value > 10)

InstanceSelector(String, Vec<(String, Box<Expression>)>)

An instance selector expression (e.g., Quantity { value: 5, unit: 'mg' }) Contains the type name and a list of field name/expression pairs.

Trait Implementations

impl Clone for Expression

fn clone(&self) -> Expression

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Expression

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

Formats the value using the given formatter.

impl PartialEq for Expression

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for Expression