Operators

Operators are special symbols or keywords that take a left and right operand, returning some sort of result.

Comparison

The following comparison operators are supported:

• <= - Less than or equal to
• < - Less than
• > - Greater than
• >= - Greater than or equal to

Both operands must be singular, the table below shows the valid types and their combinations.

	Boolean	String	Integer	Decimal	Date	DateTime	Time	Quantity
Boolean	true	false	false	false	false	false	false	false
String	false	true	false	false	false	false	false	false
Integer	false	false	true	true	false	false	false	false
Decimal	false	false	true	true	false	false	false	false
Date	false	false	false	false	true	true	false	false
DateTime	false	false	false	false	true	true	false	false
Time	false	false	false	false	false	false	true	false
Quantity	false	false	false	false	false	false	false	true*

If one or both of the operands is an empty collection, the operator will return an empty collection.

String ordering is strictly lexical and is based on the Unicode value of the individual characters.

All comparison operators return a Boolean value.

caution

The comparability of units within Quantities is defined within UCUM. You can use the NLM Converter Tool to check whether your units are comparable to each other.

See also: Comparison

Equality

The = operator returns true if the left operand is equal to the right operand, and a false otherwise. The != is the inverse of the = operator.

Both operands must be singular. The valid types and their combinations is the same as for the Comparison operators. In addition to this, Coding types can be compared using the equality operators.

If one or both of the operands is an empty collection, the operator will return an empty collection.

If the operands are Quantity values and are not comparable, an empty collection will be returned.

caution

The comparability of units within Quantities is defined within UCUM. You can use the NLM Converter Tool to check whether your units are comparable to each other.

See also: Equality

Math

The following math operators are supported:

• + - Addition
• - - Subtraction
• * - Multiplication
• / - Division
• mod - Modulus

Math operators support Integer, Decimal and Quantity operands. The modulus operator is not supported for Quantity types.

Both operands must be singular.

If one or both of the operands is an empty collection, the operator will return an empty collection.

Integer and Decimal types can be mixed, while Quantity types can only be used with other Quantity types.

For Integer and Decimal, +, - and * return the same type as the left operand, / returns Decimal and mod returns Integer.

For Quantity types, math operators return a new Quantity with the canonical unit common to both operands. If the units are not comparable, an empty collection is returned.

See also: Math

Date/time arithmetic

The following operators are supported for date arithmetic:

• + - Add a duration to a Date or DateTime
• - - Subtract a duration from a Date or DateTime

Date arithmetic always has a DateTime or Date on the left-hand side, and a duration on the right-hand side. The duration operand is a calendar duration literal. The use of UCUM units is not supported with these operators.

The Date or DateTime operand must be singular. If it is an empty collection, the operator will return an empty collection.

note

The use of arithmetic with the Time type is not supported.

caution

Arithmetic involving instant values is limited to a precision of seconds.

See also: Date/Time Arithmetic

Boolean logic

The following Boolean operations are supported:

• and
• or
• xor - Exclusive OR
• implies - Material implication

Both operands to a Boolean operator must be singular Boolean values.

All Boolean operators return a Boolean value.

See also: Boolean logic

Membership

The following membership operators are supported:

• in ([element] in [collection])
• contains ([collection] contains [element])

If the element operand is a collection with a single item, the operator returns true if the item is in the collection using equality semantics.

If the element is empty, the result is empty. If the collection is empty, the result is false. If the element has multiple items, an error is returned.

See also: Collections

combine

The combine operator merges the left and right operands into a single collection, preserving duplicates. The result is not ordered.

The two operands provided to the combine operator must share the same type.

This implementation has the same semantics as the combine function within the FHIRPath specification, but is implemented as an operator.