Expressions and operators

Expressions and operators

Expressions appear in defaults, fixtures, contract conditions, helper bodies and examples. They describe values, calls and conditions; the compiler checks their meaning without executing the application.

Operator precedence

From strongest to weakest:

Operators	Meaning
(...), member ., call (...)	Grouping, field/member selection, invocation
Unary +, -, not	Numeric sign or Boolean negation
*, /, %	Numeric multiplication, division, remainder
+, -	Numeric addition/subtraction
==, !=, <, <=, >, >=	Comparison
and	Boolean conjunction
or	Boolean disjunction

Arithmetic is numeric; + does not concatenate Text. and, or and not need Boolean values. Comparisons cannot be chained: write a < b and b < c, not a < b < c.

main.expec

examples {
  example "precedence": 2 + 3 * 4 => 14
  example "grouping": (2 + 3) * 4 => 20
  example "remainder": 9 % 4 => 1
  example "Boolean condition": not false and 2 < 3 or false => true
}

These are authored expected outcomes, not compiler evaluation results.

Calls and field access

main.expec

type Book {
  title: Text
}
function titleOf(book: Book) returns Text
examples {
  fixture dune: Book = Book { title: "Dune" }
  example "read the field": dune.title => "Dune"
  example "call a function": titleOf(dune) => "Dune"
}

A selected field must exist on the receiver's known type. A capability called through a receiver must be public. An opaque or optional receiver cannot silently provide a nonoptional field or operation. A named operation is not a call until you supply parentheses.

Collections and records

main.expec

type Book {
  title: Text
}
type Shelf {
  books: List<Book>
  corner: [Number, Number]
}
examples {
  fixture empty: Shelf = Shelf {
    books: [],
    corner: [0, 0],
  }
}

An empty list needs a known expected element type, as books supplies here. An anonymous record needs a suitable unambiguous expected record type. Named record literals distinguish nominal types with otherwise identical fields.

Symbols with other jobs

Symbol	Use
:	Annotate a parameter, field or fixture; separate a record entry; separate a short example's title
=	Alias definition, default, fixture/local value, or scenario capture
=>	Separate a short example's actual expression from its expectation
->	Send an authored interaction message, not a general expression
?	Optional type suffix
|	Type union; Boolean alternatives use or
<T>	Generic parameters or arguments in type contexts

There is no general assignment, indexing operator, lambda, conditional statement or loop syntax in this language version. Runtime implementation belongs in the connected project.

Related: Types · Capabilities and contracts · Examples and scenarios