Expressions

Value expressions

Value expressions are used to compute values. They can be used wherever a value is expected, for example in field initializations, in pattern matching, or in type parametrization.

From this point forward we will omit "value" and just say "expression", implying that it is a value expression, unless otherwise specified.

\[ \begin{align*} expression ::=& \ expression \left(\ \texttt{+} \mid \texttt{-} \mid \texttt{*} \mid \texttt{/} \mid \texttt{&} \mid \texttt{|}\ \right) expression \\ \mid&\ \texttt{-} expression \\ \mid&\ \texttt{!} expression \\ \mid&\ primary \end{align*} \]

Precedence and Associativity

DependoBuf uses the same precedence and associativity rules as any other language, which are also used in mathematics. The following table lists operators in order of decreasing precedence:

Operator	Description
!	Logical NOT
-	Arithmetic negation
*	Multiplication
/	Division
&	Logical AND
+	Addition
-	Subtraction
|	Logical OR

Primary expressions

Primary is like an atomic expression. It can be a value, a variable (with optional field access), or a parenthesized expression.

\[ \begin{align*} var\_access ::=&\ var\_identifier \lbrace \ \texttt{.}\ var\_identifier \rbrace \\ primary ::=&\ value \mid var\_access \mid \texttt{(} expression \texttt{)} \end{align*} \]

Type expressions

Type expressions are used to compute types. They can be used wherever a type is expected: in declarations of parameters (be it type parameters or rpc parameters), or in field declarations. Such a variable declaration is called a typed variable in our grammar. It is simply a variable identifier followed by a type expression.

Type expressions consist of type name and optional type parameters. Type parameters need to be primary expressions to avoid ambiguity.

\[ \begin{align*} type\_expr ::=&\ type\_identifier \lbrace primary \rbrace \\ typed\_variable ::=&\ var\_identifier\ type\_expr \end{align*} \]