Caution
You’re reading a draft of the Ferrocene Language Specification. Some parts of this document might be missing, incomplete or incorrect. Our aim is to have the specification ready by the end of 2022.
8. Statements¶
Syntax
Statement::=ExpressionStatement|Item|LetStatement|TerminatedMacroInvocation| ;
Legality Rules
8:1 An expression statement is an expression whose result is ignored.
8:2 An item statement is a statement that is expressed as an item.
8:3 An empty statement is a statement expressed as character 0x3B (semicolon).
8:4 A macro statement is a statement expressed as a terminated macro invocation.
Dynamic Semantics
8:5 Execution is the process by which a statement achieves its runtime effects.
8:6 The execution of an empty statement has no effect.
8.1. Let Statements¶
Syntax
LetStatement::=OuterAttributeOrDoc* letPatternWithoutAlternationTypeAscription? (=Expression)? ;
Legality Rules
8.1:1 A let statement is a statement that introduces new bindings produced by its pattern-without-alternation.
8.1:2 The type of a variable introduced by a let statement is determined as follows:
8.1:3 If the let statement appears with a type ascription, then the type is the type specified by the type ascription.
8.1:4 If the let statement lacks a type ascription, then the type is inferred using type inference.
8.1:5 The value of a variable introduced by a let statement is determined as follows:
8.1:6 If the let statement appears with an expression, then the value is the value of the expression.
8.1:7 If the let statement lacks an expression, then the variable is uninitialized.
8.1:8 The pattern of a let statement shall be irrefutable.
Dynamic Semantics
8.1:9 The execution of a let statement proceeds as follows:
8.1:10 If the let statement appears with an expression, then:
8.1:11 The expression is evaluated.
8.1:12 The value of the expression is assigned to each variable introduced by the let statement.
Examples
let local = 0;
let local: u32;
let (a, b) = (0, 0);
8.2. Expression Statements¶
Syntax
ExpressionStatement::=ExpressionWithBlock;? |ExpressionWithoutBlock;
Legality Rules
8.2:1 An expression statement is an expression whose result is ignored.
8.2:2 The expected type of an expression statement without character 0x3B (semicolon) is the unit type.
Dynamic Semantics
8.2:3 The execution of an expression statement proceeds as follows:
Examples
let mut values = vec![1, 2, 3];
8.2:6
The following expression statement ignores the result from pop().
values.pop();
8.2:7 The following expression statement does not require a semicolon.
if values.is_empty() {
values.push(42);
}
else {
values.remove(0);
}
8.2:8 The following expression statement is not an index expression.
[42];