Block Expressions

Syntax

<block-expr> ::= {
      <stmt> ^*
      <expr> ^?
}

A block expression is a control flow construct for sequencing multiple statements with an optional final expression. A block also introduces a new lexical scope where variable declarations are visible only from after the let statement that declares it until the end of the block.

Each statement is executed sequentially and the type of the entire block is the type of the final expression, or () if the expression is omitted.

Note how the differentiating factor between an expression statement and an expression is the trailing semicolon.

let x: int = { 5 };

let x: () = { 5; };