The expression can be formed as a sequence of assignment expressions followed by one resulting expression. Multiple expressions are delimited by a semicolon (;). An assignment expression has the following syntax:

variable := expression 

The first occurrence of a variable on the left-hand side defines this variable and its type. A reference to a variable in an expression is valid only after its definition. Each following occurrence of a variable, including an occurrence on the left-hand side of the assignment expression, must conform to the variable type.

Example:

a := 2;
b := 4 - a;
3 * b