Expressions

An expression is some combination of values, operators, and functions which describes a value (turning an expression into a value is called evaluation).

Examples of expressions in Disco include:

• 5 (a single number, string, boolean, variable, etc. by itself is an expression)
• 1 + 2 (two or more expressions combined by operators is again an expression)
• f(x,3) * g(2) (function calls are expressions)

Examples of things which are not expressions include:

• x : N (this is a type signature, not an expression; it does not have a value, it says what the type of x is)
• x = 3 (this is a definition)

Warning

Be careful not to confuse x = 3 (a definition of the variable x) with x == 3 (a comparison expression which has a value of either true or false depending on whether x is equal to 3 or not). See Definition versus equality testing.