# Terminology

Some terminology will be useful. It is perhaps best to read this section only briefly, and to refer back to it when necessary. The term *expression* will be used to refer to a textual entity. The term *value* will be used to refer to a run-time value denoted by an expression. To understand the difference between an expression and a value consider the expressions `1+2` and `3`. The expressions are textually different but they denote the same value, namely the integer 3. A *function expression* is any expression of the form `function ... end function` or of the form `func< ... | ... >`. The former type of function expression will be said to be *in the statement form*, the latter *in the expression form*. A *function value* is the run-time value denoted by a function expression. As with integers, two function expressions can be textually different while denoting the same (i.e., extensionally equal) function value. To clearly distinguish function values from function expressions, the notation FUNC( … : … ) will be used to describe function *values*. The *formal arguments* of a function in the statement form are the identifiers that appear between the brackets just after the `function` keyword, while for a function in the expression form they are the identifiers that appear before the `|`. The *arguments* to a function are the expressions between the brackets when a function is applied. The *body* of a function in the statement form is the statements after the formal arguments. The body of a function in the expression form is the expression after the `|` symbol. An identifier is said to occur *inside* a function expression when it is occurs textually anywhere in the body of a function.