You can declare a variable using a ! form. This takes a variable name, and an expression. It declares a new variable with the given name, and gives it the value of the expression: expression to the variable.

#|kawa:1|# (! binary-kilo 1024)
#|kawa:2|# (! binary-mega (* binary-kilo binary-kilo))
#|kawa:3|# binary-mega
1048576

If you prefer, you can use define instead of !:

#|kawa:1|# (define binary-kilo 1024)
#|kawa:2|# (define binary-mega (* binary-kilo binary-kilo))
#|kawa:3|# binary-mega
1048576

The advantage of using define is that it is portable to other Scheme implementations. The advantages of using ! is that it is shorter; it generalizes to patterns (see later); and it guards against accidentally “shadowing” a variable by a nested variable with the same name.

A ! (or define) typed into the command-line defines a top-level variable.

You can also declare local variables. NEED EXAMPLES.

Alternative forms for defining local variables are let, let*, or letrec/letrec*.