3.3.4 Summary of Common Syntax

This subsection lists the most commonly used Scheme syntactic expressions, simply so that you will recognize common special syntax when you see it. For a full description of each of these syntaxes, follow the appropriate reference.

lambda (see Lambda) is used to construct procedure objects.

define (see Top Level) is used to create a new variable and set its initial value.

set! (see Top Level) is used to modify an existing variable’s value.

let, let* and letrec (see Local Bindings) create an inner lexical environment for the evaluation of a sequence of expressions, in which a specified set of local variables is bound to the values of a corresponding set of expressions. For an introduction to environments, see See About Closure.

begin (see begin) executes a sequence of expressions in order and returns the value of the last expression. Note that this is not the same as a procedure which returns its last argument, because the evaluation of a procedure invocation expression does not guarantee to evaluate the arguments in order.

if and cond (see Conditionals) provide conditional evaluation of argument expressions depending on whether one or more conditions evaluate to “true” or “false”.

case (see Conditionals) provides conditional evaluation of argument expressions depending on whether a variable has one of a specified group of values.

and (see and or) executes a sequence of expressions in order until either there are no expressions left, or one of them evaluates to “false”.

or (see and or) executes a sequence of expressions in order until either there are no expressions left, or one of them evaluates to “true”.