20  Looping Constructs

1. loop - basic looping form
2. do - loop while the termination test is NIL
3. do* - 'do' loop with sequential binding
4. dolist - loop through a list
5. dotimes - loop from zero to n-1

(loop expr...) - basic looping form

expr - the body of the loop
returns - never returns (must use non-local exit)

(do (binding...) (texpr rexpr...) expr...)
(do* (binding...) (texpr rexpr...) expr...)

binding - the variable bindings each of which is either:

1) a symbol [which is initialized to NIL]
2) a list of the form: (sym init [step]) where:

sym - is the symbol to bind
init - is the initial value of the symbol
step - is a step expression

texpr - the termination test expression
rexpr - result expressions [the default is NIL]
expr - the body of the loop [treated like an implicit prog]
returns - the value of the last result expression

(dolist (sym expr [rexpr]) expr...) - loop through a list

sym - the symbol to bind to each list element
expr - the list expression
rexpr - the result expression [the default is NIL]
expr - the body of the loop [treated like an implicit prog]

(dotimes (sym expr [rexpr]) expr...) - loop from zero to n-1

sym - the symbol to bind to each value from 0 to n-1
expr - the number of times to loop
rexpr - the result expression [the default is NIL]
expr - the body of the loop [treated like an implicit prog]