21  The Program Feature

1. prog - the program feature
2. prog* - 'prog' with sequential binding
3. block - named block
4. return - cause a prog construct to return a value
5. return-from - return from a named block
6. tagbody - block with labels
7. go - go to a tag within a tagbody or prog
8. progv - dynamically bind symbols
9. prog1 - return the value of the first expression
10. prog2 - return the value of the second expression
11. progn - return the value of the last expression

(prog (binding...) expr...) - the program feature
(prog* (binding...) expr...) - prog with sequential binding

binding - the variable bindings each of which is either:

1) a symbol [which is initialized to NIL]
2) a list whose car is a symbol and whose CADR is an initialization expression

expr - expressions to evaluate or tags [symbols]
returns - NIL or the argument passed to the return function

(block name expr...) - named block

name - the block name [symbol]
expr - the block body
returns - the value of the last expression

(return [expr]) - cause a prog construct to return a value

expr - the value [defaults to NIL]
returns - never returns

(return-from name [value]) - return from a named block

name - the block name [symbol]
value - the value to return [defaults to NIL]
returns - never returns

(tagbody expr...) - block with labels

expr - expression[s] to evaluate or tags [symbols]
returns - NIL

(go sym) - go to a tag within a tagbody or prog

sym - the tag [quoted]
returns - never returns

(progv slist vlist expr...) - dynamically bind symbols

slist - list of symbols
vlist - list of values to bind to the symbols
expr - expression[s] to evaluate
returns - the value of the last expression

(prog1 expr1 expr...) - execute expressions sequentially

expr1 - the first expression to evaluate
expr - the remaining expressions to evaluate
returns - the value of the first expression

(prog2 expr1 expr2 expr...) - execute expressions sequentially

expr1 - the first expression to evaluate
expr2 - the second expression to evaluate
expr - the remaining expressions to evaluate
returns - the value of the second expression

(progn expr...) - execute expressions sequentially

expr - the expressions to evaluate
returns - the value of the last expression [or NIL]