THE PROGRAM FEATURE

(prog (<binding>...) <expr>...)

PROG WITH SEQUENTIAL BINDING

(prog* (<binding>...) <expr>...)

fsubr -- equivalent to (let () (block NIL (tagbody ...)))

<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

NAMED BLOCK

(block <name> <expr>...)

fsubr

<name> the block name (quoted symbol)

<expr> the block body

returns the value of the last expression

CAUSE A PROG CONSTRUCT TO RETURN A VALUE

(return [<expr>])

fsubr

<expr> the value (defaults to NIL)

returns never returns

RETURN FROM A NAMED BLOCK OR FUNCTION

(return-from <name> [<value>])

fsubr. In traditional Xlisp, the names are dynamically scoped. A compilation option (default) uses lexical scoping like Common Lisp.

<name> the block or function name (quoted symbol). If name is NIL, use function RETURN.

<value> the value to return (defaults to NIL)

returns never returns

BLOCK WITH LABELS

(tagbody <expr>...)

fsubr

<expr> expression(s) to evaluate or tags (symbols)

returns NIL

GO TO A TAG WITHIN A TAGBODY

(go <sym>)

fsubr. In traditional Xlisp, tags are dynamically scoped. A compilation option (default) uses lexical scoping like Common Lisp.

<sym> the tag (quoted)

returns never returns

DYNAMICALLY BIND SYMBOLS

(progv <slist> <vlist> <expr>...)

fsubr

<slist> list of symbols (evaluated)

<vlist> list of values to bind to the symbols (evaluated)

<expr> expression(s) to evaluate

returns the value of the last expression

EXECUTE EXPRESSIONS SEQUENTIALLY

(prog1 <expr1> <expr>...)

fsubr

<expr1> the first expression to evaluate

<expr> the remaining expressions to evaluate

returns the value of the first expression

EXECUTE EXPRESSIONS SEQUENTIALLY

(prog2 <expr1> <expr2> <expr>...)

fsubr

<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

EXECUTE EXPRESSIONS SEQUENTIALLY

(progn <expr>...)

fsubr

<expr> the expressions to evaluate

returns the value of the last expression (or NIL)

XLISP-PLUS - Version 2.1g - Tom Almy tom.almy@tek.com - 18 JUL 94

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