let*

Type:	-	special form (fsubr)
Source:	-	xlcont.c

Syntax

(let* ([binding ... ]) expr ... )

binding - a variable binding which is one of the forms:

symbol
(symbol init-expr)

symbol - a symbol
init-expr - an initialization expression for symbol

expr - an expression
returns - the value of the last expression

Description

The 'let*' special form is basically a local block construct that contains symbols [with optional initializations] and a block of code [expressions] to evaluate. The first form after the 'let*' is the 'binding' form. It contains a series of 'symbols' or 'bindings'. The 'binding' is a 'symbol' followed by an initialization expression 'init-expr'. If there is no 'init-expr', the 'symbol' will be initialized to NIL. The execution of the bindings will occur from the first to the last binding. The 'let*' form will go through and create and initialize the symbols and then sequentially execute the 'exprs'. The value of the last 'expr' evaluated is returned. When the 'let*' is finished execution, the 'symbols' that were defined will no longer exist or retain their values.

Examples

(let* (x y z)                     ; LET* with local vars
  (print x) (print y) (print z))  ;   prints   NIL NIL NIL

(let* ((a 1) (b 2) (c 3))         ; LET* with local vars & init
  (print (+ a b c)))              ;   prints and returns 6

(let* ((a 1) (b 2) (c (+ a b)))   ; LET* with local vars & init
  (print (+ a b c)))              ;   prints and returns 6

Note:

(let* (a b) ... )

can be understood as:

(let (a)
  (let (b)
    ... ))

See the let* special form in the XLISP 2.0 manual.

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