Compare do and do*; they are analogous to let and let*.

On Wednesday, January 22, 2003, at 12:26 PM, feilong wrote:

> Hallo friends,
> Why does not this do expression run?
> 1    (do ((x 1 (+ x 1))
> 2             (y x x))
> 3           ((> x 5))
> 4          (format t "(~A ~A) " x y))
> Error: Attempt to take the value of the unbound variable `X'.
> [condition type: UNBOUND-VARIABLE]
>
> I think that the variable y in row 2 can refer to the variable x. In 
> the first iteration has x been intialised to 1, while do is parallel 
> evaluation, that menas, y can refer to x and assign y to 1. Why does 
> intepreter give wrong report.
>
> why does this do expression run?
> (let ((x 'a))
>         (do ((x 1 (+ x 1))
>             (y x x))
>           ((> x 5))
>          (format t "(~A ~A) " x y))
> (1 A)
> (2 1)
> (3 2)
> (4 3)
> (5 4)
> NIL
>
> I have only added a "let" expression and in "let" initialised x with 
> 'a. In previous "do" expression I have also initialised x with value 
> 1. Whether can not  y direkt refer to x without "let" to initialise x 
> in outmost enviroment?   What difference is there in this "do" 
> expression with "let" and previous "do" expression without "let"?
>
> Best Greetings
> Xu
>
>
-- 
Gary Warren King, Senior Research Fellow, EKSL

Callused men in business suits speak computerese
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