#3 special form "do" syntax error

[Bill Hale]

If the <expression> is omitted from the "test"
clause of the "do" form, where you have
(<test> <expression> ...), then you get a
syntax error.

For example:

(do ((i 0 (+ i 1))) ((= i 5) ) (display (* i i)))

Here the exit test clause ((= i 5) ) has no
<expression> provided.

Below are the relevant data to test the bug and
a suggested change for the "do" special form.

Remarks: 1) first "do" works;
2) second "do" gets syntax error
3) first "define do" is present code
4) second "define do" is a suggested
change of using "cond" rather than "if"

Note: I am not at all sure that the second "define
do" is correct or not.

============================================

(do ((i 0 (+ i 1))) ((= i 5) 1000) (display (* i i)))

(do ((i 0 (+ i 1))) ((= i 5) ) (display (* i i)))

(define do
(macro (bindings test-and-result . body)
(let ((variables (map first bindings))
(inits (map second bindings))
(steps (map (lambda (clause)
(if (null? (cddr clause))
(first clause)
(third clause)))
bindings)))
`(letrec (([loop]
(lambda ,variables
(if ,(first test-and-result)
(begin . ,(rest test-and-result))
(begin
,@body
([loop] . ,steps))))))
([loop] . ,inits)))))

(define do
(macro (bindings test-and-result . body)
(let ((variables (map first bindings))
(inits (map second bindings))
(steps (map (lambda (clause)
(if (null? (cddr clause))
(first clause)
(third clause)))
bindings)))
`(letrec (([loop]
(lambda ,variables
(cond
(,(first test-and-result)
. ,(rest test-and-result))
(else (begin
,@body
([loop] . ,steps)))))))
([loop] . ,inits)))))

============================================

This problem arose when I was trying to install
the "slib" library.

-- Bill Hale

[Timothy John Hickey]

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This has been fixed in the current version (5.0)