letrec bug

2008-10-28 Thread Bill Schottstaedt 
I believe this shows a bug in letrec:

guile (let ((x 1)) (let ((x 32) (y x)) y))
1
guile (let ((x 1)) (letrec ((x 32) (y x)) y))

Backtrace:
In standard input:
   2: 0* (let* ((x 1)) (letrec ((x 32) (y x)) y))
   2: 1  (letrec ((x 32) (y x)) y)

standard input:2:14: In expression (letrec (# #) y):
standard input:2:14: Variable used before given a value: x
ABORT: (unbound-variable)

Re: letrec bug

2008-10-28 Thread Mikael Djurfeldt 
2008/10/28 Mikael Djurfeldt [EMAIL PROTECTED]:
 2008/10/28 Mikael Djurfeldt [EMAIL PROTECTED]:
 2008/10/28 Bill Schottstaedt [EMAIL PROTECTED]:
 I believe this shows a bug in letrec:

 guile (let ((x 1)) (let ((x 32) (y x)) y))
 1
 guile (let ((x 1)) (letrec ((x 32) (y x)) y))

 Backtrace:
 In standard input:
   2: 0* (let* ((x 1)) (letrec ((x 32) (y x)) y))
   2: 1  (letrec ((x 32) (y x)) y)

 standard input:2:14: In expression (letrec (# #) y):
 standard input:2:14: Variable used before given a value: x
 ABORT: (unbound-variable)

 Nope.

 From R5RS:

 One restriction on `letrec' is very important: it must be possible
 to evaluate each init without assigning or referring to the
 value of any variable.

 Sorry.  I missed the surrounding let.  Yes, it is a bug.

Sorry again (should never easily throw out comments when its about
letrec :).  The binding of x which letrec introduces covers the entire
letrec expression.  This means that it *is* an error to refer to it in
another init.  We should be grateful that Guile detects this, because
such code will likely behave in an implementation dependent, and not
standard conforming, manner.

R5RS again:

The variables are bound to fresh locations holding
 undefined values, the inits are evaluated in the resulting
 environment (in some unspecified order)

Re: letrec bug

2008-10-28 Thread Mikael Djurfeldt 
2008/10/28 Mikael Djurfeldt [EMAIL PROTECTED]:
 2008/10/28 Bill Schottstaedt [EMAIL PROTECTED]:
 I believe this shows a bug in letrec:

 guile (let ((x 1)) (let ((x 32) (y x)) y))
 1
 guile (let ((x 1)) (letrec ((x 32) (y x)) y))

 Backtrace:
 In standard input:
   2: 0* (let* ((x 1)) (letrec ((x 32) (y x)) y))
   2: 1  (letrec ((x 32) (y x)) y)

 standard input:2:14: In expression (letrec (# #) y):
 standard input:2:14: Variable used before given a value: x
 ABORT: (unbound-variable)

 Nope.

 From R5RS:

 One restriction on `letrec' is very important: it must be possible
 to evaluate each init without assigning or referring to the
 value of any variable.

Sorry.  I missed the surrounding let.  Yes, it is a bug.

Re: letrec bug

2008-10-28 Thread Mikael Djurfeldt 
2008/10/28 Bill Schottstaedt [EMAIL PROTECTED]:
 I believe this shows a bug in letrec:

 guile (let ((x 1)) (let ((x 32) (y x)) y))
 1
 guile (let ((x 1)) (letrec ((x 32) (y x)) y))

 Backtrace:
 In standard input:
   2: 0* (let* ((x 1)) (letrec ((x 32) (y x)) y))
   2: 1  (letrec ((x 32) (y x)) y)

 standard input:2:14: In expression (letrec (# #) y):
 standard input:2:14: Variable used before given a value: x
 ABORT: (unbound-variable)

Nope.

From R5RS:

One restriction on `letrec' is very important: it must be possible
to evaluate each init without assigning or referring to the
value of any variable.

Re: letrec bug

2008-10-28 Thread Bill Schottstaedt 
I read those same paragraphs and interpreted them differently,
but now I agree with you.