learning scheme : difference in letrec behavior

learning scheme : difference in letrec behavior

[Debabrata Pani]

In kawa (2.1 , 2.0) ,
the expression and its result

#|kawa:27|# (letrec ((x 1) (y (+ x 2))) (+ y x))
4
#|kawa:28|#

But the above expression fails in chicken/gambit
gsi error message
*** ERROR IN (console)@1.19 -- (Argument 1) NUMBER expected
(+ #!unbound 2)

from my point of view , this is harmless. And probably portability
with other scheme implementations is not my concern as well.

But will this have any other unwarranted impact ?

Regards,
Debabrata Pani

Re: learning scheme : difference in letrec behavior

[Per Bothner]

On 11/02/2015 06:42 PM, Debabrata Pani wrote:
> In kawa (2.1 , 2.0) ,
> the expression and its result
>
> #|kawa:27|# (letrec ((x 1) (y (+ x 2))) (+ y x))
> 4
> #|kawa:28|#
>
> But the above expression fails in chicken/gambit
> gsi error message
> *** ERROR IN (console)@1.19 -- (Argument 1) NUMBER expected
> (+ #!unbound 2)
>
> from my point of view , this is harmless. And probably portability
> with other scheme implementations is not my concern as well.

Kawa basically implements 'letrec' as if it were 'letrec*'.
I.e. it evaluates the init expressions in order, while R7RS
makes it unspecified.  This is allowed as an implementation
dependency.

> But will this have any other unwarranted impact ?

Only that you depend on Kawa-specific unportable semantics.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/

Re: learning scheme : difference in letrec behavior

[Per Bothner]

On 11/02/2015 06:52 PM, Per Bothner wrote:

> Kawa basically implements 'letrec' as if it were 'letrec*'.
> I.e. it evaluates the init expressions in order, while R7RS
> makes it unspecified.  This is allowed as an implementation
> dependency.

This is actually covered in the Kawa manual:

http://www.gnu.org/software/kawa/Local-binding-constructs.html
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/

Re: learning scheme : difference in letrec behavior

[Debabrata Pani]

Hi Per,

my bad that I did not refer to the *let* documentation in kawa.

But your explanation regarding R7RS spec was  important for me.

Regards,
Debabrata Pani

On Tue, Nov 3, 2015 at 8:25 AM, Per Bothner <per@bothner.com> wrote:
> On 11/02/2015 06:52 PM, Per Bothner wrote:
>
>> Kawa basically implements 'letrec' as if it were 'letrec*'.
>> I.e. it evaluates the init expressions in order, while R7RS
>> makes it unspecified.  This is allowed as an implementation
>> dependency.
>
>
> This is actually covered in the Kawa manual:
>
> http://www.gnu.org/software/kawa/Local-binding-constructs.html
>
> --
>         --Per Bothner
> per@bothner.com   http://per.bothner.com/