Query on using `stream-cons' with srfi-14

Query on using `stream-cons' with srfi-14

[Kumar Appaiah]

Hi.

I'm trying out the SICP examples on streams using kawa. I am currently
stuck on a stream example. The particular blurb of code is:

(define cons-stream stream-cons)
(define the-empty-stream stream-null)
(define (stream-enumerate-interval low high)
  (if (> low high)
      the-empty-stream
      (cons-stream
       low
       (stream-enumerate-interval (+ low 1) high))))

The full code can be found on this page:
https://gist.github.com/kumanna/94cb8bb130fed4805d21

Running this gives me the following error:
Argument  '#<macro stream-cons>' to 'apply-to-args' has wrong type (kawa.lang.Macro) (expected: procedure)
        at gnu.kawa.functions.ApplyToArgs.applyN(ApplyToArgs.java:165)
        at gnu.mapping.ProcedureN.apply3(ProcedureN.java:48)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.streamEnumerateInterval(3-streams-1.scm:89)
        at atInteractiveLevel$21.apply2(3-streams-1.scm:84)
        at gnu.expr.ModuleMethod.apply2(ModuleMethod.java:198)
        at atInteractiveLevel$23.lambda1(3-streams-1.scm:98)
        at atInteractiveLevel$23.apply0(3-streams-1.scm:98)
        at gnu.expr.ModuleBody.applyN(ModuleBody.java:233)
        at gnu.expr.ModuleMethod.applyN(ModuleMethod.java:216)
        at gnu.kawa.functions.ApplyToArgs.applyN(ApplyToArgs.java:137)
        at gnu.mapping.ProcedureN.apply1(ProcedureN.java:31)
        at atInteractiveLevel$8.timeExecute(3-streams-1.scm:45)
        at atInteractiveLevel$8.apply1(3-streams-1.scm:43)
        at gnu.expr.ModuleMethod.apply1(ModuleMethod.java:192)
        at gnu.expr.ModuleMethod.apply(ModuleMethod.java:163)
        at gnu.mapping.CallContext.runUntilDone(CallContext.java:234)
        at gnu.expr.ModuleExp.evalModule2(ModuleExp.java:373)
        at gnu.expr.ModuleExp.evalModule(ModuleExp.java:210)
        at kawa.Shell.run(Shell.java:279)
        at kawa.Shell.runFile(Shell.java:482)
        at kawa.Shell.runFileOrClass(Shell.java:420)
        at kawa.repl.processArgs(repl.java:250)
        at kawa.repl.main(repl.java:850)

What am I doing wrong? Please let me know if I am not being clear.

Thanks.

Kumar
-- 
Kumar Appaiah

Re: Query on using `stream-cons' with srfi-14

[Per Bothner]

On 07/23/2014 04:23 AM, Kumar Appaiah wrote:
> Hi.
>
> I'm trying out the SICP examples on streams using kawa. I am currently
> stuck on a stream example. The particular blurb of code is:
>
> (define cons-stream stream-cons)
> (define the-empty-stream stream-null)
>  ...
> Running this gives me the following error:
> Argument  '#<macro stream-cons>' to 'apply-to-args' has wrong type (kawa.lang.Macro) (expected: procedure)
>          at gnu.kawa.functions.ApplyToArgs.applyN(ApplyToArgs.java:165)

> What am I doing wrong? Please let me know if I am not being clear.

stream-cons is syntax - specifically a macro.
It doesn't work to treat it as a value that is
available at run-time.  (It might be reasonable for Kawa
to warn about this.)

You would need to define cons-stream as a macro, for
example (untested code):

(define-syntax cons-stream
   (syntax-rules ()
     ((_ a b) (stream-cons a b))))
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/

Re: Query on using `stream-cons' with srfi-14

[Jamison Hope]

On Jul 23, 2014, at 1:44 PM, Per Bothner <per@bothner.com> wrote:

> On 07/23/2014 04:23 AM, Kumar Appaiah wrote:
>> Hi.
>> 
>> I'm trying out the SICP examples on streams using kawa. I am currently
>> stuck on a stream example. The particular blurb of code is:
>> 
>> (define cons-stream stream-cons)
>> (define the-empty-stream stream-null)
>> ...
>> Running this gives me the following error:
>> Argument  '#<macro stream-cons>' to 'apply-to-args' has wrong type (kawa.lang.Macro) (expected: procedure)
>>         at gnu.kawa.functions.ApplyToArgs.applyN(ApplyToArgs.java:165)
> 
>> What am I doing wrong? Please let me know if I am not being clear.
> 
> stream-cons is syntax - specifically a macro.
> It doesn't work to treat it as a value that is
> available at run-time.  (It might be reasonable for Kawa
> to warn about this.)
> 
> You would need to define cons-stream as a macro, for
> example (untested code):
> 
> (define-syntax cons-stream
>  (syntax-rules ()
>    ((_ a b) (stream-cons a b))))


It'll also work to define cons-stream as an alias:

(define-alias cons-stream stream-cons)

At least that works at the REPL with a slightly out-of-date
build of Kawa circa r7863 or so.



BTW the streams stuff is in SRFI-41, not SRFI-14.  At first
I was very confused by what the char-set library had to do
with streams working or not working.

--
Jamison Hope
The PTR Group
www.theptrgroup.com

Re: Query on using `stream-cons' with srfi-14

[Kumar Appaiah]

On Wed, Jul 23, 2014 at 02:00:56PM -0400, Jamison Hope wrote:
> > 
> >> What am I doing wrong? Please let me know if I am not being clear.
> > 
> > stream-cons is syntax - specifically a macro.
> > It doesn't work to treat it as a value that is
> > available at run-time.  (It might be reasonable for Kawa
> > to warn about this.)
> > 
> > You would need to define cons-stream as a macro, for
> > example (untested code):
> > 
> > (define-syntax cons-stream
> >  (syntax-rules ()
> >    ((_ a b) (stream-cons a b))))
> 
> 
> It'll also work to define cons-stream as an alias:
> 
> (define-alias cons-stream stream-cons)

Thanks. This works perfectly.

> BTW the streams stuff is in SRFI-41, not SRFI-14.  At first
> I was very confused by what the char-set library had to do
> with streams working or not working.

Sorry. This was an idiotic typo; the code actually "requires"
srfi-41. Sorry!

Kumar
-- 
Kumar Appaiah

Re: Query on using `stream-cons' with srfi-14

[Kumar Appaiah]

On Wed, Jul 23, 2014 at 10:44:51AM -0700, Per Bothner wrote:
> 
> 
> On 07/23/2014 04:23 AM, Kumar Appaiah wrote:
> >Hi.
> >
> >I'm trying out the SICP examples on streams using kawa. I am currently
> >stuck on a stream example. The particular blurb of code is:
> >
> >(define cons-stream stream-cons)
> >(define the-empty-stream stream-null)
> > ...
> >Running this gives me the following error:
> >Argument  '#<macro stream-cons>' to 'apply-to-args' has wrong type (kawa.lang.Macro) (expected: procedure)
> >         at gnu.kawa.functions.ApplyToArgs.applyN(ApplyToArgs.java:165)
> 
> >What am I doing wrong? Please let me know if I am not being clear.
> 
> stream-cons is syntax - specifically a macro.
> It doesn't work to treat it as a value that is
> available at run-time.  (It might be reasonable for Kawa
> to warn about this.)
> 
> You would need to define cons-stream as a macro, for
> example (untested code):
> 
> (define-syntax cons-stream
>   (syntax-rules ()
>     ((_ a b) (stream-cons a b))))

Indeed, this works well. I was not acquainted with define-syntax and
friends, so thank you for the explanation.

Kumar
-- 
Kumar Appaiah