[ANSI-Smalltalk] #peekFor:

[John O'Keefe]

I suspect that rather than ignoring the standard when implementing
#peekFor:, most/all Smalltalk implementations already had #peekFor:
implemented.  Just to add to the list, the VA Smalltalk #peekFor:
implementation (from 6/6/96 or earlier) also advances the stream when
answering true.

Could this not be considered a documentation oversight that is a candidate
for the Errata STEP?  Oh, what Errata STEP?  Bad me -- I'm the one who was
supposed to create that STEP.

John O'Keefe [|], Principal Smalltalk Architect, Instantiations Inc.


On Wed, Oct 1, 2008 at 2:42 AM, Damien Cassou <damien.cassou at gmail.com>wrote:

> I noticed that too when doing Nile. It seems all implementations
> decided to implement #peekFor: the same way, ignoring the standard. I
> think the standard behavior is useless here because it is equivalent
> to "stream peek = anObject" which is clearer that way.
>
> On Wed, Oct 1, 2008 at 3:35 AM, Richard O'Keefe <ok at cs.otago.ac.nz> wrote:
> > In the Smalltalk standard, we read
> >
> > 5.9.2.8 Message: peekFor: anObject
> >  Synopsis
> >    Peeks at the next object in the stream
> >    and returns true if it matches the argument,
> >    and false if not.
> >  Definition: <gettableStream>
> >    Returns the result of sending #= to the first object
> >    in the receiver's future sequence values with anObject
> >    as the argument.  Returns false if the receiver has
> >    no future sequence values.
> >  Parameters
> >    anObject <Object> uncaptured
> >  Return Value
> >    <boolean> unspecified
> >  Errors
> >    none
> >
> > There is no faintest suggestion here that the state of the
> > stream changes in any way.  In particular, there is no
> > suggestion that a successful match will result in the stream
> > being advanced.
> >
> > However, the Blue Book says on page 199
> >
> >        Determine the response to the message [#]peek.
> >        If it is the same as the argument, anObject,
> >        THEN INCREMENT THE POSITION REFERENCE and
> >        answer true.  Otherwise answer false and do
> >        not change the position reference.
> >
> > The comment in VisualWorks says
> >
> >        Answer false and do not move the position
> >        if self next ~= anObject or if the receiver
> >        is at the end.  Answer true and
> >        INCREMENT POSITION if self next = anObject.
> >
> > The comment in Squeak says
> >
> >        Answer false and do not move over the next element
> >        if it is not equal to the argument, anObject, or
> >        if the receiver is at the end.  Answer true and
> >        INCREMENT THE POSITION for accessing elements,
> >        if the next element is equal to anObject.
> >
> > When I wrote my stream classes, I took the standard text literally,
> > and my #peekFor: never advanced the stream position.  Whoops!
> > I propose the following replacement for the definition:
> >
> >  Definition: <gettableStream>
> >    If the receiver has no future sequence values,
> >    returns false.  Otherwise, determines the result of
> >    sending #= to the first object in the receiver's
> >    future sequence values with anObject as the argument.
> >    If that is false, return false with no change to the
> >    receiver's state.  If #= answers true, the first
> >    object is removed from the receiver's future sequence
> >    values and appended to the end of the receiver's past
> >    sequence values, then true is returned.
> >
> >
> >
> >
> >
> > _______________________________________________
> > ANSI-Smalltalk mailing list
> > ANSI-Smalltalk at lists.openskills.org
> > http://lists.openskills.org/cgi-bin/mailman/listinfo/ansi-smalltalk
> >
>
>
>
> --
> Damien Cassou
> Peter von der Ahé: «I'm beginning to see why Gilad wished us good
> luck». (http://blogs.sun.com/ahe/entry/override_snafu)
>
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>
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