cons* and append!

cons* and append!

[Brian S McQueen]

I few weeks back I asked abit about list building and I got some helpful
responses.  The operator cons* was recommended to me.  Well I noticed
append! yesterday.  Does anyone have any comments on this?  It seems an
excellent way of extending proper lists without copying or reallocating
elements, since it merely clobbers the trailing null list of one list and
inserts the car of the appended list in its place.  Are there some hidden
expenses I am unaware of?  Does it have to walk the entire length of the
first list to find the end?

I will look at the source code.  I should've looked at it before I wrote
this, but comments would still be appreciated!

Brian


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Re: cons* and append!

[Andreas Rottmann]

Brian S McQueen <bqueen@nas.nasa.gov> writes:

> I few weeks back I asked abit about list building and I got some helpful
> responses.  The operator cons* was recommended to me.  Well I noticed
> append! yesterday.  Does anyone have any comments on this?  It seems an
> excellent way of extending proper lists without copying or reallocating
> elements, since it merely clobbers the trailing null list of one list and
> inserts the car of the appended list in its place.  Are there some hidden
> expenses I am unaware of?  Does it have to walk the entire length of the
> first list to find the end?
>
Yes, append! will have to walk all the lists but the last. All you
save is copying them.

Andy
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Re: cons* and append!

[Stephen Compall]

Brian S McQueen <bqueen@nas.nasa.gov> writes:

> I few weeks back I asked abit about list building and I got some
> helpful responses.  The operator cons* was recommended to me.  Well
> I noticed append! yesterday.  Does anyone have any comments on this?
> It seems an excellent way of extending proper lists without copying
> or reallocating elements, since it merely clobbers the trailing null
> list of one list and inserts the car of the appended list in its
> place.  Are there some hidden expenses I am unaware of?  Does it
> have to walk the entire length of the first list to find the end?

Yes, it does.  This is why we have (ice-9 q) instead of just appending
new cells to the end.

--
Stephen Compall or s11 or sirian

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with as you will.
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