Re: [O] Literate Programming - Continue a Source Block?

[Achim Gratz]

Eric Schulte <address@hidden> writes:
> I think "append" is just as clear as concatenate,

Fair enough, in my mind "append" needs an existing entity, but I guess
it could be an empty one.

> and collate implies shuffling which is not happening.

Well, I was getting ahead of myself...  I hope you don't mind me harping
on about this.

> I'm wary of adding too much duplicate functionality.  It is already
> possible to organize the tangling of many named code blocks using noweb
> reference expansion (a feature which I've used myself on real projects
> in the past).  This existing method allows for unique block names and
> for arbitrary tangling order.

The examples presented in this thread pointed out one difficulty with
how noweb references currently work, namely that you need to know in
advance all block names for finally tangling them and that when adding
or removing things you need to remember to keep these references current
in potentially many places.

> Simplicity is the only reason that the new name-based appending behavior
> was implemented, simplicity which (in my opinion) is lost when the user
> defines a naming and sorting schema.

My general objection is that since you now require that the names be all
the same, there is no way to distinguish between those blocks anymore.
This will come back to bite you when you then later need to make a
distinction since you'll then have to rework everything to unique names
again.  I consider that sort of simplicity a trap for the unwary.

Splitting between a basename and an index extension would instead allow
for appending with the basename and still getting at individual blocks
using the full name (with the index part).  I've had one specific
use-case in mind where this would be needed.  You'd normally just
concatenate all source blocks (let's assume for the moment that the
index part is separated from the basename by "::")

  <<source::*>>

Let's say you have three source blocks and need to point-patch the
second one for this run:

  <<source::1>>
  <<source-patch::2>>
  <<source::3>>

If the three source blocks are all just named "source", there's no way
to do this short of changing their names and all the references that use
them.

The index part doesn't have to be numeric, it just needs to be
orderable.  Anyone not using index extensions gets an implicit one by
order of appearance, so that wouldn't require any code duplication and
you can in this case still say

  <<source>>

Being able to provide custom naming and sorting schemes could be
deferred to hook functions the user has to provide, as they will indeed
be rarely needed.  So an implementation that keeps current behaviour
would provide an implicit indexer (by order of appearance), an empty
sorter and three selectors (all=append, first last).  Anyone who needs
more than that has to customize those functions, but I suppose the more
common application scenarios will sneak into the baseline sooner or
later.  The move from implicit to explicit indexing should be supported
by providing another hook in the implicit indexer.


Regards,
Achim.
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