CoCoA » CoCoA-5

Presumably the list syntax should be the same as what CoCoA prints: ","-separated entries inside square brackets [].
An empty list is allowed.

Ange has a workaround: she has changed the input so that it is simply a succession of polynomials (one per line), with a zero polynomial to mark the end of the list.

I admit I would have found this useful in a number of occasions.
I had followed the same workaround as Ange...

After lunch (rather disappointing fish-and-chips in the mensa), I now think that trying to impose a "list syntax" is not a good idea. The main reason is that we must write a parser (how?), and we must handle syntax errors (tedious).

It should be easy to write a function for reading a list, perhaps something like this:

define ReadListOfRingElem(Istream, R, EndMarker)
  ans := [];
  repeat
    str := GetLine(Istream);
    if str = EndMarker then return ans; endif;
    append(ref ans, RingElem(R, str));
  endrepeat;
enddefine;

Maybe we could make the string "00" a default end marker? Does it even make sense to have a default?

At the moment, input is only via GetLine, which naturally reads a whole line as a string.

Currently we cannot easily handle the case where a single ringlem is spread over several lines, or if there are several ringelems in one line.
Consider these examples:
How many ringelems are here?

x+y
-z

How many ringelems are here?

x -y -z

• KISS the ringelems must be written exactly one per line (effectively "newline" functions as "semicolon")
• the advantage of ReadExprSemicolon is that lines and ringelems are essentially independent (one ringelem may span several lines, and one line may contain (parts of) several ringelems)
• if we do choose to use ReadExprSemicolon, I would suggest changing its name and allowing the user to specify what terminating character to expect (with some restrictons, probably)

For the moment called (also in CoCoA) ReadExprVector(ring, string).
Example ReadExprVector(R, "x-1, y^3-2, x*z")
Think of a good name fast!

reminder: choose name and write doc for cocoa-5

One "advantage" of BlaBlaVector and BlaBlaList is that it help reminds the programmer that indices in the first case start from 0, and in the second case start from 1. Of course, the parts of code which much be changed to get the indices right are almost certainly not the lines in which BlaBlaVector appears... :-/

It could also be that the interface in C++ is a bit different. For example, it may be more convenient in C++ to read a succession of values from a stringstream rather than read them all in one go into a vector (not too sure about this, but it should be considered).

As discussed in #1931, there are now two functions:
(A) RingElems(RING, STRING) example RingElems(P, "x*y,z")
and
(B) RingElemList(RING, STRING) example RingElems(P, "[x*y,z]")

I prefer (A) and it is also implemented in cocoalib.
Not yet documented (neither)

documented