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Bug #878

RingElem applied to a symbol (repr as a string)

Added by John Abbott almost 8 years ago. Updated almost 7 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Anna Maria Bigatti
Category:
enhancing/improving
Target version:
CoCoA-5.2.0 spring 2017
Start date:
09 May 2016
Due date:
% Done:

100%

Estimated time:
1.80 h
Spent time:
1.35 h

Description

The current design for converting a symbol (repr as a string) into a RINGELEM is inconvenient.

I wanted to do this while demo-ing CoCoA-5 and ended up being rather confused.

The function RingElem works only for symbols without indices; if there are indices then they must be specified using a rather unnatural and awkward syntax e.g. RingElem(P, ["a", 2]) to get a[2].

The call RingElem(P,"a[2]") produces the unhelpful/misleading error "illegal symbol head".

In contrast, the function ReadExpr(P, "a[2]") does work.

Related issues

Related to CoCoA-5 - Feature #606: Evaluate in ring operator (was called :: in CoCoA-4)Closed2014-03-19

Related to CoCoA-5 - Design #1051: ReadExpr(P, string) and RingElem(P, string)Closed2017-04-24

History

#1 Updated by John Abbott almost 8 years ago

Personally I find the situation described quite confusing.

It is not clear to me why ReadExpr is not already included in RingElem.

#2 Updated by John Abbott almost 8 years ago

  • Related to Feature #606: Evaluate in ring operator (was called :: in CoCoA-4) added

#3 Updated by John Abbott almost 7 years ago

  • Related to Design #1051: ReadExpr(P, string) and RingElem(P, string) added

#4 Updated by Anna Maria Bigatti almost 7 years ago

  • Assignee set to Anna Maria Bigatti
  • Target version changed from CoCoA-5.?.? to CoCoA-5.2.0 spring 2017
  • % Done changed from 0 to 90

Fixed, now calls ReadExpr.
Documented.
I kept the syntax RingElem(P, ["a", i]) because it allows variable indices.
Not sure how useful this really is, but it works.

#5 Updated by John Abbott almost 7 years ago

  • Status changed from New to Resolved
  • Estimated time set to 1.80 h

As already indicated in the description, I do not much like the awkward syntax RingElem(P, ["a",i]).

I do see the potential utility of being able to specify the indices as values of variables, and surely RingElem(P, "a["+sprint(i)+"]") is even worse than the "awkward syntax".

What about RingElem(P, "a", [i])? Or we could even do RingElem(P, symbol("a",i)) where symbol in CoCoA-5 could just return the string "a[" + sprint(i) + "]"

Or should we just wait until the function is really needed? The sprint solution can be used by anyone...

#6 Updated by Anna Maria Bigatti almost 7 years ago

John Abbott wrote:

Or should we just wait until the function is really needed? The sprint solution can be used by anyone...

I do not think it is of any use, now that we can use sprint.
And I think it's NOT worth thinking about it.
But I do not feel like gratuituosly remove it or change it.

#7 Updated by Anna Maria Bigatti almost 7 years ago

  • Status changed from Resolved to Closed
  • % Done changed from 90 to 100

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