Project

General

Profile

Design #1540

Double power

Added by John Abbott over 3 years ago. Updated over 2 years ago.

Status:
Closed
Priority:
Normal
Assignee:
John Abbott
Category:
enhancing/improving
Target version:
CoCoA-5.4.0
Start date:
16 Nov 2020
Due date:
% Done:

100%

Estimated time:
2.49 h
Spent time:
2.35 h

Description

What do you think CoCoA does with the following input?

x^2^3;

What do you think CoCoA should do with that input?

Related issues

Related to CoCoALib - Design #1538: RingElem from string (ReadExpr)Closed2020-11-13

Related to CoCoALib - Bug #1579: Readexpr/RingElem: unhelpful error message when input is wrongClosed2021-02-23

History

#1 Updated by John Abbott over 3 years ago

I think CoCoA should give a warning or even an error. Currently, it gives neither!
On my computer I got x^8

Since CoCoA warns for something like 2/3*x, I was quite surprised that no warning was given for a "double power".

#2 Updated by John Abbott over 3 years ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 10

If we do look at handling exponents, it might be nice to improve the error mesg when a negative exponent is given without brackets:

/**/ 2^-2;
--> ERROR: Invalid start of expression
--> 2^-2;
-->   ^

It would be more helpful if the message said that negative exponents must be in brackets (or indeed any exponent which is not a non-neg integer literal).

#3 Updated by John Abbott over 3 years ago

  • Related to Design #1538: RingElem from string (ReadExpr) added

#4 Updated by John Abbott over 3 years ago

I would like to maintain reasonable compatibility between the way CoCoA-5 parses expressions and the way RingElem or ReadExpr parses expressions.
In particular, on the whole, if an expression is valid for CoCoA (without warnings/errors) then it should be valid with the same meaning in ReadExpr;
and vice versa.

An significant difference at the moment is that CoCoA-5 allows fairly general expressions as exponents whereas ReadExpr expects just an integer literal
(in brackets if negative).

#5 Updated by John Abbott over 3 years ago

Relevant source is probably in Parser.C around line 1890; Parser::parsePowerExpression

#6 Updated by John Abbott over 3 years ago

  • Target version changed from CoCoA-5.4.0 to CoCoA-5.4.2

#7 Updated by John Abbott about 3 years ago

  • Status changed from In Progress to Resolved
  • Assignee set to John Abbott
  • % Done changed from 10 to 70

I think I have solved the main problem and also the one mentioned in comment 2.
Solution is not elegant, but I do not want to spend more time working with the parser.

Will check in soon.

Current behaviour:

/**/ 2^3^4;
--> WARNING: "^" is right associative; use brackets to avoid this warning
--> 2^3^4;
-->   ^^^
2417851639229258349412352
/**/ 2^+2;
--> ERROR: Exponent may not start with plus or minus; use brackets
--> 2^+2;
-->   ^
/**/ 2^-2;
--> ERROR: Exponent may not start with plus or minus; use brackets
--> 2^-2;
-->   ^

#8 Updated by John Abbott about 3 years ago

  • Related to Bug #1579: Readexpr/RingElem: unhelpful error message when input is wrong added

#9 Updated by John Abbott over 2 years ago

  • Status changed from Resolved to Closed
  • % Done changed from 70 to 100
  • Estimated time set to 2.49 h

#10 Updated by John Abbott over 2 years ago

  • Target version changed from CoCoA-5.4.2 to CoCoA-5.4.0

Also available in: Atom PDF