| Type | Wish | Status | waiting | Date | 20-Jan-2011 23:26 |
|---|---|---|---|---|---|
| Version | alpha 110 | Category | Native | Submitted by | BrianH |
| Platform | All | Severity | major | Priority | normal |
| Summary | Tweak STRICT-EQUAL? equivalences, add STRICT-EQUIV? function |
|---|---|
| Description |
Right now the equivalence functions in R3 follow a strict line of increasing equivalence, as documented here: http://www.rebol.net/wiki/Comparisons#EQUAL.3F However, making STRICT-EQUAL? a superset of EQUIV? has been causing some problems for a lot of programmers that do need what STRICT-EQUAL? adds (datatype, case, alias) but not what EQUIV? adds (binding, exact decimal). This could be solved by adding a new STRICT-EQUIV? function for STRICT-EQUAL?'s current behavior, and having STRICT-EQUAL? be a superset of EQUAL? instead. This would be the new hierarchy (more of a DAG now): - EQUAL?: Same as now. Ignores datatypes within certain type classes, bindings, case of strings and characters; considers word aliases to be equivalent (used for case insensitivity of words); uses approximate decimal comparison. - EQUIV?: Like EQUAL?, but pays attention to word bindings and uses more exact decimal comparison. - STRICT-EQUAL?: Like EQUAL?, but checks datatypes, and is case-sensitive with words, strings and characters. - STRICT-EQUIV?: Like STRICT-EQUAL?, but pays attention to word bindings and uses more exact decimal comparison. - SAME?: Identity, same as it is now. This behavior would extend to the corresponding NOT-* functions as well. We should also consider whether == should refer to STRICT-EQUAL? or STRICT-EQUIV?, as there is a slight difference between the decimal comparison used by EQUIV? and that used by SAME?. An alternative would be to come up with new operators for EQUIV? and STRICT-EQUIV?, but that has proved difficult so far. This proposal was suggested by Andreas in AltME. Related: #1133 |
| Example code |
| Assigned to | n/a | Fixed in | - | Last Update | 28-Feb-2014 23:54 |
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| Comments | |
|---|---|
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(0003044)
BrianH 20-Jan-2011 23:31 |
The main gotcha with this is that the exact decimal comparison performed by STRICT-EQUAL? now wouldn't have an operator, unless SAME? performs the same comparison. Ladislav, is there a difference between STRICT-EQUAL? and SAME? for decimals, and would this be a problem?
(Update) In AltME, Ladislav answered that for STRICT-EQUAL? -0.0 and +0.0 are considered equal, even with the more exact equivalence, while for SAME? they are considered different. If there are more differences he didn't mention them. |
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(0003054)
Carl 30-Jan-2011 20:26 |
Under consideration, if a satisfactory solution is agreed by Ladislav. |
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(0003058)
BrianH 30-Jan-2011 21:35 |
Alternate proposal for the operators: == keeps referring to STRICT-EQUAL? (by the definition in this ticket), === refers to STRICT-EQUIV? and !=== refers to STRICT-NOT-EQUIV?. This lets the majority of programmers continue to use the friendly approximate equivalence for ==, and makes the more exact equivalence available to the numerics people who understand the limits of IEEE754. |
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(0003077)
Ladislav 31-Jan-2011 12:11 |
I am afraid this means a lot of work, while the reasons to do it now are less convincing. Otherwise, I would not object against the proposed hierarchy, if that is what users request. |
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(0004279)
BrianH 28-Feb-2014 23:54 |
Note: "a lot of work" is not a blocker now if there's someone willing to do the work. Yay open source! And this is the exact kind of change that needs to go through before 3.0 - cleaning up basic semantics. |
| Date | User | Field | Action | Change |
|---|---|---|---|---|
| 28-Feb-2014 23:54 | BrianH | Comment : 0004279 | Added | - |
| 16-Feb-2013 03:09 | BrianH | Description | Modified | - |
| 31-Jan-2011 12:11 | Ladislav | Comment : 0003077 | Added | - |
| 30-Jan-2011 21:37 | BrianH | Comment : 0003044 | Modified | - |
| 30-Jan-2011 21:35 | BrianH | Comment : 0003058 | Added | - |
| 30-Jan-2011 20:26 | carl | Comment : 0003054 | Added | - |
| 30-Jan-2011 20:25 | carl | Status | Modified | submitted => waiting |
| 21-Jan-2011 00:50 | BrianH | Description | Modified | - |
| 21-Jan-2011 00:41 | BrianH | Description | Modified | - |
| 21-Jan-2011 00:33 | BrianH | Description | Modified | - |
| 21-Jan-2011 00:27 | BrianH | Description | Modified | - |
| 20-Jan-2011 23:35 | BrianH | Description | Modified | - |
| 20-Jan-2011 23:32 | BrianH | Description | Modified | - |
| 20-Jan-2011 23:31 | BrianH | Comment : 0003044 | Added | - |
| 20-Jan-2011 23:27 | BrianH | Severity | Modified | minor => major |
| 20-Jan-2011 23:27 | BrianH | Description | Modified | - |
| 20-Jan-2011 23:26 | BrianH | Ticket | Added | - |