Handle RuleDelayed in Map over Association expressions by mmatera · Pull Request #1694 · Mathics3/mathics-core

mmatera · 2026-02-12T11:57:29Z

One slight change over #1692. Also, I add a comment about differences with WMA output in the case that the Association expression does not have the form Association[__(Rule|RuleDelayed)].

rocky · 2026-02-12T12:03:15Z

LGTM. Thanks for the generalization and clarification.

Li-Xiang-Ideal · 2026-02-12T12:13:35Z

btw now MapAt maps on values for Association[__Rule] only:

mathics-core/mathics/eval/functional/apply_fns_to_lists.py

Lines 41 to 46 in a60d4f7

    
           if hasattr(replace_element, "head") and replace_element.head is SymbolRule: 
        
               new_elements[j] = Expression( 
        
                   SymbolRule, 
        
                   replace_element.elements[0], 
        
                   Expression(f, replace_element.elements[1]), 
        
               )

rocky · 2026-02-12T13:22:48Z

mathics/builtin/functional/apply_fns_to_lists.py

            #

-            if is_association and level.has_form(("Rule", "RuleDeyaled"), 2):
+            if is_association and level.has_form(("Rule", "RuleDelayed"), 2):


This mistake wasn't caught in the existing tests. So, probably a test needs to be added here for the new features added.

The question is, what should we test? For the full behavior, I have in mind a bunch of tests, that in the current implementation would not pass. The example in the comment is one of them.
To match with the WMA behavior, this method should be rewritten, and probably it would be also be interesting to define a specific class (like ListExpression) to store valid Association expressions. None of this would be too complicated, but right now I do not have the time to handle it.
What I could do is to list the tests here, or just add the tests to a pytest module, and mark them as xfail.

The question is, what should we test?

So you are saying that nothing in this PR right now benefits a user? There is promise, though, that one day it will?

For the full behavior, I have in mind a bunch of tests, that in the current implementation would not pass. The example in the comment is one of them. To match with the WMA behavior, this method should be rewritten, and probably it would be also be interesting to define a specific class (like ListExpression) to store valid Association expressions. None of this would be too complicated, but right now I do not have the time to handle it. What I could do is to list the tests here, or just add the tests to a pytest module, and mark them as xfail.

Yes, it is better to add xfail or commented-out tests now while the issue is fresh in your mind rather than do it later. Thanks.

The question is, what should we test?

So you are saying that nothing in this PR right now benefits a user? There is promise, though, that one day it will?

For the full behavior, I have in mind a bunch of tests, that in the current implementation would not pass. The example in the comment is one of them. To match with the WMA behavior, this method should be rewritten, and probably it would be also be interesting to define a specific class (like ListExpression) to store valid Association expressions. None of this would be too complicated, but right now I do not have the time to handle it. What I could do is to list the tests here, or just add the tests to a pytest module, and mark them as xfail.

Yes, it is better to add xfail or commented-out tests now while the issue is fresh in your mind rather than do it later. Thanks.

This PR improves handling of some typical cases, but to cover the most general situation, we need to reimplement this.

For the full behavior, I have in mind a bunch of tests, that in the current implementation would not pass. The example in the comment is one of them. To match with the WMA behavior, this method should be rewritten, and probably it would be also be interesting to define a specific class (like ListExpression) to store valid Association expressions. None of this would be too complicated, but right now I do not have the time to handle it. What I could do is to list the tests here, or just add the tests to a pytest module, and mark them as xfail.

Yes, it is better to add xfail or commented-out tests now while the issue is fresh in your mind rather than do it later. Thanks.

This PR improves handling of some typical cases, but to cover the most general situation, we need to reimplement this.

It occurs to me that it might be good to open an issue with this information, so we don't forget after this PR is merged. Thanks.

I just opened a related issue #1696, with the basic content of this discussion.

rocky · 2026-02-12T16:27:17Z

test/builtin/list/test_association.py

+            "Map[F, Association[a->1, b:>Association[p->3,q->4]], {0}]",
+            None,
+            "F[Association[a->1, b:>Association[p->3, q->4]]]",
+            "Special behavior happends at the first level.",


happends -> occurs

rocky · 2026-02-12T16:27:47Z

test/builtin/list/test_association.py

+            "Map[F, Association[a->1, b:>Association[p->3,q->4]], {1}]",
+            None,
+            "Association[a->F[1], b:>F[Association[p->3, q->4]]]",
+            "Special behavior happends at the first level.",


happends -> occurs

rocky · 2026-02-12T16:28:05Z

test/builtin/list/test_association.py

+            "Map[F, Association[a->1, b:>Q[p->3, q->4]], {2}]",
+            None,
+            "Association[a->1, b:>Q[F[p->3],F[q->4]]]",
+            "Special behavior happends at the first level.",


happends -> occurs

mmatera · 2026-02-12T22:13:41Z

btw now MapAt maps on values for Association[__Rule] only:

mathics-core/mathics/eval/functional/apply_fns_to_lists.py

Lines 41 to 46 in a60d4f7

if hasattr(replace_element, "head") and replace_element.head is SymbolRule:

new_elements[j] = Expression(

SymbolRule,

replace_element.elements[0],

Expression(f, replace_element.elements[1]),

)

thanks for the observation!

rocky · 2026-02-16T17:13:38Z

Let's merge. If there are other changes that can be done in another PR.

handle RuleDelayed in Map over Association expressions. Adding a comment

c489245

rocky reviewed Feb 12, 2026

View reviewed changes

mmatera added 2 commits February 12, 2026 12:43

fix typo. Add tests

6c07659

merge

0741f67

mmatera force-pushed the more_on_fix_map branch from 77c564d to 0741f67 Compare February 12, 2026 15:45

rocky reviewed Feb 12, 2026

View reviewed changes

fix typos

0d3b996

mmatera mentioned this pull request Feb 13, 2026

Improve implementation of Association and associated functions #1696

Open

Merge branch 'master' into more_on_fix_map

fecadef

rocky merged commit 4ec3e0b into master Feb 16, 2026
21 checks passed

rocky deleted the more_on_fix_map branch February 16, 2026 17:13

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Li-Xiang-Ideal commented Feb 12, 2026

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mmatera commented Feb 12, 2026

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rocky commented Feb 16, 2026

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rocky Feb 12, 2026 •

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