[Python][ArborGUI] Certain locset expressions generate errors

[brenthuisman]

Describe the bug

Not all locset expressions seem to be working. Take this Python script:

import arbor as arb

labels = arb.label_dict({'soma': '(tag 1)', 'axon': '(tag 2)',
                         'dend': '(tag 3)', 'apic': '(tag 4)',
                         'center': '(location 0 0.5)',
                         })

labels['reg1']= '(radius-lt (region "dend") 0.5)'
labels['reg2']= '(radius-lt (tag 3) 0.5)'
labels['reg3']= '(radius-gt (all) 0.5)'
labels['reg4']= '(branch 2)'
labels['reg5']= '(distal (all))'
labels['reg6']= '(radius_lt (all) 0.5)'

It terminates with the following:

Traceback (most recent call last):
  File "model.py", line 13, in <module>
    labels['reg6']= '(radius_lt (all) 0.5)'
RuntimeError: 
----- internal error -------------------------------------------
Error parsing the label: 'reg6' = '(radius_lt (all) 0.5)'

error in label description at 1:2: No matches for 'radius_lt' with 2 arguments: (region real)
  There are 0 potential candiates..

Please file a bug report with this full error message at:
    github.com/arbor-sim/arbor/issues
----------------------------------------------------------------

Possibly related: arbor-gui, trips over even more expressions.

• (radius-lt "dend" 0.5) produces:

[2020-11-12 13:17:23.984] [debug] called error  No matches for 'radius-lt' with 2 arguments: (unknown real)
  There are 1 potential candiates:
  Candidate 1  'radius-lt' with 2 arguments: (reg:region radius:real).!

• (radius-lt (tag 3) 0.5) produces:

[2020-11-12 13:14:31.491] [debug] called error Invalid locset description: '(radius-lt (tag 3) 0.5)' is neither a valid locset expression or locset label string!

• (branch 2) procudes:

[debug] called error Invalid locset description: '(branch 2)' is neither a valid locset expression or locset label string!

I've run the tests with the following addition:

    auto lt = reg::radius_lt(reg::tagged(3), 0.5);
    auto gt = reg::radius_gt(reg::tagged(3), 0.5);
    EXPECT_EQ(to_string(lt), "(radius-lt (tag 3) 0.5)");
    EXPECT_EQ(to_string(gt), "(radius-gt (tag 3) 0.5)");

which does not fail.

[bcumming]

Here are the docs for radius-lt:
https://arbor.readthedocs.io/en/latest/concepts/labels.html#label-radius-lt-reg-region-radius-real

The first error is because of a typo: radius_lt, not radius-lt.

The second error is because "dend" is not a valid region expression.

Try (radius-lt (region "dend") 0.5).

[bcumming]

error in label description at 1:2: No matches for 'radius_lt' with 2 arguments: (region real)
  There are 0 potential candiates..

This is saying that you called radius_lt with arguments of type region and real, and that there are zero versions of radius_lt (i.e. radius_lt is not a known region type).

No matches for 'radius-lt' with 2 arguments: (unknown real)
  There are 1 potential candiates:
  Candidate 1  'radius-lt' with 2 arguments: (reg:region radius:real).

Says that radius-lt is called with two arguments of type unknown and real, and there is one alternative that takes a region and a real. So you can infer that "dend" does not define a region.

[bcumming]

Finally, (branch 2) defines a region, not a locset. The error says '(branch 2)' is neither a valid locset expression or locset label string, which is correct.

[brenthuisman]

1. Good catch! That solves it.
2. I've tried (radius-lt (region "dend") 0.5) as well, it gives (in the gui):

[2020-11-12 16:31:14.365] [debug] called error Invalid locset description: '(radius-lt (region "dend") 0.5)' is neither a valid locset expression or locset label string!

The docs lead me to believe "a_valid_label" is a valid region, so if "dend" is defined, that should work, right? But, @thorstenhater mentioned he does not actually set up a label_dict, so that must the cause.
3. I see now that this was actually thought through :) Regions and (sets of) locations are different categories!

[bcumming]

Indeed.
Text labels can be given to regions and locsets, and our little DSL requires that everything is typed, where the possible types are:

region, locset, string, real, int

[brenthuisman]

The docs state that "soma" is a shortcut for the region "soma". What does shortcut mean then? Apparently it does not evaluate to a region.

[thorstenhater]

This works even w/o a label_dict
(radius-lt (region "rad") 0.5)

[brenthuisman]

Not in the GUI however. I'm trying to write a correct test in the C++ tests (#1230) but there I run into another issue.

[thorstenhater]

For reference: The issue in the GUI was unrelated, putting a region expression into a locset control and vice versa will return errors since the expressions are coerced to the respective type.