Completing Undefined

So far, all we have done is added a Mathics3 Builtin class for Undefined and filled out the docstring to describe it and give some examples. We haven’t filled out any implementation.

Some of the remaining things have already been filled out, but some haven’t. Here all we need to do is set some class variables:

class Undefined(Builtin):
    Undefined symbol/value (<url>:WMA:</url>)
    ... Same as before

attributes = A_PROTECTED
summary_text = "undefined value"

The attributes class variable sets the kind of properties or “Attributes” that this Mathics3 Symbol has. See Attributes for more information about what an attribute is and what values it might have. Here, A_PROTECTED is a mask value that indicates that the Symbol Undefined starts off not being able to be reassigned to. There is an Unprotect function that can change this though.

It so happens that all Built-in symbols are functions start out this way, so setting this class variable is not needed. However I like to be explicit. See Adding Builtin Function KroneckerProduct for an example we need to set attributes other than “protected”.

Assigning to summary_text does two things:

  • It adds this text in Mathics3 Django in the list of functions in the section it appears

  • It supplies text in the command-line for ? or Information where Longform option is set to False.

To make sure we have summary_text assigned a value, there is a unit test that checks this.

Now let us look at this in the Django front end. As noted above, the section head “Mathematical Constants”. Here is a screenshot for that section:

summary list for Mathematical Constants

I searched on the prefix “Mathematical Con” which is the leading prefix that makes “Mathematical Constants” unique.

To see the effect of summary_text in the CLI, we will use the stripped down mathics program that comes with mathics-core:

$ mathics

Mathics3 5.0.3dev0
on CPython 3.8.12 (heads/v2.3.4.1_release:4a6b4d3504, Jun  3 2022, 15:46:12)

In[1]:= ?Undefined
undefined value
Out[1]= Null

The completed class definition for Undefined can be found on github.