Missing run-time check for correct number of arguments for display() and error()

[btzy]

The following call should be an error according to the spec, but is currently not an error:

display(1,"T",3);

(Note that display() is caught.)

It is a problem (and perhaps confusing for students) because:

• It does not follow the spec
• Source-defined functions and other stdlib functions are checked as per #346, so not checking display() and error() is even more surprising

[dtlay]

could you help to review pr #732? it would be easy to do a length check of the arguments with the newer implementation. thanks!

[martin-henz]

Yes, error() and display() give runtime error, but passing more than two arguments leads to silently ignoring the extra arguments. Should be an easy fix.

[RichDom2185]

Perhaps beyond just a runtime check, we also want to support type-checking for typed variants (see #1398).