Exercise checking should include an argument indicating which type of check is being perfomed

[gadenbuie]

If we add a type stage argument to the function signature of the exercise checker, learnr can communicate which checking step is being performed.

Practically speaking this would allow gradethis to relax the "always return a grade" constraint for code checking, which would allow grading to do a first-pass code check before full evaluation.

The impact would be small for exercise checking functions that include .... Alternatively, the checking step can be inferred from the values of particular arguments as described in Exercises - Custom Checking, but it'd be cleaner to simply tell the checker what step is being performed.

cc @schloerke

[schloerke]

it'd be cleaner to simply tell the checker what step is being performed.

Agreed!