CodeRunner Documentation (V3.0.0)
8.2 Combinator-template grading
The ultimate in grading flexibility is achieved by use of the "Combinator template grading" option. In this mode the per-test template is not used. The combinator template is passed to the Twig template engine and the output program is executed in the usual way. Its output must now be a JSON-encoded object with two mandatory attributes: a fraction in the range 0 - 1, which specifies the fractional mark awarded to the question, and a feedbackhtml that fully defines the specific feedback to be presented to the student in place of the normal results table. It might still be a table, but any other HTML-supported output is possible such as paragraphs of text, canvases or SVG graphics. The result_columns field from the question editing form is ignored in this mode.
Combinator-template grading is intended for use where a result table is just not appropriate, e.g. if the question does not involve programming at all. As an extreme example, imagine a question that asks the student to submit an English essay on some topic and an AI grading program is used to mark and to generate a report on the quality of the essay for feedback to the student. [Would that such AI existed!]
The combinator-template grader has available to it the full list of all test cases and their attributes (testcode, stdin, expected, mark, display etc) for use in any way the question author sees fit. It is highly likely that many of them will be disregarded or alternatively have some meaning completely unlike their normal meaning in a programming environment. It is also possible that a question using a combinator template grader will not make use of test cases at all.