Step 1: Create a trivial exercise

As a first simple step, let us create an exercise which requires no real effort from the student: any valid OCaml code will be a valid answer for this exercise.

Let us focus on test.ml:

open Test_lib
open Report

let () =
  set_result @@
  ast_sanity_check code_ast @@ fun () ->
    Message ([ Text "That was easy!" ], Success 1)

This code is executed to grade the student answer. It has access to all the toplevel definitions introduced by the student answer.

The interface for the module Test_lib can be found in test_lib.mli.

The interface for the module Report can be found in learnocaml_report.mli.

Test_lib.set_result waits for the final report. A value of type report can be built from the constructors defined in the module Report. Two functions are applied to get the final report: first, Test_lib.ast_sanity_check performs some basic verification on the OCaml source, typically that some forbidden modules are not used ; second, it calls the function starting from fun () -> ... to execute the user testing code.

The user testing code is responsible for three tasks: to test the student answer, to assign a grade to this answer, and to generate an informative report.

In that example, we do not test the user code: therefore only the typechecking and the sanity checks are performed. If these checks pass, then the report generates the message That was easy! and give 1 point to the student.

Do it yourself!

  1. Copy the files of this trivial exercise to your own exercises directory.
  2. Update index.json
  3. Build and run the new instance of your local learn-ocaml platform:
     learn-ocaml build; learn-ocaml serve

At this point, you should see the exercise in the instance opened on http://localhost:8080. Click on grade to get your point!