Evaluating a local function within the global namespace

General Usage
1

Hi. I’ve written a tutoral program in which students submit an answer ans to an exercise using the format reply(ans). reply then passes ans deeper into a module within which ans is tested for correctness. The thing is, that ans might well contain variable names or functions that only exist in the Main namespace, and so I want - within my own module - to evaluate ans within the context Main. I tried something like this:

module Mod

export reply

iscorrect = (ans -> ans==myvar)

function reply( ans)
# Alternative 1:
iscorrect( Core.eval(Main,:ans))
# Alternative 2:
Core.eval(Main,:(iscorrect( ans)))
end

end # of Mod

using .Mod
myvar = 3
reply( 3)

I now have the two alternatives shown in the body of reply(): I can either evaluate :ans in Main or I can evaluate :(iscorrect(ans)) in Main. In the first case, iscorrect() doesn’t know about the existence of myvar, and in the second case, Main doesn’t know anything about the existence of iscorrect().

Clearly, in this example case, I could insert a Main evaluation of myvar within the mapping iscorrect; however in the tutorial program, iscorrect is just one of hundreds of correctness tests to be applied appropriately to different exercise replies.

Does anyone have any ideas how I could achieve this?
Thanks! :smile:

2

I’m a little confused by this example code. In this example ans is just a value—3 and myvar isn’t passed by the student at all so the checking code can’t know about it. How do you know that iscorrect is supposed to compare ans with myvar?

1 Like
3

An exercise requires from the student that she does certain things then reports back on the results. A typical exercise might be that the system asks her to create a vector myvect = collect(7:11) and reply with the value of the component myvect[3]. She enters reply(9), and the program checks whether this is indeed the third component of myvect.

I realise that this seems a little contrived in the context of my toy example, but in general, I want to be able to verify the correctness of arbitrary things she has tried out, and this involves evaluating expressions within her Main environment.

4

There is some reason to be so strict on how the things get done, instead of just making a test suit that tests if functions defined by the students always give the right answers given the correct inputs?

This is:

module Mod

export check_square

function check_square(f)
    for i in -10:10
        # Probably using @testset and @test from module `Test` is better
        @assert f(i) == i ^ 2 
    end

    ... # Other tests for each function.
end

end

using .Mod

f(x) = x^2

check_square(f)
5

Maybe you need to do more complicated things but for this example it doesn’t look like you need eval.

module Mod

export reply
iscorrect = (ans -> ans == Main.myvar)
reply(ans) = iscorrect(ans)

end # of Mod

using .Mod
myvar = 3
reply(3)
2 Likes
6

:smiley: Oh, how glad I am that this forum exists! Gunnar, you’ve saved my life! The students found the bug today and I need to fix it this evening. I would still like to hear if anyone has an answer to my original question, but in the meantime you’ve given me a fix that will get things moving in time for tomorrow. Thanks!