Better exercises for lambda and stl

[HereThereBeDragons]

After having a longer discussion yesterday with bernhard, i got the following idea how the difficulty of understanding lambdas and stl could be eased.

I would suggest the following exercises (in order of execution):

1. lambda simple: exercise to write simple lambda function, maybe even start with rewritting an existing function by a lambda - no usage of stl
2. lambda and stl - simple: rewrite an (existing & fully functioning) program that uses stl with function object to replace these function objects with lambdas
3. lambda and stl - advanced: have an unfinished program where stl functions and their respective lambdas must be added. could be that in the readme there is a list of possible stl functions to decide from

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[bernhardmgruber]

Thx @HereThereBeDragons for sketching that outline! I indeed think that the stl exercise mixes a lot of things at the moment and that we could improve it.

Historically, we had separate exercises for the STL and for lambdas. However: in the opposite order. We first introduced the STL using function objects, and then we had an exercise to convert a program using STL with function objects into a program using STL and lambdas. I campaigned for merging the two because I don't want students to practice writing function objects. Lambdas are just superior in most situations. That explains the status quo.

I especially like your suggestion 1. of having a dedicated exercise on lambda functions without any STL. I would then still combine 2. and 3., because the starting point for the current stl exercise already gives you all the names of the STL functions you should use. I think we may even had your suggestion 2. at some point, but it took too long for the students to figure out how to refactor a non-STL program into an STL one. Which is why we provide the combined approach.

[HereThereBeDragons]

I personally would keep 2. and 3. separate and have 3. as bonus exercise for the essential course and as a quick refresher exercise for the advanced course.

Also I personally would vary a bit that you use more than just 2 STL functions

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