Turn exercise 003 into practice

[cuihtlauac]

Extract the OCaml code from the markdown file corresponding to this exercise. The file is: data/exercise/003_NAME.md (where 003 is the number from the title of this issue and NAME is the rest of the file name, for instance data/exercise/001_tail.md is the file which corresponds to exercise 001). Use the code in this file to create a folder practice/003 (using this same number).

Populate the 003 folder with (almost) the same files as in folders practice/001 and practice/002 (they are examples).

Three files are different in each folder:

1. practice/003/ex.ml: it contains the function's signature, which needs to be implemented by the learner;
2. practice/003/work/impl.ml: it includes the template meant to be filed by the learner;
3. practice/003/answer/impl.ml: consists of the solution from the original markdown file.

The examples included in the original markdown file must be turned into test cases in the practice/003/ex.ml file.

Folder structure to create:

practice/003/
├── answer
│   ├── impl.ml
│   └── test
│       ├── dune
│       └── run.ml
├── dune
├── dune-project
├── ex.ml
└── work
    ├── impl.ml
    └── test
        ├── dune
        └── run.ml

[MissJae]

Hello, I'm Jennifer an Outreachy applicant. Can I do this?

[cuihtlauac]

Hello, I'm Jennifer an Outreachy applicant. Can I do this?

Sure, it's meant for that :-)