Rewriting standard list functions (map, fold, sum, etc.) is a good entry-level exercise. A λ-calculus interpreter can be used as an intermediate level exercise

Rewriting standard list functions (map, fold, sum, etc.) is a good entry-level exercise. A λ-calculus interpreter can be used as an intermediate level exercise. It is in particularly valuable in the context of solidifying one's understanding of functional programming. You can also use "standard" textbooks, such as the SICP [0], and perform the exercises using the language of your choice, instead of Scheme/LISP. [0]: https://mitp-content-server.mit.edu/books/content/sectbyfn/books_pres_0/6515/sicp.zip/full-text/book/book-Z-H-4.html#%_toc_start https://mitp-content-server.mit.edu/books/content/sectbyfn/b...