Functional Language Equivalents in Nushell

1st chunk of `book/nushell_map_functional.md`

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# Nu Map from Functional Languages

The idea behind this table is to help you understand how Nu builtins and plugins relate to functional languages. We've tried to produce a map of relevant Nu commands and what their equivalents are in other languages. Contributions are welcome.

Note: this table assumes Nu 0.43 or later.

| Nushell      | Clojure                      | Tablecloth (Ocaml / Elm)        | Haskell                  |
| ------------ | ---------------------------- | ------------------------------- | ------------------------ |
| append       | conj, into, concat           | append, (++), concat, concatMap | (++)                     |
| into binary  | Integer/toHexString          |                                 | showHex                  |
| count        | count                        | length, size                    | length, size             |
| date         | java.time.LocalDate/now      |                                 |                          |
| each         | map, mapv, iterate           | map, forEach                    | map, mapM                |
| exit         | System/exit                  |                                 |                          |
| first        | first                        | head                            | head                     |
| format       | format                       |                                 | Text.Printf.printf       |
| group-by     | group-by                     |                                 | group, groupBy           |
| help         | doc                          |                                 |                          |
| is-empty     | empty?                       | isEmpty                         |                          |
| last         | last, peek, take-last        | last                            | last                     |
| lines        |                              |                                 | lines, words, split-with |
| match        |                              | match (Ocaml), case (Elm)       | case                     |
| nth          | nth                          | Array.get                       | lookup                   |
| open         | with-open                    |                                 |                          |
| transpose    | (apply mapv vector matrix)   |                                 | transpose                |
| prepend      | cons                         | cons, ::                        | ::                       |

Title: Functional Language Equivalents in Nushell

Summary

This section provides a table mapping Nushell commands to their equivalent functions in functional languages like Clojure, Tablecloth (Ocaml/Elm), and Haskell. The table covers common commands for operations like appending, counting, iterating, grouping, and more, offering a reference for users familiar with functional programming concepts.