Part 27: Projects

Every other part of the course teaches one idea per lesson. This part does the opposite: each project is a complete small program that puts many ideas to work at once — a calculator that explains its errors, a word counter, a guessing game, a to-do list kept in a file, a command-line search tool. They are not meant to be read after Part 26. Each one is a checkpoint for an earlier part, and uses nothing the course has not taught by then, so you can stop after that part and build something real.

What you will learn

• How the single ideas of the lessons combine into a program with a design: small functions with one job each, data described by types, and Main reading like a summary.
• How to treat input as hostile: reading lines, parsing numbers, and telling the end of the input, a read error, a malformed number and an out-of-range one apart.
• How to model every way a program can fail as an error type, and when to stop, pass a failure on, or skip it and carry on.
• How to choose the right standard package for a job — collections, algorithms, time, randomness, entropy, files, JSON, regular expressions and the command line.
• How to run interactive programs and command-line tools, and which projects need a keyboard, a sound card or Windows.

Which part unlocks which project

The arrows point from the part you need to have finished to the projects you can build after it:

flowchart LR
    p3["Part 3<br/>Control flow"] --> thanks["Thanks"]
    p3 --> fizz["FizzBuzz"]
    p4["Part 4<br/>Functions"] --> temp["Temperature"]
    p5["Part 5<br/>Sequences"] --> prime["Prime"]
    p9["Part 9<br/>Errors"] --> calc["Calculator"]
    p16["Part 16<br/>Numbers"] --> circle["Circle"]
    p16 --> quad["Quadratic"]
    p17["Part 17<br/>Collections"] --> words["Word count"]
    p17 --> inv["Inventory"]
    p18["Part 18<br/>Algorithms"] --> stats["Statistics"]
    p20["Part 20<br/>Utilities"] --> guess["Guess"]
    p20 --> age["Age"]
    p20 --> pass["Password"]
    p20 --> launch["Launch"]
    p21["Part 21<br/>Data formats"] --> notes["Notes"]
    p24["Part 24<br/>Platform"] --> melody["Melody"]
    p26["Part 26<br/>Systems"] --> grep["Grep"]

Circle and Quadratic are really about Part 14: Text — reading and parsing a line — but they also borrow IsFinite and the Math package from Part 16, so they unlock there.

Lessons

Before you start

Pick the project for the part you have just finished, rather than reading this part in order. Each project page lists exactly which lessons it leans on, links them where they are used, and ends with exercises that extend the program — those are the real work.

Each project is a package in the Examples repository's Projects/ folder:

cd Examples/Projects/FizzBuzz
rux run

Most projects print the same output on every run. A few are different:

After this part

This is the end of the course. From here, the best next step is a program of your own — take the project closest to what you want to build and change it until it is yours. The Rux Reference has the full rules behind every lesson, the API reference covers the standard packages, and the cheat sheet keeps the syntax on one page. When you want to share what you made, Part 22: Packages shows how to turn it into a package others can depend on.