Coding for beginners: a robot and blocks

How the result is calculated

1. A program is made of blocks. Each block matches one or more lines of Python generated beside it, so while the program runs, the block and its line light up together.
2. The robot lives on a grid of at most 8 × 8 squares. A square is free, a wall, a coin or the goal with a flag; the edge of the grid is a wall. The robot stands on one square and faces one of four directions.
3. When you press Run, the whole run is worked out in advance and then played back. Every command carried out is a step, and so is every condition checked (“Is the path ahead clear? Yes”). The same program on the same map always runs the same way.
4. A level is solved when the program finishes without an error, the robot ends on the goal (if the map has one) and no coin is left. Some levels have two or three maps and the program must pass them all: the map on screen runs visibly, the others are checked quietly, and if one of them fails, the game switches to it and shows why.
5. A run stops with an error at the block that caused it: the robot would hit a wall, it would pick up a coin where there is none, or the program is empty. After 1,000 steps a run stops as an endless loop, and a function that calls itself more than 50 levels deep stops as endless calling.
6. Some levels allow only a limited number of blocks. Every block counts, including the blocks inside loops, conditions and functions; a block that holds other blocks counts once.
7. The program you are working on in each level and the list of solved levels are stored only in your browser’s storage.

Assumptions and limits

• The robot knows only 4 commands (move forward, turn left, turn right, pick up a coin) and 5 conditions (path clear ahead, on the left and on the right, standing on a coin, at the goal), each of them also negated.
• There are no variables, no arithmetic with numbers and no functions of your own with parameters. The level sets up each function (its name and purpose); you build only what it does.
• The Python is read-only: it shows what the program looks like as text, but you can’t type it yet. Commands such as move() or path_ahead() are functions of this game, not part of Python, so the code on its own won’t run outside the game.
• The names in Python are in English (move, turn_left, pick_coin…), as in real programs; the blocks are in the language of the page.
• The robot does exactly what the program says; it doesn’t guess or fix anything. That is not a shortcoming: it is the main thing to learn here.

We designed the maps and levels ourselves as exercises; they are not data. The idea of a robot led through a grid by a program comes from Karel the Robot, which Richard E. Pattis described in 1981 as a first lesson in programming.

Data sources and the period they hold for

Every number a calculator starts with or computes from comes from one of the sources below. Series names are given as the publisher names them. Each row shows the period the data refer to and, where we record it, the day we downloaded them. Official data can be months old when they are published, so check the current figure before you decide.

Official

Published by a central bank, a statistical office, the European Union or another public body.

Research or industry data

A dataset of a university, an index provider, an industry association or a data vendor.

Reported

A figure of an official body that we know only from the press and did not check in the primary source. Treat it as approximate.

Example

A round number of ours, not a statistic. Replace it with your own.