Examples

Browse every example in the repository, with its source code, command and recorded output where available.

The test corpus is the collection of programs used to check the compiler. On every commit, the tests build and run them in three configurations; examples that need an unavailable C library are skipped. Where a page shows recorded output below the command, the tests compare the program’s output with that text byte for byte.

Start with the first group, which introduces one idea at a time in reading order. These files are checked for compilation errors and formatting, but their output is not recorded or tested. The remaining groups make up the test corpus, with programs such as a JSON reader, a small language interpreter, a SQLite ledger and calculations using raylib.

Start here · Reading and processing text · Numbers and algorithms · Data structures · Files and the command line · C libraries · Threads · Games and simulations

• 68programs
• 120files
• 18,836lines

Start here

• 00-first

  8 lines

  A minimal program that prints a number, and the first one this compiler ran.

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• 01-points

  49 lines

  Define records, create values and call functions with method syntax.

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• 02-tokens

  53 lines

  Define a value with several possible forms and handle every case.

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• 03-fallible

  54 lines

  Return failures as values and handle them explicitly.

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• 04-loops

  72 lines

  Repeat work with two kinds of loop and mark each change to a value.

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• 05-mutation

  55 lines

  Change a copy without changing the original value.

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• 06-generics

  56 lines

  Write one function for several types and let the compiler infer the types at each call.

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• 07-strings

  66 lines

  Read text as bytes or as whole characters, depending on the task.

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• 08-ffi

  49 lines · uses C

  Use C libraries for features beyond the language basics.

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• 09-holes

  35 lines

  Mark unfinished code with ??? and see which type the compiler expects.

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• 10-maps

  63 lines

  Look up a map key and handle a missing entry explicitly.

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• 11-trees

  98 lines

  Build a tree whose nodes store their children as independent values.

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• 12-interpolation

  33 lines

  Put a value inside a string, and let the compiler say when it has no text.

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• 13-lease

  27 lines · uses C

  Hand a C library text it will keep, and say when you are done with it.

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Reading and processing text

• calculator

  901 lines · 5 modules

  A calculator that reads and evaluates arithmetic expressions with variables.

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• interpreter

  2,642 lines · 11 modules

  Read and run scripts written in a small language.

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• json

  674 lines · 3 modules

  Read a JSON document, describe its structure and print it in a consistent format.

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• markdown

  531 lines · 4 modules

  Convert Markdown to plain text, with the work split across modules.

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• csv

  193 lines

  Read a CSV table, including quoted fields, commas inside fields and doubled quotation marks.

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• ini

  247 lines

  Read a configuration file into sections and report invalid entries.

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• template

  235 lines

  Fill placeholders in a text template with values from a map.

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• rpn

  216 lines

  Evaluate reverse Polish expressions, where each operator follows its numbers.

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• assembler

  632 lines · 4 modules

  An assembler that translates instructions for a small simulated machine, then runs them.

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• roman

  168 lines

  Convert numbers to Roman numerals and back.

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• words

  161 lines

  Count how often each word appears in a passage.

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• wrap

  171 lines

  Wrap text to a chosen line width and test the boundary cases.

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Numbers and algorithms

• sieve

  185 lines

  Find prime numbers by crossing out multiples, then check the counts against published results.

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• nbody

  405 lines · uses C

  Simulate five bodies moving under gravity and check their energy against published results.

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• spectral

  267 lines · uses C

  Calculate the largest singular value of a matrix without storing the matrix.

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• fannkuch

  273 lines

  Try every ordering of seven numbered cards, flipping them until card 1 is on top.

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• binarytrees

  218 lines

  Build binary trees, visit their nodes and release the memory they use.

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• checksum

  738 lines · 4 modules

  Compute CRC-32 and Adler-32 checksums, and encode the same bytes as Base64.

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• diff

  254 lines

  Find changes between two versions by comparing what they have in common.

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• dates

  260 lines

  Count the days between two dates, including leap years.

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• floats

  192 lines

  Print and compare infinity and NaN, the special floating-point value meaning not a number.

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• widths

  185 lines

  Convert numbers between types and check what happens when they no longer fit.

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• palette

  179 lines

  Pack a colour into one integer, extract its parts and combine them again.

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Data structures

• query

  1,490 lines · 6 modules

  Create a table, save and read it back, then filter, join, sort and group its rows.

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• spreadsheet

  562 lines · 3 modules

  Read a spreadsheet file and evaluate its formulas.

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• tree

  192 lines · 2 modules

  Build an expression tree, then evaluate it, measure its depth and print it.

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• routes

  168 lines

  Find the shortest route between two stations.

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• deck

  187 lines

  Deal, cut, reverse and riffle a deck of values.

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• readings

  173 lines · 2 modules

  Summarise a week of sensor readings with map, filter, fold, find, any and all.

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• shapes

  181 lines · 6 modules

  Import the same module from files at different directory depths.

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Files and the command line

• todo

  334 lines · 2 modules

  Keep a to-do list in a file.

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• logs

  589 lines · 4 modules

  Turn a log file into a readable summary.

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• argv

  89 lines

  Two ways to read the arguments passed to a program.

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• tally

  224 lines · uses C

  Count lines, words and bytes received through standard input.

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• pipeline

  210 lines · 3 modules

  Read lines and produce a report using two modules with the same name.

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C libraries

• sqlite

  119 lines · uses C

  Open, query and close a SQLite database directly from Heroes.

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• ledger

  1,011 lines · 4 modules · uses C

  Keep a ledger in SQLite and check each total with a separate calculation.

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• curl

  99 lines · uses C

  Call libcurl from Heroes, including a function that accepts a variable number of arguments.

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• raylib

  145 lines · uses C

  Use raylib to calculate with colours, points and rectangles passed as C structs.

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• sdl

  65 lines · uses C

  Call SDL3 from Heroes and check which drawing drivers it provides.

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• ctime

  168 lines · uses C

  Read the parts of a calendar date from a C struct.

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Threads

• threads

  133 lines · threads

  Start threads and pass each one an integer to work with.

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• mandelbrot

  114 lines · threads

  Count the calculation steps needed for points in the Mandelbrot set, using several threads.

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• matmul

  113 lines · threads

  Multiply two matrices, assigning a band of rows to each thread.

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• dotproduct

  80 lines · threads

  Compute the dot product of two long vectors, using several threads.

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• montecarlo

  89 lines · threads

  Estimate pi by simulating dart throws, with a separate random seed for each thread.

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• nqueens

  101 lines · threads

  Count the ways to place eight queens on a chessboard so none can attack another.

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• collatz

  101 lines · threads

  Find the longest Collatz sequence below a chosen limit, using several threads.

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• firsthit

  101 lines · threads

  Search a long range with several threads to find the first position that meets a condition.

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• histogram

  100 lines · threads

  Count how often each digit appears, with one thread for each digit.

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• wordbands

  130 lines · threads

  Count words in text generated separately by each thread.

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Games and simulations

• adventure

  454 lines · 3 modules

  A text adventure that follows a script of player commands.

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• maze

  374 lines · 3 modules

  Find and draw the shortest path through a maze.

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• board

  295 lines

  A grid of cells that grow and die, with a scoreboard organised by two keys.

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Next: the language, one idea at a time, or the complete specification in one file to hand to a model. How to run an example.