examples.md

Examples

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Annotated walkthroughs of fy programs, from simple to complex.

Factorial (examples/fact.fy)

Classic recursive factorial:

: fact
  dup 1 <=            ( is n <= 1? )
  [ drop 1 ]          ( base case: return 1 )
  [ dup 1- fact * ]   ( recursive: n * fact(n-1) )
  ifte
;

10 fact .              ( prints 3628800 )

Key concepts: word definition, recursion, ifte conditional.

Fibonacci (examples/fib.fy)

: fib
  dup 1 <=
  [ drop 1 ]
  [ dup 1- fib swap 2 - fib + ]
  ifte
;

10 fib .               ( prints 89 )

Naive doubly-recursive Fibonacci. Demonstrates that fy handles deep recursion through proper ARM64 call frames.

TAK Benchmark (examples/tak.fy)

The Takeuchi function — a classic benchmark for function call overhead:

: tak
  [ | x y z |
    y x >=
    [ z ]
    [
      x 1- y z tak
      y 1- z x tak
      z 1- x y tak
      tak
    ] ifte
  ] do
;

Demonstrates locals (| x y z |) for readable multi-argument words.

Loops (examples/loops.fy, examples/loop.fy)

Counted Loop with dotimes

5 [ "hello" s. .nl ] dotimes

Loop with repeat

5 [ dup . 1- dup ] repeat drop

Prints 5 4 3 2 1. The quote must leave a condition on TOS — repeat continues while it's non-zero.

Sierpinski Triangle (examples/sierp.fy)

Generates a PPM image of the Sierpinski triangle using bitwise AND:

: pixel
  & 0 = [ 0 0 0 ] [ 255 255 255 ] ifte
;

Each pixel's color is determined by x & y == 0. Demonstrates file I/O (spit), string building, and bitwise operations.

Functional Programming

Map, Reduce, Filter

( Square every element )
[1 2 3 4] [dup *] map          ( → [1 4 9 16] )

( Sum a list )
0 [1 2 3 4 5] [+] reduce       ( → 15 )

( Keep only values > 3 )
[1 2 3 4 5] [3 >] filter       ( → [4 5] )

( Side effects )
[1 2 3] \. each                 ( prints 1 2 3 )

Quote Manipulation

qnil                            ( empty quote [] )
42 qpush                        ( [42] )
99 qpush                        ( [42 99] )
qhead .                         ( prints 42 )

( Build a quote from words )
[] [\+ \- \*] \cat reduce       ( concatenate word-quotes )

FFI: libm Math Functions (examples/libm.fy)

:: _lib "/usr/lib/libm.dylib" dl-open ;

:: _sin  _lib "sin" dl-sym ;
:: _cos  _lib "cos" dl-sym ;
:: _pow  _lib "pow" dl-sym ;
:: _sqrt _lib "sqrt" dl-sym ;

: sin   _sin  bind: d:d ;
: cos   _cos  bind: d:d ;
: pow   _pow  bind: dd:d ;
: sqrt  _sqrt bind: d:d ;

3.14159 sin f.          ( ≈ 0.0 )
2.0 10.0 pow f.         ( 1024.0 )
144.0 sqrt f.           ( 12.0 )

Key pattern: :: evaluates dl-open/dl-sym once at compile time, then bind: generates inline calling code.

FFI: raylib Game Window (examples/raylib_hello.fy)

include "raylib.fy"

800 450 "Hello from fy!" InitWindow

[ WindowShouldClose not ] [
  BeginDrawing
    245 245 245 255 ClearBackground
    190 200 20 "fy says hello!" DrawText
  EndDrawing
] repeat

CloseWindow

A complete raylib window with a game loop. The raylib.fy file (auto-generated from raylib.ffi by gen-ffi) provides all the bindings.

FFI: Polyphonic Synthesizer (examples/raylib_synth_poly.fy)

A real-time polyphonic synthesizer using raylib audio:

struct: Voice
  f32 phase    f32 freq
  f32 attack   f32 decay
  f32 sustain  f32 release
  f32 env      i32 state
  i32 key      i32 active
;

Demonstrates:

• Struct definitions with field accessors
• Audio callbacks (callback: pi:v audio-fill)
• Thread-safe callbacks with private data stacks
• Real-time DSP with float math
• Complex control flow for ADSR envelopes

Modules: Import (examples/golden/import_basic.fy)

import "testlib"
5 testlib:double .      ( prints 10 )

Where testlib.fy defines:

: double  2 * ;

After import "testlib", all words gain a testlib: prefix.

Macros: Compile-Time Constants (examples/macro.fy)

: cfib  dup 1 <= [ drop 1 ] [ dup 1- cfib swap 2 - cfib + ] ifte ;

macro: const  peek-quote unpush do emit-lit ;

[10 cfib] const .       ( Fibonacci computed at compile time! )

The result (89) is baked into the binary — zero runtime cost.

macOS Liquid Glass (examples/glass.fy)

import "objc"

( ... create NSWindow, NSView, set up appearance ... )

Demonstrates calling Objective-C frameworks through objc_msgSend, selector registration, and class lookup — all via fy's FFI. See the objc.fy module for the ObjC bridge implementation.

Golden Tests

The examples/golden/ directory contains small focused tests for individual features. Each .fy file has a matching .expected file with the expected output. These serve as both tests and minimal examples:

Test	Feature
locals_basic	Local variable binding
locals_nested_shadow	Shadowing locals in nested quotes
ifte_basic_true/false	Basic conditional branching
ifte_do_question	do? conditional execution
quotes_do	Quote execution with do
map_basic	map over quotes
reduce_basic_sum	reduce for summation
ffi_strlen	FFI string length call
ffi_abs	FFI absolute value
float_basic	Float arithmetic
strings_basic	String operations
constant_basic	Compile-time constants
mutual_even_odd	Mutual recursion
recursion_sum	Basic recursion
import_basic	Module import
nested_loops	Nested dotimes