Learn APL with Real Code Examples

Updated Nov 20, 2025

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Code Sample Descriptions

APL Counter and Theme Toggle

count ← 0
isDark ← 0

updateUI ← {
    'Counter: ',⍕count
    'Theme: ',(('Light','Dark')[isDark+1])
}

increment ← {
    count ← count + 1
    updateUI ⍬
}

decrement ← {
    count ← count - 1
    updateUI ⍬
}

reset ← {
    count ← 0
    updateUI ⍬
}

toggleTheme ← {
    isDark ← 1 - isDark
    updateUI ⍬
}

⎕ ← 'Simulate actions'
updateUI ⍬
increment ⍬
increment ⍬
toggleTheme ⍬
decrement ⍬
reset ⍬

Demonstrates a simple counter with theme toggling using APL variables and array-oriented expressions.

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APL Fibonacci Sequence

fib ← 0 1
10 {fib ← fib , +/¯2↑fib} ⍬
fib

Generates first 10 Fibonacci numbers using APL array operations.

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APL Factorial Calculator

n ← 5
×/⍳n

Calculates factorial of a number using APL product of integers.

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APL Prime Checker

n ← 13
(2≤⍳n-1) / n|⍳n-1 ⍝ returns 0 for prime

Checks if a number is prime using modulo and all.

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APL Sum of Array

+/ 1 2 3 4 5

Calculates the sum of an array.

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APL Reverse String

⍞ ← 'HELLO'⌽'HELLO'

Reverses a string.

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APL Multiplication Table

n ← 5
n x ⍳10

Generates multiplication table for a number.

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APL Celsius to Fahrenheit

c ← 25
f ← c x 9 ÷ 5 + 32

Converts Celsius to Fahrenheit.

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APL Simple Alarm Simulation

temp ← 80
thresh ← 75
(temp>thresh)/'Alarm: Temp Too High!'

Simulates an alarm if threshold exceeded.

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APL Random Walk Simulation

steps ← 10
pos ← 0
{pos ← pos + 2x?2-1}⍣steps ⍬

Simulates a 1D random walk using APL random numbers.

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Code Sample Descriptions

APL Counter and Theme Toggle

count ← 0
isDark ← 0

updateUI ← {
    'Counter: ',⍕count
    'Theme: ',(('Light','Dark')[isDark+1])
}

increment ← {
    count ← count + 1
    updateUI ⍬
}

decrement ← {
    count ← count - 1
    updateUI ⍬
}

reset ← {
    count ← 0
    updateUI ⍬
}

toggleTheme ← {
    isDark ← 1 - isDark
    updateUI ⍬
}

⎕ ← 'Simulate actions'
updateUI ⍬
increment ⍬
increment ⍬
toggleTheme ⍬
decrement ⍬
reset ⍬

Demonstrates a simple counter with theme toggling using APL variables and array-oriented expressions.

Let’s Try →

APL Fibonacci Sequence

fib ← 0 1
10 {fib ← fib , +/¯2↑fib} ⍬
fib

Generates first 10 Fibonacci numbers using APL array operations.

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APL Factorial Calculator

n ← 5
×/⍳n

Calculates factorial of a number using APL product of integers.

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APL Prime Checker

n ← 13
(2≤⍳n-1) / n|⍳n-1 ⍝ returns 0 for prime

Checks if a number is prime using modulo and all.

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APL Sum of Array

+/ 1 2 3 4 5

Calculates the sum of an array.

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APL Reverse String

⍞ ← 'HELLO'⌽'HELLO'

Reverses a string.

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APL Multiplication Table

n ← 5
n x ⍳10

Generates multiplication table for a number.

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APL Celsius to Fahrenheit

c ← 25
f ← c x 9 ÷ 5 + 32

Converts Celsius to Fahrenheit.

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APL Simple Alarm Simulation

temp ← 80
thresh ← 75
(temp>thresh)/'Alarm: Temp Too High!'

Simulates an alarm if threshold exceeded.

Let’s Try →

APL Random Walk Simulation

steps ← 10
pos ← 0
{pos ← pos + 2x?2-1}⍣steps ⍬

Simulates a 1D random walk using APL random numbers.

Let’s Try →