Learn Io - 10 Code Examples & CST Typing Practice Test

Io is a small, prototype-based, object-oriented programming language designed for simplicity, concurrency, and rapid development of distributed applications. It emphasizes minimal syntax, message-passing, and highly dynamic objects.

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Io Counter and Theme Toggle Io Fibonacci Sequence Io Factorial Calculator Io Prime Checker Io Sum of List Io Reverse String Io Multiplication Table Io Celsius to Fahrenheit Io Simple Alarm Simulation Io Random Walk Simulation

Learn IO with Real Code Examples

Updated Nov 20, 2025

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Code Sample Descriptions

Io Counter and Theme Toggle

count := 0
isDark := false

updateUI := method(
    write("Counter: " .. count .. "\n")
    write("Theme: " .. (if(isDark, "Dark", "Light")) .. "\n")
)

increment := method(
    count = count + 1
    updateUI()
)

decrement := method(
    count = count - 1
    updateUI()
)

reset := method(
    count = 0
    updateUI()
)

toggleTheme := method(
    isDark = !isDark
    updateUI()
)

# Simulate actions
updateUI()
increment()
increment()
toggleTheme()
decrement()
reset()

Demonstrates a simple counter with theme toggling using Io objects and message passing.

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Io Fibonacci Sequence

a := 0
b := 1
write(a .. "\n")
write(b .. "\n")
for(i, 1, 8, do(
    c := a + b
    write(c .. "\n")
    a := b
    b := c
))

Generates the first 10 Fibonacci numbers.

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Io Factorial Calculator

fact := method(n, if(n <= 0, 1, n * fact(n-1)))
write(fact(5) .. "\n")

Calculates factorial of a number recursively.

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Io Prime Checker

isPrime := method(n, do(
    if(n <= 1, return(false))
    for(i, 2, n-1, if(n % i == 0, return(false)))
    return(true)
))
write(if(isPrime(13), "Prime\n", "Not Prime\n"))

Checks if a number is prime.

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Io Sum of List

lst := list(1,2,3,4,5)
sum := 0
foreach(x, lst, sum = sum + x)
write(sum .. "\n")

Calculates sum of a list of numbers.

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Io Reverse String

s := "HELLO"
r := s reverse
write(r .. "\n")

Reverses a string.

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Io Multiplication Table

n := 5
for(i, 1, 10, write(n .. " x " .. i .. " = " .. (n*i) .. "\n"))

Prints multiplication table of a number.

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Io Celsius to Fahrenheit

c := 25
f := (c * 9 / 5) + 32
write(f .. "\n")

Converts Celsius to Fahrenheit.

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Io Simple Alarm Simulation

temp := 80
thresh := 75
write(if(temp > thresh, "Alarm: Temperature Too High!", "Temperature Normal") .. "\n")

Simulates an alarm if a threshold is exceeded.

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Io Random Walk Simulation

steps := 10
pos := 0
for(i,1,steps, do(
    if(rand() < 0.5, pos = pos + 1, pos = pos - 1)
    write(pos .. "\n")
))

Simulates a 1D random walk.

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Frequently Asked Questions about Io

What is Io?

What are the primary use cases for Io?

Scripting and automation. Embedded system programming. Prototyping distributed applications. Rapid development of domain-specific languages. Concurrent and asynchronous programming

What are the strengths of Io?

Extremely lightweight and portable. Highly dynamic and flexible. Excellent for prototyping and experimentation. Concurrency support via coroutines. Easy to embed in other applications

What are the limitations of Io?

Small community and ecosystem. Limited libraries compared to mainstream languages. Not commonly used in enterprise production systems. Performance may lag for heavy computation. Steep learning curve for developers unfamiliar with prototype-based design

How can I practice Io typing speed?

CodeSpeedTest offers 10+ real Io code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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Code Sample Descriptions

Io Counter and Theme Toggle

count := 0
isDark := false

updateUI := method(
    write("Counter: " .. count .. "\n")
    write("Theme: " .. (if(isDark, "Dark", "Light")) .. "\n")
)

increment := method(
    count = count + 1
    updateUI()
)

decrement := method(
    count = count - 1
    updateUI()
)

reset := method(
    count = 0
    updateUI()
)

toggleTheme := method(
    isDark = !isDark
    updateUI()
)

# Simulate actions
updateUI()
increment()
increment()
toggleTheme()
decrement()
reset()

Demonstrates a simple counter with theme toggling using Io objects and message passing.

Let’s Try →

Io Fibonacci Sequence

a := 0
b := 1
write(a .. "\n")
write(b .. "\n")
for(i, 1, 8, do(
    c := a + b
    write(c .. "\n")
    a := b
    b := c
))

Generates the first 10 Fibonacci numbers.

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Io Factorial Calculator

fact := method(n, if(n <= 0, 1, n * fact(n-1)))
write(fact(5) .. "\n")

Calculates factorial of a number recursively.

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Io Prime Checker

isPrime := method(n, do(
    if(n <= 1, return(false))
    for(i, 2, n-1, if(n % i == 0, return(false)))
    return(true)
))
write(if(isPrime(13), "Prime\n", "Not Prime\n"))

Checks if a number is prime.

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Io Sum of List

lst := list(1,2,3,4,5)
sum := 0
foreach(x, lst, sum = sum + x)
write(sum .. "\n")

Calculates sum of a list of numbers.

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Io Reverse String

s := "HELLO"
r := s reverse
write(r .. "\n")

Reverses a string.

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Io Multiplication Table

n := 5
for(i, 1, 10, write(n .. " x " .. i .. " = " .. (n*i) .. "\n"))

Prints multiplication table of a number.

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Io Celsius to Fahrenheit

c := 25
f := (c * 9 / 5) + 32
write(f .. "\n")

Converts Celsius to Fahrenheit.

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Io Simple Alarm Simulation

temp := 80
thresh := 75
write(if(temp > thresh, "Alarm: Temperature Too High!", "Temperature Normal") .. "\n")

Simulates an alarm if a threshold is exceeded.

Let’s Try →

Io Random Walk Simulation

steps := 10
pos := 0
for(i,1,steps, do(
    if(rand() < 0.5, pos = pos + 1, pos = pos - 1)
    write(pos .. "\n")
))

Simulates a 1D random walk.

Let’s Try →

Frequently Asked Questions about Io

What is Io?

What are the primary use cases for Io?

Scripting and automation. Embedded system programming. Prototyping distributed applications. Rapid development of domain-specific languages. Concurrent and asynchronous programming

What are the strengths of Io?

Extremely lightweight and portable. Highly dynamic and flexible. Excellent for prototyping and experimentation. Concurrency support via coroutines. Easy to embed in other applications

What are the limitations of Io?

How can I practice Io typing speed?

CodeSpeedTest offers 10+ real Io code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.