Learn Rebol - 10 Code Examples & CST Typing Practice Test

REBOL (Relative Expression-Based Object Language) is a lightweight, cross-platform programming language designed for network communications, data exchange, and scripting. It emphasizes simplicity, human-readable syntax, and rapid development of distributed applications.

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

Learn REBOL with Real Code Examples

Updated Nov 20, 2025

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Code Sample Descriptions

Rebol Counter and Theme Toggle

count: 0
isDark: false

updateUI: func [] [
    print join "Counter: " count
    print join "Theme: " (either isDark ["Dark"] ["Light"])
]

increment: func [] [
    count: count + 1
    updateUI
]

decrement: func [] [
    count: count - 1
    updateUI
]

reset: func [] [
    count: 0
    updateUI
]

toggleTheme: func [] [
    isDark: not isDark
    updateUI
]

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

Demonstrates a simple counter with theme toggling using Rebol variables and functions.

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Rebol Fibonacci Sequence

a: 0
b: 1
print a
print b
foreach i 1 2 3 4 5 6 7 8 [
    c: a + b
    print c
    a: b
    b: c
]

Generates first 10 Fibonacci numbers.

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Rebol Factorial Calculator

fact: func [n][
    either n = 0 [1] [n * fact n - 1]
]
print fact 5

Calculates factorial of a number.

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Rebol Prime Checker

is-prime?: func [n][
    if n < 2 [return false]
    foreach i 2 to n - 1 [
        if n // i = 0 [return false]
    ]
    true
]
print either is-prime? 13 ["Prime"] ["Not Prime"]

Checks if a number is prime.

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Rebol Sum of Block

lst: [1 2 3 4 5]
sum: 0
foreach n lst [sum: sum + n]
print sum

Calculates the sum of a block of numbers.

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Rebol Reverse String

s: "HELLO"
r: reverse s
print r

Reverses a string.

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Rebol Multiplication Table

n: 5
foreach i 1 2 3 4 5 6 7 8 9 10 [
    print rejoin [n " x " i " = " n * i]
]

Prints multiplication table of a number.

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Rebol Celsius to Fahrenheit

c: 25
f: (c * 9 / 5) + 32
print f

Converts Celsius to Fahrenheit.

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Rebol Simple Alarm Simulation

temp: 80
thresh: 75
print either temp > thresh ["Alarm: Temperature Too High!"] ["Temperature Normal"]

Simulates an alarm when temperature exceeds a threshold.

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Rebol Random Walk Simulation

steps: 10
pos: 0
foreach i 1 2 3 4 5 6 7 8 9 10 [
    if random 1 < 0.5 [pos: pos + 1] [pos: pos - 1]
    print pos
]

Simulates a 1D random walk.

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Frequently Asked Questions about Rebol

What is Rebol?

What are the primary use cases for Rebol?

Network protocols and communication. Scripting and automation. Rapid prototyping of applications. Data exchange with custom dialects. Embedded or lightweight distributed applications

What are the strengths of Rebol?

Extremely lightweight and portable. Rapid development with concise syntax. Excellent for networked or distributed applications. Powerful for creating domain-specific languages. Runs on many platforms including embedded systems

What are the limitations of Rebol?

Small user community compared to mainstream languages. Limited libraries and third-party ecosystem. Not widely adopted in enterprise production systems. Performance not optimized for compute-intensive tasks. Steep learning curve for complex dialects

How can I practice Rebol typing speed?

CodeSpeedTest offers 10+ real Rebol 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

Rebol Counter and Theme Toggle

count: 0
isDark: false

updateUI: func [] [
    print join "Counter: " count
    print join "Theme: " (either isDark ["Dark"] ["Light"])
]

increment: func [] [
    count: count + 1
    updateUI
]

decrement: func [] [
    count: count - 1
    updateUI
]

reset: func [] [
    count: 0
    updateUI
]

toggleTheme: func [] [
    isDark: not isDark
    updateUI
]

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

Demonstrates a simple counter with theme toggling using Rebol variables and functions.

Let’s Try →

Rebol Fibonacci Sequence

a: 0
b: 1
print a
print b
foreach i 1 2 3 4 5 6 7 8 [
    c: a + b
    print c
    a: b
    b: c
]

Generates first 10 Fibonacci numbers.

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Rebol Factorial Calculator

fact: func [n][
    either n = 0 [1] [n * fact n - 1]
]
print fact 5

Calculates factorial of a number.

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Rebol Prime Checker

is-prime?: func [n][
    if n < 2 [return false]
    foreach i 2 to n - 1 [
        if n // i = 0 [return false]
    ]
    true
]
print either is-prime? 13 ["Prime"] ["Not Prime"]

Checks if a number is prime.

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Rebol Sum of Block

lst: [1 2 3 4 5]
sum: 0
foreach n lst [sum: sum + n]
print sum

Calculates the sum of a block of numbers.

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Rebol Reverse String

s: "HELLO"
r: reverse s
print r

Reverses a string.

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Rebol Multiplication Table

n: 5
foreach i 1 2 3 4 5 6 7 8 9 10 [
    print rejoin [n " x " i " = " n * i]
]

Prints multiplication table of a number.

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Rebol Celsius to Fahrenheit

c: 25
f: (c * 9 / 5) + 32
print f

Converts Celsius to Fahrenheit.

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Rebol Simple Alarm Simulation

temp: 80
thresh: 75
print either temp > thresh ["Alarm: Temperature Too High!"] ["Temperature Normal"]

Simulates an alarm when temperature exceeds a threshold.

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Rebol Random Walk Simulation

steps: 10
pos: 0
foreach i 1 2 3 4 5 6 7 8 9 10 [
    if random 1 < 0.5 [pos: pos + 1] [pos: pos - 1]
    print pos
]

Simulates a 1D random walk.

Let’s Try →

Frequently Asked Questions about Rebol

What is Rebol?

What are the primary use cases for Rebol?

Network protocols and communication. Scripting and automation. Rapid prototyping of applications. Data exchange with custom dialects. Embedded or lightweight distributed applications

What are the strengths of Rebol?

What are the limitations of Rebol?

How can I practice Rebol typing speed?

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