Kotlin REPL and script mode - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Kotlin REPL?

Kotlin REPL is a Read-Eval-Print Loop. It lets you write and run Kotlin code line by line in an interactive way, like chatting with the computer.

beginner

How do you start Kotlin REPL from the command line?

You type kotlinc and press Enter. This opens the Kotlin REPL where you can type Kotlin code directly.

beginner

What is Kotlin script mode used for?

Kotlin script mode lets you write Kotlin code in a file with .kts extension and run it without compiling. It's good for quick tasks and automation.

beginner

How do you run a Kotlin script file named hello.kts?

You run kotlin hello.kts in the command line. This executes the script without creating a separate program.

intermediate

What is the main difference between Kotlin REPL and script mode?

REPL runs code interactively line by line, great for testing ideas quickly. Script mode runs a whole Kotlin file as a script, useful for small programs or automation.

What does REPL stand for in Kotlin?

A Run-Evaluate-Process Loop

B Run-Execute-Program Language

C Read-Eval-Print Loop

D Read-Edit-Print Language

REPL means Read-Eval-Print Loop, which lets you type code and see results immediately.

Which command starts the Kotlin REPL?

A kotlinc

B kotlin run

C kotlin script

D kotlinc -script

Typing kotlinc starts the Kotlin REPL for interactive coding.

What file extension is used for Kotlin script files?

A .kt

B .kotlin

C .script

D .kts

Kotlin scripts use the .kts extension.

How do you run a Kotlin script file named test.kts?

A kotlin test.kts

B kotlinc -script test.kts

C kotlinc test.kts

D kotlin -script test.kts

Use kotlin test.kts to run a Kotlin script file.

Which mode is best for quickly testing small pieces of Kotlin code?

A Script mode

B REPL

C Compiled mode

D Debug mode

REPL is best for quick, interactive testing of Kotlin code.

Explain how Kotlin REPL helps beginners learn Kotlin.

Think about how typing code line by line and seeing results helps learning.

Describe the steps to run a Kotlin script file from the command line.

Focus on the file type and the command used.

Practice

1. What is the main purpose of Kotlin REPL?

easy

A. To run Kotlin code interactively line by line

B. To compile Kotlin code into Java bytecode

C. To create Android applications

D. To manage Kotlin project dependencies

Solution

1. Step 1: Understand REPL meaning

   Kotlin REPL stands for Read-Eval-Print Loop, which runs code interactively.

2. Step 2: Identify REPL use

   It lets you type and run Kotlin code line by line without compiling a full program.

3. Final Answer:

   To run Kotlin code interactively line by line -> Option A

4. Quick Check:

   Kotlin REPL = Interactive code running [OK]

Hint: REPL runs code line by line interactively [OK]

Common Mistakes:

• Confusing REPL with full project compilation
• Thinking REPL is for app deployment
• Assuming REPL manages dependencies

2. Which file extension is used for Kotlin script files?

easy

A. .kts

B. .skr

C. .kotlin

D. .kt

Solution

1. Step 1: Recall Kotlin file types

   Kotlin source files usually use .kt extension for normal programs.

2. Step 2: Identify script file extension

   Kotlin scripts use .kts extension to run code without full compilation.

3. Final Answer:

   .kts -> Option A

4. Quick Check:

   Kotlin script files = .kts [OK]

Hint: Scripts use .kts extension, not .kt [OK]

Common Mistakes:

• Choosing .kt which is for normal Kotlin files
• Assuming .kotlin or .skr are valid extensions
• Mixing script files with compiled files

3. What is the output of this Kotlin REPL session?

val x = 5
val y = 10
x + y

medium

A. 510

B. Error: undefined variables

C. x + y

D. 15

Solution

1. Step 1: Evaluate variable assignments

   x is assigned 5, y is assigned 10 in REPL environment.

2. Step 2: Calculate expression result

   x + y equals 5 + 10 which is 15.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add values assigned to variables for output [OK]

Common Mistakes:

• Concatenating numbers as strings (510)
• Printing expression text instead of result
• Assuming variables are undefined in REPL

4. Identify the error in this Kotlin script file example.kts:

val name = "Alice"
println(Name)

medium

A. Script files cannot use println

B. Variable 'Name' is not defined (case sensitive)

C. Missing semicolon after println statement

D. String literals must use single quotes

Solution

1. Step 1: Check variable usage

   Variable declared as 'name' but used as 'Name' which differs in case.

2. Step 2: Understand Kotlin case sensitivity

   Kotlin variables are case sensitive, so 'Name' is undefined causing error.

3. Final Answer:

   Variable 'Name' is not defined (case sensitive) -> Option B

4. Quick Check:

   Variable names are case sensitive [OK]

Hint: Check variable name case carefully [OK]

Common Mistakes:

• Thinking semicolons are mandatory
• Believing println is disallowed in scripts
• Using single quotes for strings in Kotlin

5. You want to quickly test a Kotlin function without creating a full project. Which approach is best?

hard

A. Write the function in Java and call it from Kotlin

B. Create a full Kotlin project and add the function

C. Use Kotlin REPL to define and test the function interactively

D. Write the function in a .kts script file and run it

Solution

1. Step 1: Compare quick testing methods

   Creating a full project is slow; writing Java adds complexity.

2. Step 2: Choose between script and REPL

   REPL lets you define and test functions interactively without saving files.

3. Step 3: Understand REPL advantage

   REPL is fastest for quick tests; scripts require saving and running files.

4. Final Answer:

   Use Kotlin REPL to define and test the function interactively -> Option C

5. Quick Check:

   REPL = fastest interactive testing [OK]

Hint: Use REPL for fastest interactive function testing [OK]

Common Mistakes:

• Assuming scripts are faster than REPL
• Thinking full projects are needed for tests
• Confusing Java code with Kotlin quick tests