Kotlin REPL and script mode - Step-by-Step Execution

Concept Flow - Kotlin REPL and script mode

Start Kotlin REPL

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Type Kotlin code line

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REPL evaluates code

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Output result shown

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Type next line or exit

Back to Type Kotlin code line↓

Start Kotlin Script

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Write Kotlin code in file

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Run script with kotlin command

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Script executes top to bottom

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Output shown in console

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Script ends

↩Back to Type Kotlin code line

Kotlin REPL lets you type and run code line by line interactively. Script mode runs a whole Kotlin file from top to bottom.

Execution Sample

Kotlin

>>> val x = 5
>>> println(x * 2)

In REPL, define x as 5, then print x times 2, outputting 10.

Execution Table

Step	Input	Action	Output	State
1	val x = 5	Declare variable x with value 5	No output	x=5
2	println(x * 2)	Calculate x*2 and print	10	x=5
3	exit	Exit REPL session	Session ends	x=5

💡 User types exit to end REPL session

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	undefined	5	5	5

Key Moments - 2 Insights

Why does REPL show no output after declaring a variable?

Because variable declarations do not produce output themselves, only expressions like println() show output, as seen in step 1 and 2 of the execution_table.

How does script mode differ from REPL in running code?

Script mode runs the whole file top to bottom at once, unlike REPL which runs line by line interactively, as shown in the concept_flow diagram.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x after step 1?

A 10

B 5

C undefined

D 0

💡 Hint

Check the State column in row for step 1 in execution_table.

At which step does the REPL print output?

A Step 2

B Step 1

C Step 3

D No output at all

💡 Hint

Look at the Output column in execution_table rows.

If you run a Kotlin script file, how is the code executed?

A Line by line interactively

B Only the last line runs

C Top to bottom all at once

D Code does not run automatically

💡 Hint

Refer to the concept_flow description about script mode.

Concept Snapshot

Kotlin REPL lets you type and run code line by line interactively.
Variable declarations do not print output.
Use println() to see output.
Kotlin script mode runs a whole file top to bottom.
Run scripts with 'kotlin filename.kts'.
REPL is good for quick tests; scripts for full programs.

Full Transcript

This visual execution shows how Kotlin REPL and script mode work. In REPL, you start by typing code line by line. For example, declaring a variable x with value 5 does not print anything immediately. When you run println(x * 2), it calculates 10 and prints it. You can continue typing or exit the REPL. In script mode, you write Kotlin code in a file and run it all at once. The script executes from top to bottom and shows output in the console. This helps beginners see how interactive REPL differs from running a full script file.