Language-Specific REPL Behavior¶

Different languages have different REPL behaviors. This guide explains how each language handles sessions.

Python¶

Python accumulates code in a temporary module:

python>>> x = 10
python>>> def greet(name): return f"Hello, {name}"
python>>> import math

All persist across commands.

Expressions automatically print their repr():

python>>> 2 + 2
4

python>>> [1, 2, 3]
[1, 2, 3]

python>>> "hello".upper()
'HELLO'

Statements don't print:

python>>> x = 10
# No output

python>>> if True: print("yes")
yes

Use ... for continuation:

python>>> def factorial(n):
...     if n <= 1:
...         return 1
...     return n * factorial(n-1)

python>>> factorial(5)
120

Variables and functions persist:

javascript>>> let count = 0

javascript>>> function increment() { count++; return count; }

javascript>>> increment()
1

javascript>>> increment()
2

Last expression is returned:

javascript>>> 2 + 2
4

javascript>>> [1, 2, 3].map(x => x * 2)
[ 2, 4, 6 ]

Rust compiles snippets incrementally:

rust>>> let mut x = 10;

rust>>> x += 5;

rust>>> x
15

Rust automatically wraps code in main():

rust>>> println!("Hello");
# Wrapped: fn main() { println!("Hello"); }

Each snippet is compiled, so errors are caught:

rust>>> let x: i32 = "hello";
error[E0308]: mismatched types

Go maintains state across commands:

go>>> x := 10

go>>> y := 20

go>>> x + y
30

Automatically includes package main:

go>>> import "fmt"

go>>> fmt.Println("Hello")
Hello

Variables and functions persist:

bash>>> NAME="Alice"

bash>>> greeting() { echo "Hello, $1"; }

bash>>> greeting $NAME
Hello, Alice

Session script is rewritten on each evaluation.

Code snippets are accumulated:

c>>> #include <stdio.h>

c>>> int x = 10;

c>>> printf("%d\n", x);
10

Compiled on each command:

c>>> int y = "hello";
error: incompatible types

# Use help()
python>>> help(str.split)

# Check type
python>>> type([1, 2, 3])
<class 'list'>

# List attributes
python>>> dir({})

# Check prototype
javascript>>> Object.getPrototypeOf([])

# Type checking
javascript>>> typeof 42
'number'

# Type annotation
rust>>> let x: i32 = 10;

# Explicit mut
rust>>> let mut count = 0;