REPL Interactive Interpreter

YaoXiang REPL (Read-Eval-Print Loop) is an interactive code execution environment that allows you to input and execute YaoXiang code line by line, making it ideal for learning, testing, and debugging.

Quick Start

Starting the REPL

Run the following command in the terminal to start the REPL:

yx repl

Or simply run yaoxiang (without any subcommand):

yaoxiang

After starting, you will see the prompt:

YaoXiang REPL - Type :help for assistance
Press Ctrl+D or :quit to exit

>>

Basic Usage

Enter YaoXiang code after the >> prompt and press Enter to execute:

>> 1 + 2
3

>> "Hello, World!"
"Hello, World!"

>> x = 10
>> x * 2
20

Exiting the REPL

There are three ways to exit the REPL:

1. Keyboard shortcut: Press Ctrl+D
2. Command: Enter :quit or :q
3. Interrupt: Press Ctrl+C to interrupt the current input

Command System

The REPL provides a series of special commands starting with a colon :.

Help Command

>> :help

Displays help information for all available commands.

Quit Command

>> :quit

Exits the REPL. You can also use the short form :q.

Clear Command

>> :clear

Clears all defined variables and functions, resetting the REPL state. You can also use the short form :c.

Type Inspection Command

>> :type x

Inspects the type information of symbol x. You can also use the short form :t.

Example:

>> name = "YaoXiang"
>> :type name
name: String

>> add: (a: Int, b: Int) -> Int = a + b
>> :type add
add: fn(Int, Int) -> Int

Symbol List Command

>> :symbols

Lists all defined symbols (variables and functions) in the current REPL. You can also use the short forms :i or :info.

Example:

>> x = 10
>> y = 20
>> greet: (name: String) -> String = "Hello, " + name
>> :symbols
x: Int
y: Int
greet: fn(String) -> String

History Command

>> :history

Displays the command history. You can also use the short form :hist.

Statistics Command

>> :stats

Displays execution statistics, including the number of evaluations and total execution time.

Example:

>> :stats
Eval count: 5
Total time: 12.34ms

Code Execution

Expression Evaluation

The REPL can evaluate any valid YaoXiang expression:

>> 1 + 2
3

>> 10 * 5 + 3
53

>> "Hello" + " " + "World"
"Hello World"

>> true and false
false

Variable Definition

Define variables directly using the variable name:

>> name = "YaoXiang"
>> age = 25
>> pi = 3.14159

You can also explicitly annotate the type:

>> name: String = "YaoXiang"
>> age: Int = 25

After definition, variables can be used in subsequent code:

>> name
"YaoXiang"

>> age + 5
30

Function Definition

YaoXiang has no fn keyword; functions are simply values with signatures:

>> add: (a: Int, b: Int) -> Int = a + b
>> greet: (name: String) -> String = "Hello, " + name

Calling a function:

>> add(3, 4)
7

>> greet("World")
"Hello World"

Multi-line Code

The REPL supports multi-line code input. When it detects incomplete code (such as unclosed parentheses), it automatically enters continuation mode:

>> factorial: (n: Int) -> Int = {
..     if n <= 1 { return 1 }
..     return n * factorial(n - 1)
.. }

The continuation prompt is .., indicating that the REPL is currently in multi-line input mode.

Type Definition

>> Point: Type = { x: Float, y: Float }

Variant Type Definition (Enum)

>> Color: Type = { red: () -> Color, green: () -> Color, blue: () -> Color }

Auto-completion

The REPL provides intelligent auto-completion to help you input code quickly.

Trigger Method

Press the Tab key to trigger auto-completion.

Completion Content

1. Keyword completion: YaoXiang language keywords (press Tab to expand)
2. Symbol completion: Already defined variable and function names
3. Builtin function completion: Builtin functions such as print, len, range, typeof, assert, etc.

Completion Examples

>> my_variable = 42
>> my_<Tab>
my_variable: Int

>> calculate_sum: (a: Int, b: Int) -> Int = a + b
>> calc<Tab>
calculate_sum: fn(Int, Int) -> Int

Advanced Features

Error Handling

When an error occurs in the code, the REPL displays detailed error information:

>> x = 10 / 0
Error: Runtime error: DivisionByZero

>> undefined_variable
Error: Unknown symbol: undefined_variable

Errors do not terminate the REPL session; you can continue entering new code.

History

The REPL automatically saves command history, supporting:

• Up/Down arrows: Browse through command history
• Search: Enter a partial string and use the up/down arrows to search
• History file: History is saved to a file and automatically loaded on the next startup

Execution Statistics

Use the :stats command to view execution statistics:

>> :stats
Eval count: 15
Total time: 45.67ms

This helps monitor code performance.

Best Practices

1. Use Meaningful Variable Names

// Good
user_name = "YaoXiang"
max_retries = 3

// Bad
x = "YaoXiang"
n = 3

2. Define Functions to Reuse Code

>> is_even: (n: Int) -> Bool = n % 2 == 0
>> is_even(4)
true
>> is_even(7)
false

3. Use :clear to Reset State

When the REPL state becomes messy, use :clear to reset:

>> :clear
Context cleared

4. Leverage Auto-completion for Efficiency

Enter the first few characters and press Tab to quickly complete variable and function names.

5. Use Multi-line Input for Complex Code

>> fibonacci: (n: Int) -> Int = {
..     if n <= 1 { return n }
..     return fibonacci(n - 1) + fibonacci(n - 2)
.. }

FAQ

Q: How do I view the definition of a function?

A: Use the :type command to view the function signature:

>> :type my_function
my_function: fn(Int, String) -> Bool

Q: How do I clear all definitions?

A: Use the :clear command:

>> :clear

Q: Why isn't my multi-line code executing?

A: Check for unclosed parentheses, quotes, or braces. The REPL waits for complete code input.

Q: How do I interrupt long-running code?

A: Press Ctrl+C to interrupt the current execution.

Q: What data types does the REPL support?

A: The REPL supports all YaoXiang data types:

• Int: Integer
• Float: Floating-point number
• String: String
• Bool: Boolean
• Void: Void type
• Custom record types and variant types

Example Session

Here is a complete example of a REPL session:

YaoXiang REPL - Type :help for assistance
Press Ctrl+D or :quit to exit

>> greeting = "Hello"
>> name = "YaoXiang"
>> greeting + ", " + name + "!"
"Hello, YaoXiang!"

>> factorial: (n: Int) -> Int = {
..     if n <= 1 { return 1 }
..     return n * factorial(n - 1)
.. }
..
>> factorial(5)
120

>> :symbols
greeting: String
name: String
factorial: fn(Int) -> Int

>> :stats
Eval count: 4
Total time: 2.34ms

>> :quit

Related Commands

Command	Short Form	Function
:help	:h	Display help information
:quit	:q	Exit the REPL
:clear	:c	Clear all state
:type	:t	View symbol type
:symbols	:i	List all symbols
:history	:hist	Display command history
:stats	-	Display execution stats