Error Codes

Project Links: GitHub · VM Error Source

Overview

MaìLang uses the Result type for error handling and does not throw exceptions. Every fallible operation returns Result<T, E> or Option<T>.

Runtime Errors

VmError

Error code	Description	Example
StackOverflow	Stack overflow	Recursion too deep
StackUnderflow	Stack underflow	Pop from an empty stack
TypeError	Type error	"a" - 1
UndefinedVariable	Undefined variable	println(x)
UndefinedFunction	Undefined function	foo()
UndefinedProperty	Undefined property	obj.bar
WrongArgumentCount	Wrong argument count	add(1)
DivisionByZero	Division by zero	1 / 0
IndexOutOfBounds	Index out of bounds	arr[100]
InvalidOperation	Invalid operation	null + 1
RuntimeError	Runtime error	Generic error

CompilerError

Error code	Description
UndefinedVariable	Undefined variable
TooManyConstants	Too many constants (over 65536)
TooManyLocals	Too many locals (over 256)
TooManyUpvalues	Too many upvalues (over 256)
InvalidAssignmentTarget	Invalid assignment target
BreakOutsideLoop	break outside a loop
ContinueOutsideLoop	continue outside a loop
ReturnOutsideFunction	return outside a function
DuplicateFunction	Duplicate function name
DuplicateClass	Duplicate class name
DuplicateTrait	Duplicate trait name

ParseError

Error code	Description
UnexpectedToken	Unexpected token
UnexpectedEof	Unexpected end of file
InvalidExpression	Invalid expression
InvalidStatement	Invalid statement
ExpectedIdentifier	Expected identifier
ExpectedTypeAnnotation	Expected type annotation
ExpectedExpression	Expected expression
ExpectedPattern	Expected pattern
ExpectedBlock	Expected block
InvalidAssignmentTarget	Invalid assignment target
InvalidFunctionDefinition	Invalid function definition
InvalidClassDefinition	Invalid class definition
InvalidPattern	Invalid pattern

LexerError

Error code	Description
UnexpectedCharacter	Unexpected character
UnterminatedString	Unterminated string
UnterminatedChar	Unterminated char
InvalidEscapeSequence	Invalid escape sequence
InvalidNumber	Invalid number format
InvalidUnicodeEscape	Invalid Unicode escape

AnalyzerError

Error code	Description
UndefinedVariable	Undefined variable
UndefinedFunction	Undefined function
UndefinedClass	Undefined class
UndefinedTrait	Undefined trait
TypeMismatch	Type mismatch
ImmutableAssignment	Assignment to an immutable variable
ConstantAssignment	Assignment to a constant
WrongArgumentCount	Wrong argument count
MethodNotFound	Method not found
PropertyNotFound	Property not found
MissingTraitMethod	Unimplemented trait method
CircularInheritance	Circular inheritance
ThisOutsideMethod	this used outside a method
SuperOutsideSubclass	super used outside a subclass
DuplicateDefinition	Duplicate definition
UnusedVariable	Unused variable

Error Handling Best Practices

Handle errors with match

let result = match divide(10.0, 0.0) {
    Ok(v) => println("结果: {v}"),
    Err(e) => println("错误: {e}")
}

Use the ? operator

? is supported: it unwraps Ok/Some and early-returns Err/None from the current function.

fn process() -> Result<str, str> {
    let value = divide(10.0, 0.0)?  // early-return on error
    Ok("处理完成")
}

Custom error types

The enum keyword is not supported yet. For now, use string error codes or a class to carry error information:

fn do_something() -> Result<str, str> {
    // ...
    return Err("NotFound: file.txt")
}

Next Steps

• Type System — type details
• Operators — operator reference
• Built-in Functions — standard library functions