Skip to main content

Error Class

Error is Alia's built-in error class, used to represent and handle error information in programs.

Creating Errors​

Using the Constructor​

The constructor accepts (message, name, cause) by position, and array-style calls pass arguments in the order of the formal parameters.

const cause = new Error ['Cause']
const err1 = new Error ['Something went wrong']
const err2 = new Error ['Error message', 'CustomError']
const err3 = new Error ['Error message', 'CustomError', cause]

Instance Properties​

message​

The error's descriptive message.

const err = new Error ['Invalid input']
print err.message  ~ outputs 'Invalid input'

name​

The error's name/type.

const err = new Error ['Error', 'TypeError']
print err.name  ~ outputs 'TypeError'

cause​

The error's underlying cause. Defaults to Null.

const originalError = new Error ['Original error']
const wrappedError = new Error ['Wrapped error', 'Error', originalError]
print wrappedError.cause  ~ outputs the original error object

stack​

The error's stack information. Taken from the cause's stack; Null when there is no cause.

const err = new Error ['Error occurred']
print err.stack  ~ outputs null

Instance Methods​

toString​

Converts the error to its string representation. Zero-argument methods are invoked via call, returning a String of the form Error <name>: <message>.

const err = new Error ['Invalid input', 'TypeError']
print call err.toString  ~ outputs 'Error TypeError: Invalid input'

valueOf​

Returns the error's message content. Zero-argument methods are invoked via call.

const err = new Error ['Invalid input']
print call err.valueOf  ~ outputs 'Invalid input'

Error Handling​

throw Statement​

Throws an error:

throw new Error ['Something went wrong']
throw new Error ['Invalid type', 'TypeError']

try-catch Statement​

Catches and handles errors:

try {
  throw new Error ['Error occurred']
} catch err {
  print 'Caught error: ' .. (call err.toString)
}

Error Type Examples​

Custom Error Types​

const typeError = new Error ['Expected a number', 'TypeError']
const rangeError = new Error ['Value out of range', 'RangeError']
const validationError = new Error ['Invalid input', 'ValidationError']

Error Chains​

const rootCause = new Error ['Database connection failed']
const serviceError = new Error ['Service unavailable', 'ServiceError', rootCause]
const apiError = new Error ['API request failed', 'APIError', serviceError]
print 'API error cause: ' .. (call apiError.cause.toString)

Example Code​

const simpleError = new Error ['Simple error']
const namedError = new Error ['Named error', 'CustomError']
print 'Simple error: ' .. (call simpleError.toString)
print 'Named error: ' .. (call namedError.toString)
print 'Error message: ' .. namedError.message
print 'Error name: ' .. namedError.name
try {
  throw new Error ['Thrown error']
} catch err {
  print 'Caught error: ' .. (call err.toString)
}
alias validateInput <String input> -> {
  if input.length == 0 {
    throw new Error ['Input cannot be empty', 'ValidationError']
  }
  true
}
try {
  validateInput ''
} catch err {
  if err.name == 'ValidationError' {
    print 'Validation error: ' .. err.message
  } else {
    print 'Other error: ' .. (call err.toString)
  }
}
const original = new Error ['Root cause']
const wrapped = new Error ['Wrapped error', 'WrappedError', original]
print 'Outer error: ' .. (call wrapped.toString)
if Ok wrapped.cause {
  print 'Inner cause: ' .. (call wrapped.cause.toString)
}
try {
  const value = -1
  if value < 0 {
    throw new Error ['Value must be positive', 'RangeError']
  }
} catch err {
  switch err.name {
    case 'RangeError' {
      print 'Range error: ' .. err.message
    }
    case 'TypeError' {
      print 'Type error: ' .. err.message
    }
    default {
      print 'Unknown error: ' .. (call err.toString)
    }
  }
}

Next Steps​