Errors and results

OSL has thrown errors for exceptional control flow and result values for operations where failure is part of the API.

Throwing

if config == null (
  throw "Missing configuration"
)

A thrown value stops the current operation unless a catch expression handles it.

Catch expressions

object data = schema.safeParse(input) catch (
  log _.unwrapErr().message
  return {}
)

Inside the catch block, _ is the failed result or error value supplied by the expression. A catch block returns its replacement value with return.

Result values

Import std:result when constructing result values directly:

import "std:result"

def divide(number left, number right) result<number, string> (
  if right == 0 return result.err("division by zero")
  return result.ok(left / right)
)

Inspect and unwrap the result:

result<number, string> calculated = divide(10, 2)

if calculated.isErr() (
  log calculated.unwrapErr()
  return
)

number value = calculated.unwrap()

unwrap() and unwrapErr() fail when called on the wrong variant. Use unwrapAs(type) when a dynamic success value needs an assertion.

Assertions are runtime checks

.assert(type) is also a failure boundary:

object payload = decoded.assert(object)

Use .assertElse(...) when a fallback is valid. Do not use it to hide malformed required data. The OriginChats server validates protocol input with schemas, then uses .assert(...) after validation has established the type.

Process exits

The language command exit status terminates the process. The std:process package also provides process.exit(status).

if invalidConfig (
  log "Invalid configuration"
  exit 1
)

osl run returns the program's exit status to the shell.