resonad's Introduction

Resonad

Usage example (assume each method returns a Resonad):

find_widget(widget_id)
  .and_then { |widget| update_widget(widget) }
  .on_success { |widget| logger.info("Updated #{widget}" }
  .on_failure { |error| logger.warn("Widget update failed because #{error}") }

Success type:

result = Resonad.Success(5)
result.success? #=> true
result.failure? #=> false
result.value #=> 5
result.error #=> raises an exception

Failure type:

result = Resonad.Failure(:buzz)
result.success? #=> false
result.failure? #=> true
result.value #=> raises an exception
result.error #=> :buzz

Mapping monads:

result = Resonad.Success(5)
  .map { |i| i + 1 }
  .map { |i| i + 1 }
  .map { |i| i + 1 }
result.success? #=> true
result.value #=> 8

result = Resonad.Failure(:buzz)
  .map { |i| i + 1 }
  .map { |i| i + 1 }
  .map { |i| i + 1 }
result.success? #=> false
result.error #=> :buzz

Flat mapping monads (a.k.a. and_then):

result = Resonad.Success(5)
  .and_then { |i| Resonad.Success(i + 1) }
  .and_then { |i| Resonad.Failure("buzz #{i}") }
  .and_then { |i| Resonad.Success(i + 1) }
  .error #=> "buzz 6"

# can also use the less-nice `flat_map` method
result
  .flat_map { |i| Resonad.Success(i + 1) }

Automatic exception rescuing:

def try_divide(top, bottom)
  Resonad.rescuing_from(ZeroDivisionError) { top / bottom }
end

yep = try_divide(6, 2)
yep.success? #=> true
yep.value #=> 3

nope = try_divide(6, 0)
nope.success? #=> false
node.error #=> #<ZeroDivisionError: ZeroDivisionError>

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