Class: TAlgebra::Monad::Maybe

Inherits:
Object
  • Object
show all
Includes:
SingleValued
Defined in:
lib/t_algebra/monad/maybe.rb

Constant Summary collapse

NOTHING = 
:nothing
JUST = 
:just

Class Method Summary collapse

Instance Method Summary collapse

Methods included from SingleValued

included

Class Method Details

.nothing ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 15

def nothing
  new(is: NOTHING)
end

.pure(value) ⇒ Object Also known as: just 



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# File 'lib/t_algebra/monad/maybe.rb', line 10

def pure(value)
  new(is: JUST, value: value)
end

.to_maybe(value_or_nil) ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 19

def to_maybe(value_or_nil)
  value_or_nil.nil? ? nothing : pure(value_or_nil)
end

Instance Method Details

#==(other) ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 60

def ==(other)
  to_obj == other.to_obj
end

#bind {|value| ... } ⇒ Object

Yields:

  • (value) 


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# File 'lib/t_algebra/monad/maybe.rb', line 29

def bind(&block)
  return dup if nothing? || !block
  yield value
end

#fetch(key) ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 52

def fetch(key)
  bind do |o|
    self.class.to_maybe(
      o.respond_to?(:[]) ? o[key] : o.send(key)
    )
  end
end

#fmap(&block) ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 24

def fmap(&block)
  return dup if nothing? || !block
  self.class.just(yield(value))
end

#from_maybe ⇒ Object

Raises:



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# File 'lib/t_algebra/monad/maybe.rb', line 46

def from_maybe
  raise UseError.new("#from_maybe called without block") unless block_given?
  return yield if nothing?
  value
end

#from_maybe! ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 42

def from_maybe!
  from_maybe { |e| raise UnsafeError.new("#from_maybe! exception. #{e}") }
end

#just? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/t_algebra/monad/maybe.rb', line 38

def just?
  is == JUST
end

#nothing? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/t_algebra/monad/maybe.rb', line 34

def nothing?
  is == NOTHING
end

#to_obj ⇒ Object 



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# File 'lib/t_algebra/monad/maybe.rb', line 64

def to_obj
  {is.to_s => value, :class => self.class.name}
end