Module: Deterministic::Monad

Included in:
Option, Result
Defined in:
lib/deterministic/monad.rb

Defined Under Namespace

Classes: NotMonadError

Instance Method Summary collapse

Instance Method Details

#==(other) ⇒ Object

Two monads are equivalent if they are of the same type and when their values are equal



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# File 'lib/deterministic/monad.rb', line 51

def ==(other)
  return false unless other.is_a? self.class
  @value == other.instance_variable_get(:@value)
end

#bind(proc = nil, &block) ⇒ Object Also known as: >>=

The monad: takes a function which returns a monad (of the same type), applies the function

bind

(a -> Mb) -> M a -> M b

the self.class, i.e. the containing monad is passed as a second (optional) arg to the function



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# File 'lib/deterministic/monad.rb', line 27

def bind(proc=nil, &block)
  (proc || block).call(value).tap do |result|
    parent = self.class.superclass === Object ? self.class : self.class.superclass
    raise NotMonadError, "Expected #{result.inspect} to be an #{parent}" unless result.is_a? parent
  end
end

#fmap(proc = nil, &block) ⇒ Object

The functor: takes a function (a -> b) and applies it to the inner value of the monad (Ma), boxes it back to the same monad (Mb)

fmap

(a -> b) -> M a -> M b



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# File 'lib/deterministic/monad.rb', line 19

def fmap(proc=nil, &block)
  result = (proc || block).call(value)
  self.class.new(result)
end

#initialize(value) ⇒ Object 



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# File 'lib/deterministic/monad.rb', line 5

def initialize(value)
  @value = join(value)
end

#inspect ⇒ Object

Return the string representation of the Monad



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# File 'lib/deterministic/monad.rb', line 57

def inspect
  name = self.class.name.split("::")[-1]
  "#{name}(#{value})"
end

#join(value) ⇒ Object

If the passed value is monad already, get the value to avoid nesting M[M] is equivalent to M



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# File 'lib/deterministic/monad.rb', line 11

def join(value)
  if value.is_a? self.class then value.value
  else value end
end

#to_s ⇒ Object 



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# File 'lib/deterministic/monad.rb', line 41

def to_s
  value.to_s
end

#value ⇒ Object

Get the underlying value, return in Haskell

return

M a -> a



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# File 'lib/deterministic/monad.rb', line 37

def value
  @value
end