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Maybe Functor, Applicative and Monad

License: MIT License

Ruby 100.00%

ruby functor applicative monad

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bobjflong

ribimaybe's Issues

Push version 0.0.9 to Rubygems

Prove Maybe is a Functor

Alias #inspect to #to_s

[~]
% ruby --version
ruby 2.0.0p195 (2013-05-14 revision 40734) [x86_64-darwin13.0.0]
[~]
% irb
irb(main):001:0> require 'ribimaybe'
=> true
irb(main):002:0> include Ribimaybe::Maybe
=> Object
irb(main):003:0> Maybe(nil)
=> Ribimaybe::Maybe::Nothing
irb(main):004:0> puts Maybe(nil)
Nothing
=> nil
irb(main):005:0>

Prove Maybe is an Applicative Functor

pure id <*> v = v                            -- Identity
pure (.) <*> u <*> v <*> w = u <*> (v <*> w) -- Composition
pure f <*> pure x = pure (f x)               -- Homomorphism
u <*> pure y = pure ($ y) <*> u              -- Interchange

And the Functor instance should satisfy the following law:

fmap f x = pure f <*> x                      -- Fmap

Consider renaming rturn

It's unfortunate that return is a reserved keyword in Ruby and I worry that the ergonomics of #rturn are unsatisfactory.

Add terse operators for apply and bind

After receiving #22 I decided it would be nice if we could alias these methods to short binary operators, e.g. >>, >=.

Make case equality work as expected for Nothing

Return type for `Just#bind` insufficiently general

sorry for the terminology, I'm not familiar with the Contracts library

Just(1).bind{|x|
  Nothing.bind{|y|
    rturn(x+y)}}

should return Nothing. Instead:

Contract violation for return value: (ContractError)
    Expected: Ribimaybe::Maybe::Just,
    Actual: Ribimaybe::Maybe::Nothing
    Value guarded in: Ribimaybe::Maybe::Just::bind
    With Contract: Proc => Ribimaybe::Maybe::Just

Prove Maybe is a Monad

m >>= return     =  m                        -- right unit
return x >>= f   =  f x                      -- left unit

(m >>= f) >>= g  =  m >>= (\x -> f x >>= g)  -- associativity

mcfilib / ribimaybe Goto Github PK

ribimaybe's People

Contributors

Stargazers

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Forkers

ribimaybe's Issues

Push version 0.0.9 to Rubygems

Prove Maybe is a Functor

Alias #inspect to #to_s

Prove Maybe is an Applicative Functor

Consider renaming rturn

Add terse operators for apply and bind

Make case equality work as expected for Nothing

Return type for `Just#bind` insufficiently general

Prove Maybe is a Monad

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