Smullyan

gem 'smullyan'

require 'smullyan'

# Using SKI combinator names
s = Smullyan::Birds::S
k = Smullyan::Birds::K  
i = Smullyan::Birds::I

# Or use the bird names!
kestrel = Smullyan::Birds::Kestrel      # K combinator
starling = Smullyan::Birds::Starling    # S combinator
mockingbird = Smullyan::Birds::Mockingbird # M combinator

# Example: Identity function derived from S and K
identity = s.(k).(k)
identity.(42) # => 42

# Example: Function composition with the Bluebird
bluebird = Smullyan::Birds::Bluebird
double = ->(x) { x * 2 }
increment = ->(x) { x + 1 }
double_after_increment = bluebird.(double).(increment)
double_after_increment.(5) # => 12

# Example: Y combinator for recursion
why = Smullyan::Birds::Why
factorial = why.(->(f) {
  ->(n) { n <= 1 ? 1 : n * f.(n - 1) }
})
factorial.(5) # => 120