lambdas_and_blocks.rb

# Lambdas, Proc.new, and Blocks - Bitmaker breakout session
# Friday March 8, 2013

## LAMBDAS

# Basic Usage:
# Think of lambdas as methods that have no name and instead they can be assigned to a variable and thus be passed around.
l = lambda {"do or do not"}
puts l.call   # returns => do or do not

### DO-MATH EXAMPLE (WITH A LAMBDA) ###

# Below is a generic math function which accepts 2 numbers and a math function
# This function "calls" the math lambda, passing num1 and num2 as inputs to the lambda.
# It does not know or care about what math does, just that it is a lambda that it can "call"

def do_math(num1, num2, math)  
  math.call(num1, num2)  
end

# Now let's use the do_math method, passing 2, 3, and an `adder` function
adder = lambda {|num1, num2| num1 + num2} # adds two numbers and returns the result
result = do_math(2, 3, adder)  
puts result

# We could just pass the lambda right into do_math instead of assigning it to the adder variable first:
result = do_math(2, 3, lambda {|num1, num2| num1 + num2})
puts result

## Consider lambdas and Proc.new the SAME (for the time being). So this will give us the same behavior and result:
result = do_math(2, 3, Proc.new {|num1, num2| num1 + num2})
puts result

## BLOCKS
# Think of blocks as in-line, single-use versions of lambdas

### DO-MATH EXAMPLE (WITH A BLOCK) ###

# Note how the method do_math2 below does NOT mention that it accepts or expects a block.
# Any method can be passed a block (of code); whereas lambdas need to be passed in as normal arguments like num1 and num2

def do_math2(num1, num2)
  yield(num1, num2)  ### yield is similar to .call except used to call the block.
end

result = do_math2(2,3) { |num1, num2| num1 + num2 }
puts result

## This can also be re-written as:

result = do_math2(2,3) do |num1, num2| 
  num1 + num2
end
puts result

## This is called Functional programming, where CODE is also passed around instead of just DATA.
## If this is still unclear, that's okay. It is one of the more complicated parts of Ruby and usually takes time to sink in.