blocks

# Blocks and closures: code you hand to a function.

# `yield` runs the block the caller passed.
def repeat(times : Int32)
  times.times { |i| yield i }
end

repeat(3) { |i| puts "step #{i}" }

# A block sees the variables around it.
total = 0
[1, 2, 3].each { |n| total += n }
puts total

# `->` makes a function value you can store and call later.
square = ->(x : Int32) { x * x }
puts square.call(7)

# It captures its surroundings too: this one counts every call.
count = 0
tick = ->() { count += 1 }
tick.call
tick.call
puts count

# A block parameter with a type, handed on as a value.
def apply(x : Int32, &f : Int32 -> Int32) : Int32
  f.call(x)
end

puts apply(5) { |v| v + 100 }