All the syntaxes I can think of offhand for lambdas / blocks

lambda_syntaxes.rb

# -----  Lambda  -----
# the syntax for a lambda: stabby arrow
-> a { a + a }


# -----  Block  -----
# the two literal syntaxes for a block, + syntax to place lambda into block slot
lambda { |a| a + a }
lambda do |a| a + a end
lambda &->(a) { a + a }


# -----  Parens are optional  -----
->(a) { a + a }

lambda() { |a| a + a }

lambda() do |a|
  a + a
end

l = ->(a) { a + a }
lambda(&l)


# -----  Lambda with both block literal syntaxes  -----
-> a { a + a }
-> a do
  a + a
end