RAA - merlin-let

Lisp/Scheme-like let mixin for IO, Hash and ENV.

io.let(io) { |io| block } - Reopens the IO object with the parameter, executes the block and then restores the IO object.
require 'merlin/let'
STDERR.let(STDOUT) { |stderr| STDERR.puts "to STDOUT" }

hash|ENV.let(array) { |array| block } - Reassigns the specified entries in the Hash to the specified values, executes the block and then restores the Hash.
require 'merlin/let'
ENV.let(['PATH', '/bin']) { |orig| system "echo" }