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Contents
require 'binding_of_caller'
class Mercury
class Cps
# Syntactic sugar for and_then chains.
def self.seql(depth=1, &block)
# EXPERIMENTAL
# The trick here is to execute the block in a context where
# 1. we can simulate local let-bound variables, and
# 2. the block can access variables and methods available
# outside the call to seql.
#
# To achieve this, we instance_exec the block in a SeqWithLet
# object, which provides the let bound variables (as methods)
# and uses method_missing to proxy other methods to the parent
# binding.
#
# Note: parent instance variables are not available inside the block.
# Note: keyword arguments are not proxied to methods called in the parent binding
context = SeqWithLet.new(binding.of_caller(depth))
context.instance_exec(&block)
context.__chain
end
class SeqWithLet
def and_then(&block)
@__chain = __chain.and_then(&block)
end
def and_lift(&block)
@__chain = __chain.and_lift(&block)
end
def let(name, &block)
and_then(&block)
and_then do |value|
__values[name] = value
Cps.lift{value}
end
end
def initialize(parent_binding)
@__parent_binding = parent_binding
end
def __chain
@__chain ||= Cps.identity
end
def method_missing(name, *args, &block)
__values.fetch(name) { __parent_call(name.to_s, *args, &block) }
end
def __parent_call(name, *args, &block)
@__parent_caller ||= @__parent_binding.eval <<-EOD
proc do |name, *args, &block|
send(name, *args, &block)
end
EOD
@__parent_caller.call(name, *args, &block)
end
def __values
@__values ||= {}
end
end
end
end
Version data entries
12 entries across 12 versions & 1 rubygems