Issue #15428 has been updated by Dan0042 (Daniel DeLorme). Maybe it was already obvious to everyone, but I feel that something important has not been mentioned in this discussion: `(a >> b).call(x)` is equivalent to `b.call(a.call(x))` but **neither a nor b needs to be a Proc**. Either could be a Method, for example. So coercing the argument to Proc is neither needed nor desirable. In the same way that `"" + 2` is a TypeError because `2` is not implicitly converted, `myproc >> :symbol` is a TypeError because `:symbol` is not implicitly converted. That's fully consistent with Ruby as a strongly typed language. I think the proper solution here is `JSON.:parse >> .:symbolize_keys` ... we need to resurrect #12125 and #16264 but with better syntax and a more complete picture around FP. ---------------------------------------- Bug #15428: Refactor Proc#>> and #<< https://bugs.ruby-lang.org/issues/15428#change-103571 * Author: zverok (Victor Shepelev) * Status: Open * Priority: Normal * Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN ---------------------------------------- #6284 introduced `Proc#>>` and `Proc#<<`, but the requirements to the argument is totally inconsistent with ANY other place in Ruby. Currently, it is the **only** place in Ruby where coercing argument to `Proc` is done with `#call` method. Everywhere else it is done with `#to_proc`, and `#call` method never had any special significance except for `.()` sugar. I believe there are two possible actions: 1. change `#>>` and `#<<` to use `#to_proc` (which will give Symbols composability for free), **or, alternatively** 2. state that `#call` from now on has a special meaning in Ruby and probably decide on other APIs that should respect it (for example, auto-define `#to_proc` on any object that has `#call`) Either is OK, the current situation is not. PS: One more problem (that probably should be discussed separately) is that check for `#call` existence is performed pretty late, which can lead to this kind of errors: ```ruby # At code loading time: # I erroneously thought this is correct. It is not, but the line would perform without # any error. PROCESSOR = JSON.method(:parse) >> :symbolize_keys # Later, in runtime: '{"foo": "bar"}'.then(&PROCESSOR) # NoMethodError (undefined method `call' for :symbolize_keys:Symbol) ``` **UPD 2018-12-29:** As this ticket was ignored prior to 2.6 release, I rewrote it in an "actionable" instead of "question" manner. -- https://bugs.ruby-lang.org/