<div dir="ltr">Sorry, I just did a quick hack instrumenting the compiler to emit the variable info, then built OTP from scratch using this.<br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><br> /Richard</div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Den fre 15 jan. 2021 kl 13:39 skrev Fernando Benavides <<a href="mailto:elbrujohalcon@gmail.com">elbrujohalcon@gmail.com</a>>:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_default" style="font-family:"trebuchet ms",sans-serif">Hey, Richard</div><div class="gmail_default" style="font-family:"trebuchet ms",sans-serif"><br></div><div class="gmail_default" style="font-family:"trebuchet ms",sans-serif">Do you mind sharing the code you used to analyze OTP's codebase? I would like to use it to analyze other large codebases as well :)</div><div class="gmail_default" style="font-family:"trebuchet ms",sans-serif"><br></div><div class="gmail_default" style="font-family:"trebuchet ms",sans-serif">Cheers!</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jan 15, 2021 at 1:34 PM Richard Carlsson <<a href="mailto:carlsson.richard@gmail.com" target="_blank">carlsson.richard@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>There have been many strong reactions in this thread, so let me give you some statistics to show how much this feature of using bound variables is actually used in practice. I checked the entire OTP codebase: there are just over 1300 modules, and in total about 595000 variable occurrences in patterns, of which only 3350 are already bound.. That makes 0.56% of all variables in patterns - about once in 200 to make it simple. On average, that's 2-3 usages per module - some modules using it more and some not using it at all.</div><div><br></div><div>I find it hard to see, then, why it should be a big issue to ask programmers to annotate these few occurrences for readability and maintainability. It's certainly not as big of a change as for example when the warning for unused variables, unless prefixed with _, was made the default.</div><div><br></div><div>Imagine a world where Erlang had not allowed already-bound variables in patterns (forcing you to use the idiom "X1 when X1 =:= X -> ...", as in e.g. Haskell), and that someone now came with the suggestion that to make things simpler, we could just implicitly match on the value of X if X is already bound. The old me from my university days would probably have said "that's really elegant, let's do it". But the maintainability-and-readability me, with experience of very large code bases, large numbers of developers, and many relative newcomers to the language, would say "aw hell no". This is a cute feature, but it carries a large cognitive cost and is not worth having compared to how relatively little it is used. Being explicit about intention is much more important.</div><div><br></div><div><div dir="ltr"> /Richard</div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Den tors 24 dec. 2020 kl 21:10 skrev Richard Carlsson <<a href="mailto:carlsson.richard@gmail.com" target="_blank">carlsson.richard@gmail.com</a>>:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">The ^ operator allows you to annotate already-bound pattern variables as ^X, like in Elixir. This is less error prone when code is being refactored and moved around so that variables previously new in a pattern may become bound, or vice versa, and makes it easier for the reader to see the intent of the code.<div><br></div><div>See also <a href="https://github.com/erlang/otp/pull/2951" target="_blank">https://github.com/erlang/otp/pull/2951</a><br clear="all"><div><div dir="ltr"><br></div><div>Ho ho ho,</div><div dir="ltr"><br> /Richard & the good folks at WhatsApp</div></div></div></div>
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