New EEP draft: Pinning operator ^ in patterns
Fri Dec 25 06:05:03 CET 2020
In Elixir syntax, with variables getting rebound in all source code it
makes sense that Elixir needs the pin operator ( ^ ) to say "Hey, this
is different, this isn't the imperative programming variable assignment
[match] you are accustom to!".
Erlang is different, with clearly immutable variable data. A consistent
variable name in the source code without a syntactic sugar ^ prefix
helps to prevent extra work changing unrelated source code in the future
as source code changes. The variable name is always referred to as the
same name in the same way, to refer to the same data. That sameness
helps developers understand the source code and adding a prefix would
obscure the variable name while attempting to communicate that matching
on a variable is somehow different from normal, though it is very normal
Matching is very important in Prolog too, with Erlang syntax being
naturally similar. A pin operator hasn't been necessary in Prolog
syntax, though the matching gets more complex in Prolog (solving rubik's
cubes with short examples and other amazing things). There isn't a clear
benefit to adding the Elixir pin operator to Erlang, just like there
wouldn't be a benefit to adding it to Prolog.
On 12/24/20 12:10 PM, Richard Carlsson wrote:
> 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.
> See also https://github.com/erlang/otp/pull/2951
> Ho ho ho,
> /Richard & the good folks at WhatsApp
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