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I'm waiting for pattern matching to be added to JS. The proposal[1] documents a lot of thought on how to add pattern matching to a language, including prior art

I'm waiting for pattern matching to be added to JS. The proposal[1] documents a lot of thought on how to add pattern matching to a language, including prior art in other languages. (Pattern matching was introduced to me via either F# or Erlang/Elixir.) DeltaScript pattern matching seems to be missing two major features; perhaps intentional because the implementation is more difficult: 1. Binding - useful to be able to assign variables to sub-parts of the control value. 2. Structural matching - matching based on the shape of the control value. I suppose both binding and structural matching can be accomplished with more verbose `passes` tests. (Also some redundant code to get the bindings; perhaps the `passes` test could return optional bindings.) [1]: https://github.com/tc39/proposal-pattern-matching https://github.com/tc39/proposal-pattern-matching

flinkerflitzer 2y ago
That's an interesting observation. Thanks for taking the time to think critically about my implementation. I posted about this on Reddit and someone pointed out something similar. I'll link that post for reference: https://www.reddit.com/r/ProgrammingLanguages/comments/1fb5yr6/switch_statements_function_pointerslambdas/ https://www.reddit.com/r/ProgrammingLanguages/comments/1fb5y... The gist (hehe) was that a full lambda expression in a `passes` case could often feel like overkill. This was the possible solution I suggested: What I could do is similar to what you suggested in another comment and similar to what C# does, where I add a third type of case that implicitly substitutes the control expression into a longer expression. Something like this, tentatively using the keyword `matches`: int x = rand(0, 11); when (x + 2) { matches _ < 5 || _ > 9 -> { /* body */ } } Here is a structural matching example: orientation(image img -> string) { when (img) { matches _.width == _.height -> return "square"; matches _.width > _.height -> return "landscape"; otherwise -> return "portrait"; } }

flinkerflitzer 2y ago

That's an interesting observation. Thanks for taking the time to think critically about my implementation. I posted about this on Reddit and someone pointed out something similar. I'll link that post for reference: https://www.reddit.com/r/ProgrammingLanguages/comments/1fb5yr6/switch_statements_function_pointerslambdas/ https://www.reddit.com/r/ProgrammingLanguages/comments/1fb5y... The gist (hehe) was that a full lambda expression in a `passes` case could often feel like overkill. This was the possible solution I suggested: What I could do is similar to what you suggested in another comment and similar to what C# does, where I add a third type of case that implicitly substitutes the control expression into a longer expression. Something like this, tentatively using the keyword `matches`: int x = rand(0, 11); when (x + 2) { matches _ < 5 || _ > 9 -> { /* body */ } } Here is a structural matching example: orientation(image img -> string) { when (img) { matches _.width == _.height -> return "square"; matches _.width > _.height -> return "landscape"; otherwise -> return "portrait"; } }