Comment by Skinney
1 year ago
The syntax came from Elm, which got it’s syntax from Haskell (where Nix also got it from) which got its syntax from ML.
It’s a syntax that’s several decades old at this point.
It’s different, but not harder. If you learned ML first, you’d found Algol/C-like syntax equally strange.
(ETA: speaking strictly about anonymous functions; on rereading you might be talking about the absence of parens and commas for function application.)
That's not ML syntax. Haskell got it from Miranda, I guess?
In SML you use the `fn` keyword to create an anonymous function; in Ocaml, it's `fun` instead.
I believe the `\` character for functions is original to Haskell. Miranda does not have anonymous functions as a part of the language.
The \ is a simplified lambda, because most programmers can't type λ easily.
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Well, ML (or at least the first versions of it) used a λx • x syntax [1] for λ-abstractions, the same (excluding the use of • over .) notation as used with the Lambda Calculus, and I've always assumed \ was an ASCII stand in.
[1]: https://homepages.inf.ed.ac.uk/wadler/papers/papers-we-love/... (can be spotted on page 353)
That paper isn't showing real ML syntax itself; it's a mathematical presentation to demonstrate how the type system algorithm works. The actual original LCF/ML syntax would differ. I don't believe it used an actual lambda character, although for the life of me I can't find any evidence one way or another, not even in the LCF source code (https://github.com/theoremprover-museum/LCF77)
But yes, the slash is just an ASCII stand-in for a lambda.
ETA: I tracked down a copy of the Edinburgh LCF text and I have to eat crow. It doesn't use a lambda, but it does use a slash rather than a reserved word. The syntax, per page 22, is in fact, `\x. e`. Similar to Haskell's, but with a dot instead of an arrow.
https://archive.org/details/edinburghlcfmech0000gord
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