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(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.

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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.

I would be very in favour of making λ a keyword, though. Maybe a linter could convert \ to λ.

it would be confusing since it's not part of UnicodeSyntax

https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/unic...

Well, even better to add it to that! But I was thinking generally, to be honest. I really want Python to synonimise the keyword lamdba with the λ symbol so I can golf my Advent of Code code better.

Argh. Synonymise.

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

Well if you're going to eat crow, I may as well eat pigeon, for I didn't realise that paper wasn't showing real source.

Thanks for the link to the LCF text though :^)

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