Comment by vosper | Hacker News Reader

Comment by vosper | Hacker News Reader

> Egison is a programming language that realizes non-linear pattern-matching against non-free data types.

It's a what? Can someone ELI5 this for a lowly Python and JS dev - why would I want this?

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I watched a talk about Scala's future [0] recently, in which the presenter compared the taglines of a few different languages (Go, Rust, Erlang, Scala), and how they relate to business pains or non-academic problems.

His conclusion about Scala's tagline - "Scala combines object-oriented and functional programming in one concise, high-level language" is that "no engineering manager in the history of software development ever thought to themselves 'hmmm, if only I had a language that fused OO and FP, I'd be able to solve my business problems'. That hasn't happened; that will never happen. This is an academic novelty that has zero relevance to any of us as professional software developers [...] this is not a business pain, this is an academic interest."

I felt a little bit like that when I read Egison's tagline: why should I care about this language?

[0] "The Last Hope for Scala's Infinity War" https://youtu.be/v8IQ-X2HkGE?t=15m8s

> It's a what? Can someone ELI5 this for a lowly Python and JS dev - why would I want this?

Nah, but I can ELI a person with some programming experience.

Pattern matching is super useful for writing code that spends a lot of time building and deconstructing syntactic data structures.

Non-linear pattern matching is useful when de-constructing large-ish expressions that might contain multiple occurances of the same sub-term.

Nonfree datatypes allow you to encode some constraints about your datatypes; e.g., "lists that are equal modulo permutation".

Supporting type-checked non-linear matching over nonfree datatypes allows you to encode a lot of constraints in the type system and syntax that would otherwise be encoded with lots of nested if-statements and only checked by tests, not by static type checking.

This combination of features could be very useful when implementing a lot of mathematical code that operates over algebraic structures. Which is why the language's homepage mentions the implementation of (features for) computer algebra systems as a sort of killer app.

> this is not a business pain, this is an academic interest

Not all innovation is motivated by the business pains of today's engineering managers. And often the solutions to those pains are not recognizable; e.g., thousands engineering manager in 1950 could've beneifted from CAD software but I bet very feew were sitting around saying "I could really use a good piece of CAD software right now".

Scala is another good example of that, despite a marketing complaints about messaging. No one asked for FP+OO, but Scala took off because the combination of FP and OO solved a lot of the pain caused by Java.

Substantially improving the ease of implementing new types of computer algebra systems could easily create a lot of business opportunities e.g. in providing improved analysis/synthesis tools for all sorts of CAD tools.

that said, I don't think this language hits the target. See the hodge operator example...

Thanks for making the effort to explain, I think I have a better handle on what it means now.

Scala's mistake is ostensibly that it is an academic language trying to pitch itself as a language for building business applications.

Egison appears to be a self-consciously academic language, which strikes me as a perfectly legitimate.

In particular, the goal seems to be to provide a more intuitive way of writing algorithms using extensible pattern matching. Now, I have worked on commercial software that has highly algorithmic parts (graph traversals, etc.) written in Erlang (a language that supports a powerful, but not extensible, form of pattern matching). I found the pattern matching facilities to be quite helpful in producing readable, concise, correct code.

The use case is narrow, but strikes me as real nonetheless.

> "Scala's mistake is ostensibly that it is an academic language trying to pitch itself as a language for building business applications."

It's a bit subtler than that. Scala is an industry programming language perfectly suited to business applications, but with a big academic and research input (remember that Odersky, its creator, was a big contributor to Java, an industry language) and with an initial emphasis on research. The mentioned talk is criticizing Scala's marketing blurb because it was written almost entirely from a research angle, and doesn't accurately and convincingly portray Scala's benefits for business. See the revised blurb at the end of the talk [1]. It's a question of being clever about marketing.

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[1] revised blurb: "Scala is an open source programming language that helps you write correct code and modify code safely, while seamlessly reusing existing JVM libraries."

As a Scala dev, one issue I see with the language is that it doesn't keep you in check. Easy things are easy and there are lots of syntax sugar and little conveniences here and there that make the language great, but the advanced features are just as accesible to the developer. You need self-restraint when doing Scala, there is a real risk of losing perspective and getting distracted with fancy features and libraries.

It requires taste or code reviews, essentially.

I have the same feeling. It is a very powerful and interesting language from my anecdotal experience, but I also feel it gives too much options to use

Which syntax sugar do you think verbose? I don't think Egison has lots of syntax sugar.

Which syntax sugar do you think verbose? I don't think Egison has lots of syntax sugar.

Egison features a customizable pattern-matching facility. Pattern-matching methods for each data type and pattern can be customizable by users. There might be a possibility that you thought syntax sugar is not syntax sugar.

I think you're right - this is an academic language. That doesn't mean it's devoid of value, it's just not meant to solve industrial problems. Instead, it's supposed to experiment with a new paradigm so that other (more pragmatic) languages can someday incorporate some of its ideas.

Scala has always nurtured that ridiculous notion that an animal that's 50% cat and 50% dog would appeal to both cat-lovers and dog-lovers, which doesn't actually make any sense.

This language is clearly an academic endeavor.

Disclaimer: I don't know what non-linear pattern matching on non-free data means either, but the fact that it's not explained to me is proof enough they aren't meaning to cater to non-academic users.

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