It's definitely the most influential of the statically typed functional languages. All other statically typed functional languages or libraries inherit a lot from Haskell implementations, type system and type class concepts.
Standard ML is more influential because it's the foundational statically typed functional language. But Haskell has gained more popularity with the general programming public, not just academics.
What modern language in use today was influenced by Haskell other than maybe Idris?
(To be clear, I am mot necessarily down on Haskell or what part it has played. It’s just that many languages seem to be stealing ideas from the languages I’ve listed more than Haskell, which was the criteria I had in mind.)
> This paper presents type classes, a new approach to ad-hoc polymorphism. Type classes permit overloading of arithmetic operators such as multiplication, and generalise the "eqtype variables" of Standard ML. Type classes extend the Hindley/Milner polymorphic type system ...
And it was my understanding that traits came more from the object-oriented world, such as Self and Smalltalk. Scala and Racket also had them before Rust, and Scala also has type classes.
Phil Wadler, the first author of the paper you cite, was literally a principal designer of Haskell. SML does not have type classes; your quote points out a deficiency in SML that motivates type classes.
My understanding is that "trait" is an unfortunately overloaded term. Traits in Rust are much more closely related to Haskell's type classes than to traits in the OOP sense.
> Phil Wadler, the first author of the paper you cite, was literally a principal designer of Haskell.
Yes, I know that. That's the point.
> SML does not have type classes; your quote points out a deficiency in SML that motivates type classes.
Again, that's the point. It's what "have an influence" means in that it was SML that influenced or inspired Haskell's type classes. And it's part of my overall point of SML being rather influential, although quietly.
> Traits in Rust are much more closely related to Haskell's type classes than to traits in the OOP sense.
I'm not so sure about that from what I have read. But I don't have enough information other than to just point to things I have read.
While I can't find any concrete information, I would be quite surprised if Rust's traits were influenced by type classes rather than the more OOP interpretation of traits (in the design space of traits vs mixins vs interfaces).
It showed that monads can be used to isolate I/O but have a very real cost when it comes to complexity, that laziness by default is a bad idea and that typeclasses are a good way to introduce ad hoc polymorphism.
Definitely a good result for a research language but far less ground-breaking than ML was (admittedly putting the bar very high).
The first language to implement type classes. The first language to structure computation with monads, which are now omnipresent in functional languages.