Here is an historical note for those who might be interested. In 1979 I did a Post-doc with Rod Burstall. I helped implement the programming language Hope, which was the first functional programming language to use pattern-matching in function definitions. The implementation was written in an older language called POP-2. Robin Milner and his group were at the the time working on LCF and ML, and they eventually incorporated Burstall's pattern ideas. Eventually, I recall there was a decision within the UK functional programming community to consolidate their efforts into what became Haskell. And of course we see how much Haskell has influenced the newest crop of imperative languages.
It is interesting (to me) to compare factorial in Rust with factorial in Hope:
Rust:
fn factorial(i: u64) -> u64 {
match I {
0 => 1,
n => n * factorial(n-1)
}
}
Hope:
dec factorial : num -> num;
--- factorial 0 <= 1;
--- factorial n <= n* factorial(n-1);
Note that, in Hope (unlike its own inspiration, Prolog, and, I think unlike Rust), the order of the rules does not matter: the most specific pattern takes precedence. Hope was primitive with respect to types, and did not use Milner's type inferrencing ideas. I don't think Burstall ever intended it to be a "real" programming language. When I left Edinburgh, Don Sanella took over from me, so I was not involved in writing the paper about Hope, but my contribution is acknowledged.
I implemented the pattern matching code, and the idea of pattern compilation occurred to me. I remember showing it to Rod. He freaked out at first, but after about a five minute harangue, the penny dropped, and I remember him saying "clever Michael", "clever Michael" in his charming way.
It is interesting (to me) to compare factorial in Rust with factorial in Hope:
Rust:
fn factorial(i: u64) -> u64 {
}Hope:
dec factorial : num -> num;
--- factorial 0 <= 1;
--- factorial n <= n* factorial(n-1);
Note that, in Hope (unlike its own inspiration, Prolog, and, I think unlike Rust), the order of the rules does not matter: the most specific pattern takes precedence. Hope was primitive with respect to types, and did not use Milner's type inferrencing ideas. I don't think Burstall ever intended it to be a "real" programming language. When I left Edinburgh, Don Sanella took over from me, so I was not involved in writing the paper about Hope, but my contribution is acknowledged.
I implemented the pattern matching code, and the idea of pattern compilation occurred to me. I remember showing it to Rod. He freaked out at first, but after about a five minute harangue, the penny dropped, and I remember him saying "clever Michael", "clever Michael" in his charming way.