Pattern Matching in Other Languages¶

If you already know Rust, Scala, Haskell, or OCaml, Patternia should feel familiar at the semantic level:

Expression-Oriented Matching¶

Rust:

let label = match x {
    0 => "zero",
    1 => "one",
    _ => "many",
};

Patternia:

auto label = match(x) | on(
  lit(0) >> "zero",
  lit(1) >> "one",
  _ >> "many"
);

Many languages bind inside the pattern syntax. Patternia keeps binding explicit because it is a C++ library:

match(value) | on(
  $ >> [](auto v) { process(v); },
  _ >> [] {}
);

Patternia guards refine a bound case:

auto label = match(x) | on(
  $[PTN_LET(value, value > 0 && value < 10)] >> "small",
  _ >> "other"
);

Without native language destructuring, Patternia uses explicit member pointers:

auto label = match(user) | on(
  $(has<&User::age, &User::active>)[arg<0> < 18 && arg<1> == true]
      >> "minor",
  _ >> "adult"
);

Patternia does not try to copy another language's syntax. It translates the same ideas into a small C++ DSL: