numbat/numbat/modules/core/lists.nbt

use core::scalar

fn len<A>(xs: List<A>) -> Scalar
fn head<A>(xs: List<A>) -> A
fn tail<A>(xs: List<A>) -> List<A>
fn cons<A>(x: A, xs: List<A>) -> List<A>

fn is_empty<A>(xs: List<A>) -> Bool = len(xs) == 0

# We definitely want to make the following functions generic, but this is not yet possible.

fn generate(n: Scalar, f: Fn[() -> Scalar]) -> List<Scalar> =
  if n == 0
    then []
    else cons(f(), generate(n - 1, f))

fn map(f: Fn[(Scalar) -> Scalar], xs: List<Scalar>) -> List<Scalar> =
  if len(xs) == 0
    then []
    else cons(f(head(xs)), map(f, tail(xs)))

fn cons_end(xs: List<Scalar>, x: Scalar) -> List<Scalar> =
  if is_empty(xs)
    then [x]
    else cons(head(xs), cons_end(tail(xs), x))

fn reverse(xs: List<Scalar>) -> List<Scalar> =
  if len(xs) == 0
    then []
    else cons_end(reverse(tail(xs)), head(xs))

fn sequence(n: Scalar) -> List<Scalar> =
  if n == 1
    then [0]
    else cons_end(sequence(n - 1), n - 1)

fn foldl(f: Fn[(Scalar, Scalar) -> Scalar], acc: Scalar, xs: List<Scalar>) -> Scalar =
  if len(xs) == 1
    then f(acc, head(xs))
    else foldl(f, f(acc, head(xs)), tail(xs))

fn const_5() -> Scalar = 5

fn inc(x: Scalar) -> Scalar = x + 1

fn add(x: Scalar, y: Scalar) -> Scalar = x + y
fn mul(x: Scalar, y: Scalar) -> Scalar = x * y