feat(stdlib): Add higher order array functions (#833)

* Add higher order array functions

* Fix new functions

* Replace for-each loops with regular for loops:

* Fix type errors

* Remove redundant clone

Author: jfecher

crates/nargo/tests/test_data/higher-order-functions/src/main.nr

@@ -1,3 +1,5 @@
+use dep::std;
+
 fn main() -> pub Field {
     let f = if 3 * 7 > 200 { foo } else { bar };
     constrain f()[1] == 2;
@@ -22,8 +24,26 @@ fn main() -> pub Field {
     x = x + 1;
     constrain (|y| y + z)(1) == 4;
     x = x + 1;
+    let ret = twice(add1, 3);
+
+    test_array_functions();
+
+    ret
+}
+
+/// Test the array functions in std::array
+fn test_array_functions() {
+    let myarray: [i32; 3] = [1, 2, 3];
+    constrain std::array::any(myarray, |n| n > 2);
+
+    let evens: [i32; 3] = [2, 4, 6];
+    constrain std::array::all(evens, |n| n > 1);
 
-    twice(add1, 3)
+    constrain std::array::fold(evens, 0, |a, b| a + b) == 12;
+    constrain std::array::reduce(evens, |a, b| a + b) == 12;
+    
+    let descending = std::array::sort_via(myarray, |a, b| a > b);
+    constrain descending == [3, 2, 1];
 }
 
 fn foo() -> [u32; 2] {

crates/noirc_frontend/src/hir/type_check/expr.rs

@@ -741,7 +741,7 @@ pub fn comparator_operand_type_rules(
 
             let comptime = CompTime::No(None);
             if other.try_bind_to_polymorphic_int(var, &comptime, true, op.location.span).is_ok() || other == &Type::Error {
-                Ok(other.clone())
+                Ok(Bool(comptime))
             } else {
                 Err(format!("Types in a binary operation should match, but found {lhs_type} and {rhs_type}"))
             }

noir_stdlib/src/array.nr

@@ -3,3 +3,56 @@ fn len<T>(_input : [T]) -> comptime Field {}
 
 #[builtin(arraysort)]
 fn sort<T, N>(_a: [T; N]) -> [T; N] {}
+
+// Sort with a custom sorting function.
+fn sort_via<T, N>(mut a: [T; N], ordering: fn(T, T) -> bool) -> [T; N] { 
+    for i in 1..len(a) {
+        for j in 0..i {
+            if ordering(a[i], a[j]) {
+                let old_a_j = a[j];
+                a[j] = a[i];
+                a[i] = old_a_j;
+            }
+        }
+    }
+    a
+}
+
+// Apply a function to each element of the array and an accumulator value,
+// returning the final accumulated value. This function is also sometimes
+// called `foldl`, `fold_left`, `reduce`, or `inject`.
+fn fold<T, U, N>(array: [T; N], mut accumulator: U, f: fn(U, T) -> U) -> U {
+    for i in 0 .. len(array) {
+        accumulator = f(accumulator, array[i]);
+    }
+    accumulator
+}
+
+// Apply a function to each element of the array and an accumulator value,
+// returning the final accumulated value. Unlike fold, reduce uses the first
+// element of the given array as its starting accumulator value.
+fn reduce<T, N>(array: [T; N], f: fn(T, T) -> T) -> T {
+    let mut accumulator = array[0];
+    for i in 1 .. len(array) {
+        accumulator = f(accumulator, array[i]);
+    }
+    accumulator
+}
+
+// Returns true if all elements in the array satisfy the predicate
+fn all<T, N>(array: [T; N], predicate: fn(T) -> bool) -> bool {
+    let mut ret = true;
+    for i in 0 .. len(array) {
+        ret &= predicate(array[i]);
+    }
+    ret
+}
+
+// Returns true if any element in the array satisfies the predicate
+fn any<T, N>(array: [T; N], predicate: fn(T) -> bool) -> bool {
+    let mut ret = false;
+    for i in 0 .. len(array) {
+        ret |= predicate(array[i]);
+    }
+    ret
+}