1 files changed, 27 insertions, 0 deletions
diff --git a/src/prelude/array.ts b/src/prelude/array.ts
new file mode 100644
index 0000000000..54f7081712
--- /dev/null
+++ b/src/prelude/array.ts
@@ -0,0 +1,27 @@
+export function countIf<T>(f: (x: T) => boolean, xs: T[]): number {
+	return xs.filter(f).length;
+}
+
+export function count<T>(x: T, xs: T[]): number {
+	return countIf(y => x === y, xs);
+}
+
+export function concat<T>(xss: T[][]): T[] {
+	return ([] as T[]).concat(...xss);
+}
+
+export function intersperse<T>(sep: T, xs: T[]): T[] {
+	return concat(xs.map(x => [sep, x])).slice(1);
+}
+
+export function erase<T>(x: T, xs: T[]): T[] {
+	return xs.filter(y => x !== y);
+}
+
+export function unique<T>(xs: T[]): T[] {
+	return [...new Set(xs)];
+}
+
+export function sum(xs: number[]): number {
+	return xs.reduce((a, b) => a + b, 0);
+}