feat(grid/traversers): add repeatWith traverser

It's very similar to branch() but has the option to omit the hexes from the source traverser. Also,
the name is a little better (hopefully)

src/grid/functions/index.ts

@@ -3,3 +3,4 @@ export * from './concat'
 export * from './distance'
 export * from './neighborOf'
 export * from './repeat'
+export * from './repeatWith'

src/grid/functions/repeatWith.ts

@@ -0,0 +1,25 @@
+import { Hex } from '../../hex'
+import { Traverser } from '../types'
+import { concat } from './concat'
+
+// todo: use in rays (if it still has right to exist)
+// todo: probably move repeatWith, repeat and concat to grid/traversers/
+export function repeatWith<T extends Hex>(
+  sources: Traverser<T> | Traverser<T>[],
+  targets: Traverser<T> | Traverser<T>[],
+  // todo: isn't there a more elegant way than a config?
+  { includeSource = true } = {},
+): Traverser<T, T[]> {
+  return function repeatWithTraverser(createHex, cursor) {
+    const hexes: T[] = []
+
+    for (const sourceCursor of concat(sources)(createHex, cursor)) {
+      if (includeSource) hexes.push(sourceCursor)
+      for (const hex of concat(targets)(createHex, sourceCursor)) {
+        hexes.push(hex)
+      }
+    }
+
+    return hexes
+  }
+}

src/grid/traversers/rays.ts

@@ -4,8 +4,9 @@ import { line } from './line'
 import { ring } from './ring'
 
 // todo:
+// - remove this file? If not: refactor to use repeatWith()?
 // - add option for arc in degrees?
-// - add to docs that duplicate hexes are returned (or make this configurable? Or add transformer that dedupes?)
+// - add to docs that duplicate hexes are returned (or make this configurable? Or add transducer that dedupes?)
 export function rays<T extends Hex>(options: RaysWithLengthOptions): Traverser<T, T[]>
 export function rays<T extends Hex>(options: RaysToHexOptions): Traverser<T, T[]>
 export function rays<T extends Hex>({

src/grid/traversers/rectangle.ts

@@ -1,7 +1,7 @@
 import { Compass, CompassDirection } from '../../compass'
 import { Hex, HexCoordinates, hexToOffset, OffsetCoordinates } from '../../hex'
 import { isOffset, isTuple, tupleToCube } from '../../utils'
-import { branch } from '../functions'
+import { repeatWith } from '../functions'
 import { Traverser } from '../types'
 import { line } from './line'
 
@@ -25,7 +25,7 @@ export function rectangle<T extends Hex>(
       ? optionsFromOpposingCorners(optionsOrCornerA as HexCoordinates, cornerB, createHex())
       : (optionsOrCornerA as RectangleOptions)
     const firstHex = createHex(start ?? cursor)
-    const hexes = branch<T>(
+    const hexes = repeatWith<T>(
       line({ start: firstHex, direction: Compass.rotate(direction, 2), length: height }),
       line({ direction, length: width - 1 }),
     )(createHex, firstHex)

src/grid/traversers/spiral.ts

@@ -1,14 +1,14 @@
 import { CompassDirection } from '../../compass'
 import { Hex, HexCoordinates } from '../../hex'
-import { branch } from '../functions'
+import { repeatWith } from '../functions'
 import { RotationLike, Traverser } from '../types'
 import { line } from './line'
 import { ring } from './ring'
 
 export function spiral<T extends Hex>({ radius, start, rotation }: SpiralOptions): Traverser<T, T[]> {
   return function spiralTraverser(createHex, cursor) {
     const center = createHex(start ?? cursor)
-    return branch<T>(line({ start, direction: CompassDirection.N, length: radius }), ring({ center, rotation }))(
+    return repeatWith<T>(line({ start, direction: CompassDirection.N, length: radius }), ring({ center, rotation }))(
       createHex,
       cursor,
     )