feat: Implement step one of the roadmap (#1)

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #1

src/steps/one.ts

@@ -0,0 +1,43 @@
+import { useTypes } from 'over.ts/src/index';
+
+const types = {
+   number: (x: unknown): x is number => typeof x === 'number',
+   bigint: (x: unknown): x is bigint => typeof x === 'bigint'
+}
+
+const overload = useTypes(types)
+
+const negate = overload({
+   'number -> number': (a: number): number => {
+      console.log('Negating number', a)
+      return -a
+   },
+   'bigint -> bigint': (a: bigint): bigint => {
+      console.log('Negating bigint', a)
+      return -a
+   }
+})
+
+console.log('Negation of 5 is', negate(5))
+console.log('Negation of 5n is', negate(5n))
+
+const add = overload({
+   'number, number -> number': (a: number, b: number): number => {
+      console.log('Adding numbers', a, b)
+      return a+b
+   },
+   'bigint, bigint -> bigint': (a: bigint, b: bigint): bigint => {
+      console.log('Adding bigints', a, b)
+      return a+b
+   }
+})
+
+console.log('Sum of 5 and 7 is', add(5,7))
+console.log('Sum of 5n and 7n is', add(5n, 7n))
+
+try {
+    //@ts-expect-error
+    console.log('Mixed sum is', add(5n, 7))
+} catch {
+    console.log('Mixed sum errored as expected.')
+}