Declare implementations and dependencies via standard interfaces for operations (#8)

Adds a new subdirectory `interfaces` where standard interfaces
  are defined. Additional interfaces for a given operation can
  be added with an `AliasOf` type operator. Provides type
  operators that give the return type, full function type, and
  the type of a dependency on, a given operator.

  Resolves #6.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Co-authored-by: Jos de Jong <wjosdejong@gmail.com>
Reviewed-on: #8

src/numbers/type.ts

@@ -1,7 +1,25 @@
+import type { Signature } from '../interfaces/type.js'
+
 export const number_type = {
    before: ['Complex'],
    test: (n: unknown): n is number => typeof n === 'number',
-   from: {string: s => +s}
+   from: { string: (s: string) => +s }
 }
 
-export const zero = (a: number) => 0
+declare module "../interfaces/type" {
+   interface AssociatedTypes<T> {
+      numbers: {
+         type: number
+         zero: 0
+         one: 1
+         nan: typeof NaN
+         real: number
+      }
+   }
+}
+
+// I don't like the redundancy of repeating 'zero'; any way to eliminate that?
+export const zero: Signature<'zero', number> = (a) => 0
+export const one:  Signature<'one',  number> = (a) => 1
+export const nan:  Signature<'nan',  number> = (a) => NaN
+export const re:   Signature<'re',   number> = (a) => a