From fa63022656819b602d1013bc66897c7dd19b02d1 Mon Sep 17 00:00:00 2001
From: Glen Whitney <glen@studioinfinity.org>
Date: Thu, 22 Dec 2022 11:05:39 -0500
Subject: [PATCH] feat: add generic `square` operation and numeric `unequal`

---
 src/Complex/type.ts       | 13 +++++++++++++
 src/all.ts                |  1 +
 src/generic/all.ts        |  2 +-
 src/generic/arithmetic.ts | 26 ++++++++++++++++++++++++--
 4 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/Complex/type.ts b/src/Complex/type.ts
index a150700..36c040a 100644
--- a/src/Complex/type.ts
+++ b/src/Complex/type.ts
@@ -30,6 +30,19 @@ export interface ComplexReturn<Params> {
       : Params extends BBinary<infer B> ? Complex<B> // binary case
       : never
 
+   // alternatively if it seems better; each definition is simpler, but at
+   // the cost of having two keys here:
+   // complex_unary: Params extends [infer R] ? Complex<R> : never
+   // complex_binary: Params extends BBinary<infer R> ? Complex<R> : never
+
+   // There is actually a subtlety here that complex_unary really only works
+   // on real types that include their own zero value, so it should really be
+   // complex_unary: Params extends [infer R]
+   //    ? ImpReturns<'zero', [R]> extends R ? Complex<R> : never
+   //    : never
+   // and that might actually simplify some of the typings of other operations,
+   // but we'll leave such fine tuning til later, if we adopt this scheme
+
    zero: Params extends [infer Z] // unary
       ? Z extends Complex<infer T> // of a Complex parameter
          ? ImpReturns<'zero', T> extends T ? Z : never // that has its real 0
diff --git a/src/all.ts b/src/all.ts
index 192c7be..e2e83f1 100644
--- a/src/all.ts
+++ b/src/all.ts
@@ -1,2 +1,3 @@
 export * from './numbers/all.js'
 export * from './Complex/all.js'
+export * from './generic/all.js'
diff --git a/src/generic/all.ts b/src/generic/all.ts
index 40a35e4..1a008ac 100644
--- a/src/generic/all.ts
+++ b/src/generic/all.ts
@@ -6,5 +6,5 @@ export { generic }
 
 declare module "../core/Dispatcher" {
    interface ReturnTypes<Params>
-      extends ForType<'numbers', GenericReturn<Params>> { }
+      extends ForType<'generic', GenericReturn<Params>> { }
 }
diff --git a/src/generic/arithmetic.ts b/src/generic/arithmetic.ts
index 5cb4801..770c766 100644
--- a/src/generic/arithmetic.ts
+++ b/src/generic/arithmetic.ts
@@ -1,13 +1,35 @@
-import { ConservativeUnary, Dependency, ImpType, Signature } from "../core/Dispatcher";
+import { Dependency, ImpType, ImpReturns } from "../core/Dispatcher";
 
 declare module "./type" {
   interface GenericReturn<Params> {
     // Jos: not sure how to define this or why it is needed
-    square: Signature<Params, [T], T>
+    // square: Signature<Params, [T], T>
     // square: ConservativeUnary<Params, T>
     // square: Params extends [infer R]
     //   ? R extends number ? UnderlyingReal<R> : never
     //    : never
+
+    // The type of `square` in this interface, instantiated with the type
+    // Params of a parameter list, needs to be the return type of the
+    // operation `square` on those parameters. In other words, `square` gives
+    // a type transformer from the tuple type of its parameters to its return
+    // type.
+    // That's how Dispatcher knows what the return type will be in
+    // `Dependency<'square', [bigint]>`, for example: it instantiates
+    // GenericReturn with Params equal to [bigint] and then grabs the
+    // type of the `square` property. Hence we write:
+
+    square: Params extends [infer T] // square only takes 1 arbitrary parameter
+        ? ImpReturns<'multiply', [T, T]> // and returns whatever multiply does
+        : never; // otherwise if not a single argument, this implementation
+                 // doesn't handle it
+
+    // If square had more than one implementation in this collection, we could
+    // either add more conditional clauses to the above type transformer
+    // as I did in Complex/type.ts for `complex`, or we could have two
+    // different keys that both start with `square_` and Dispatcher will
+    // check both (as I have now done in comments in Complex/type.ts and
+    // verified that also works).
   }
 }