refactor: Put return types as properties on implementations

src/core/PocomathInstance.mjs

@@ -2,7 +2,7 @@
 import typed from 'typed-function'
 import {makeChain} from './Chain.mjs'
 import {dependencyExtractor, generateTypeExtractor} from './extractors.mjs'
-import {R_, isReturnAnnotated} from './returns.mjs'
+import R_ from './returns.mjs'
 import {typeListOfSignature, typesOfSignature, subsetOfKeys} from './utils.mjs'
 
 const anySpec = {} // fixed dummy specification of 'any' type
@@ -693,7 +693,7 @@ export default class PocomathInstance {
          }
          /* Now build the catchall implementation */
          const self = this
-         /* For return-type annotation, we will have to fix this to
+         /* For return type annotation, we may have to fix this to
             propagate the return type. At the moment we are just bagging
          */
          const patch = (refs) => (...args) => {
@@ -815,12 +815,9 @@ export default class PocomathInstance {
                }
             }
             // Finally ready to make the call.
-            let returnSpec = behavior.does(innerRefs)
-            if (isReturnAnnotated(returnSpec)) {
-               // for now just drop return type information
-               returnSpec = returnSpec.via
-            }
-            return returnSpec(...args)
+            const implementation = behavior.does(innerRefs)
+            // Could do something with return type information here
+            return implementation(...args)
          }
          // The actual uses value needs to be a set:
          const outerUses = new Set(Object.values(simplifiedUses))
@@ -862,12 +859,9 @@ export default class PocomathInstance {
    _addTFimplementation(imps, signature, behavior) {
       const {uses, does} = behavior
       if (uses.length === 0) {
-         let returnSpec = does()
-         if (isReturnAnnotated(returnSpec)) {
-            // for now just dump the return information
-            returnSpec = returnSpec.via
-         }
-         imps[signature] = returnSpec
+         const implementation = does()
+         // could do something with return type information here
+         imps[signature] = implementation
          return
       }
       const refs = {}
@@ -927,13 +921,9 @@ export default class PocomathInstance {
       if (full_self_referential) {
          imps[signature] = this._typed.referToSelf(self => {
             refs.self = self
-            let returnSpec = does(refs)
-            if (isReturnAnnotated(returnSpec)) {
+            const implementation = does(refs)
             // What are we going to do with the return type info in here?
-               // Anyhow, drop it for now
-               returnSpec = returnSpec.via
-            }
-            return returnSpec
+            return implementation
          })
          return
       }
@@ -953,12 +943,9 @@ export default class PocomathInstance {
          }
          return
       }
-      let returnSpec = does(refs)
-      if (isReturnAnnotated(returnSpec)) {
-         // drop return type for now
-         returnSpec = returnSpec.via
-      }
-      imps[signature] = returnSpec
+      const implementation = does(refs)
+      // could do something with return type information here
+      imps[signature] = implementation
    }
 
    _correctPartialSelfRefs(name, imps) {
@@ -993,13 +980,9 @@ export default class PocomathInstance {
                for (let i = 0; i < part_self_references.length; ++i) {
                   refs[`self(${part_self_references[i]})`] = impls[i]
                }
-               let returnSpec = does(refs)
-               if (isReturnAnnotated(returnSpec)) {
+               const implementation = does(refs)
                // What will we do with the return type info in here?
-                  // anyhow, drop it for now
-                  returnSpec = returnSpec.via
-               }
-               return returnSpec
+               return implementation
             }
          )
       }

src/core/returns.mjs

@@ -1,10 +1,28 @@
 /* Annotate a function with its return type */
-export function R_(type, fn) {
-   return {returns: type, via: fn}
+
+/* Unfortunately JavaScript is missing a way to cleanly clone a function
+ * object, see https://stackoverflow.com/questions/1833588
+ */
+
+const clonedFrom = Symbol('the original function this one was cloned from')
+function cloneFunction(fn) {
+   const behavior = fn[clonedFrom] || fn // don't nest clones
+   const theClone = function () { return behavior.apply(this, arguments) }
+   Object.assign(theClone, fn)
+   theClone[clonedFrom] = body
+   Object.defineProperty(
+      theClone, 'name', {value: fn.name, configurable: true })
+   return theClone
 }
 
-export function isReturnAnnotated(x) {
-   return x && typeof x === 'object' && 'returns' in x && 'via' in x
+export function R_(type, fn) {
+   if ('returns' in fn) fn = cloneFunction(fn)
+   fn.returns = type
+   return fn
+}
+
+export function returnTypeOf(fn) {
+   return fn.returns || 'any'
 }
 
 export default R_