feat(PocomathInstance): Add .returnTypeOf method

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_ from './returns.mjs'
+import {R_, returnTypeOf} from './returns.mjs'
 import {typeListOfSignature, typesOfSignature, subsetOfKeys} from './utils.mjs'
 
 const anySpec = {} // fixed dummy specification of 'any' type
@@ -191,6 +191,16 @@ export default class PocomathInstance {
       return result
    }
 
+   /* Determine the return type of an operation given an input signature */
+   returnTypeOf(operation, signature) {
+      if (typeof operation === 'string') {
+         operation = this[operation]
+      }
+      if (!(this._typed.isTypedFunction(operation))) return 'any'
+      const details = this._typed.findSignature(operation, signature)
+      return returnTypeOf(details.fn)
+   }
+
    /* Return a chain object for this instance with a given value: */
    chain(value) {
       return makeChain(value, this, this._chainRepository)

test/_pocomath.mjs

@@ -20,6 +20,10 @@ describe('The default full pocomath instance "math"', () => {
       assert.strictEqual(math.typeOf({re: 6.28, im: 2.72}), 'Complex<number>')
    })
 
+   it('can determine the return types of operations', () => {
+      assert.strictEqual(math.returnTypeOf('negate', 'number'), 'number')
+   })
+
    it('can subtract numbers', () => {
       assert.strictEqual(math.subtract(12, 5), 7)
       //assert.strictEqual(math.subtract(3n, 1.5), 1.5)