src/bigint/absquare.mjs

@@ -1,6 +1,7 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
 /* Absolute value squared */
 export const absquare = {
-    bigint: ({'square(bigint)': sqb}) => b => sqb(b)
+    bigint: ({'square(bigint)': sqb}) => Returns('bigint', b => sqb(b))
 }

src/bigint/add.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-export const add = {'bigint,bigint': () => (a,b) => a+b}
+export const add = {'bigint,bigint': () => Returns('bigint', (a,b) => a+b)}

src/bigint/compare.mjs

@@ -1,5 +1,7 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
 export const compare = {
-   'bigint,bigint': () => (a,b) => a === b ? 0n : (a > b ? 1n : -1n)
+   'bigint,bigint': () => Returns(
+      'boolean', (a,b) => a === b ? 0n : (a > b ? 1n : -1n))
 }

src/bigint/divide.mjs

@@ -1,12 +1,13 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
 export const divide = {
    'bigint,bigint': ({config, 'quotient(bigint,bigint)': quot}) => {
-      if (config.predictable) return quot
+      if (config.predictable) return Returns('bigint', (n,d) => quot(n,d))
-      return (n, d) => {
+      return Returns('bigint|undefined', (n, d) => {
          const q = n/d
          if (q * d == n) return q
          return undefined
-      }
+      })
    }
 }

src/bigint/isZero.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-export const isZero = {bigint: () => b => b === 0n}
+export const isZero = {bigint: () => Returns('boolean', b => b === 0n)}

src/bigint/multiply.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-export const multiply = {'bigint,bigint': () => (a,b) => a*b}
+export const multiply = {'bigint,bigint': () => Returns('bigint', (a,b) => a*b)}

src/bigint/native.mjs

@@ -1,12 +1,12 @@
 import gcdType from '../generic/gcdType.mjs'
-import {identity} from '../generic/identity.mjs'
+import {identityType} from '../generic/identity.mjs'
 
 export * from './Types/bigint.mjs'
 
 export {absquare} from './absquare.mjs'
 export {add} from './add.mjs'
 export {compare} from './compare.mjs'
-export const conjugate = {bigint: () => identity}
+export const conjugate = {bigint: identityType('bigint')}
 export {divide} from './divide.mjs'
 export const gcd = gcdType('bigint')
 export {isZero} from './isZero.mjs'

src/bigint/negate.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-export const negate = {bigint: () => b => -b}
+export const negate = {bigint: () => Returns('bigint', b => -b)}

src/bigint/one.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-export const one = {bigint: () => () => 1n}
+export const one = {bigint: () => Returns('bigint', () => 1n)}

src/bigint/quotient.mjs

@@ -1,13 +1,14 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-/* Returns the best integer approximation to n/d */
+/* Returns the floor integer approximation to n/d */
 export const quotient = {
-   'bigint,bigint': ({'sign(bigint)': sgn}) => (n, d) => {
+   'bigint,bigint': ({'sign(bigint)': sgn}) => Returns('bigint', (n, d) => {
       const dSgn = sgn(d)
       if (dSgn === 0n) return 0n
       if (sgn(n) === dSgn) return n/d
       const quot = n/d
       if (quot * d == n) return quot
       return quot - 1n
-   }
+   })
 }

src/bigint/roundquotient.mjs

@@ -1,8 +1,9 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
 /* Returns the closest integer approximation to n/d */
 export const roundquotient = {
-   'bigint,bigint': ({'sign(bigint)': sgn}) => (n, d) => {
+   'bigint,bigint': ({'sign(bigint)': sgn}) => Returns('bigint', (n, d) => {
       const dSgn = sgn(d)
       if (dSgn === 0n) return 0n
       const candidate = n/d
@@ -11,5 +12,5 @@ export const roundquotient = {
       if (2n * rem > absd) return candidate + dSgn
       if (-2n * rem >= absd) return candidate - dSgn
       return candidate
-   }
+   })
 }

src/bigint/sign.mjs

@@ -1,9 +1,10 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
 export const sign = {
-   bigint: () => b => {
+   bigint: () => Returns('bigint', b => {
       if (b === 0n) return 0n
       if (b > 0n) return 1n
       return -1n
-   }
+   })
 }

src/bigint/sqrt.mjs

@@ -1,5 +1,6 @@
-export * from './Types/bigint.mjs'
+import Returns from '../core/Returns.mjs'
 import isqrt from 'bigint-isqrt'
+export * from './Types/bigint.mjs'
 
 export const sqrt = {
    bigint: ({
@@ -11,18 +12,18 @@ export const sqrt = {
          // Don't just return the constant isqrt here because the object
          // gets decorated with info that might need to be different
          // for different PocomathInstancss
-         return b => isqrt(b)
+         return Returns('bigint', b => isqrt(b))
       }
       if (!cplx) {
-         return b => {
+         return Returns('bigint|undefined', b => {
             if (b >= 0n) {
                const trial = isqrt(b)
                if (trial * trial === b) return trial
             }
             return undefined
+         })
       }
-      }
+      return Returns('bigint|Complex<bigint>|undefined', b => {
-      return b => {
          if (b === undefined) return undefined
          let real = true
          if (b < 0n) {
@@ -33,6 +34,6 @@ export const sqrt = {
          if (trial * trial !== b) return undefined
          if (real) return trial
          return cplx(0n, trial)
-      }
+      })
    }
 }

src/bigint/zero.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/bigint.mjs'
 
-export const zero = {bigint: () => () => 0n}
+export const zero = {bigint: () => Returns('bigint', () => 0n)}

src/complex/Types/Complex.mjs

@@ -1,15 +1,14 @@
+import {Returns, returnTypeOf} from '../../core/Returns.mjs'
 import PocomathInstance from '../../core/PocomathInstance.mjs'
 
 const Complex = new PocomathInstance('Complex')
-// Base type that should generally not be used directly
+// Now the template type: Complex numbers are actually always homogeneous
-Complex.installType('Complex', {
+// in their component types. For an explanation of the meanings of the
-   test: z => z && typeof z === 'object' && 're' in z && 'im' in z
+// properties, see ../../tuple/Types/Tuple.mjs
-})
-// Now the template type: Complex numbers are actually always homeogeneous
-// in their component types.
 Complex.installType('Complex<T>', {
-   infer: ({typeOf, joinTypes}) => z => joinTypes([typeOf(z.re), typeOf(z.im)]),
+   base: z => z && typeof z === 'object' && 're' in z && 'im' in z,
    test: testT => z => testT(z.re) && testT(z.im),
+   infer: ({typeOf, joinTypes}) => z => joinTypes([typeOf(z.re), typeOf(z.im)]),
    from: {
       T: t => ({re: t, im: t-t}), // hack: maybe need a way to call zero(T)
       U: convert => u => {
@@ -21,7 +20,12 @@ Complex.installType('Complex<T>', {
 })
 
 Complex.promoteUnary = {
-   'Complex<T>': ({'self(T)': me, complex}) => z => complex(me(z.re), me(z.im))
+   'Complex<T>': ({
+      T,
+      'self(T)': me,
+      complex
+   }) => Returns(
+      `Complex<${returnTypeOf(me)}>`, z => complex(me(z.re), me(z.im)))
 }
 
 export {Complex}

src/complex/abs.mjs

@@ -1,10 +1,21 @@
+import {Returns, returnTypeOf} from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const abs = {
    'Complex<T>': ({
-      sqrt, // Calculation of the type needed in the square root (the
+      T,
-      // underlying numeric type of T, whatever T is, is beyond Pocomath's
+      sqrt, // Unfortunately no notation yet for the needed signature
-      // (current) template abilities, so punt and just do full resolution
+      'absquare(T)': baseabsq,
       'absquare(Complex<T>)': absq
-   }) => z => sqrt(absq(z))
+   }) => {
+      const midType = returnTypeOf(baseabsq)
+      const sqrtImp = sqrt.fromInstance.resolve('sqrt', midType, sqrt)
+      let retType = returnTypeOf(sqrtImp)
+      if (retType.includes('|')) {
+         // This is a bit of a hack, as it relies on all implementations of
+         // sqrt returning the "typical" return type as the first option
+         retType = retType.split('|',1)[0]
+      }
+      return Returns(retType, z => sqrtImp(absq(z)))
+   }
 }

src/complex/absquare.mjs

@@ -1,9 +1,27 @@
+import {Returns, returnTypeOf} from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const absquare = {
    'Complex<T>': ({
-      add, // Calculation of exact type needed in add (underlying numeric of T)
+      add, // no easy way to write the needed signature; if T is number
-      // is (currently) too involved for Pocomath
+           // it is number,number; but if T is Complex<bigint>, it is just
+           // bigint,bigint. So unfortunately we depend on all of add, and
+           // we extract the needed implementation below.
       'self(T)': absq
-   }) => z => add(absq(z.re), absq(z.im))
+   }) => {
+      const midType = returnTypeOf(absq)
+      const addImp = add.fromInstance.resolve(
+         'add', `${midType},${midType}`, add)
+      return Returns(
+         returnTypeOf(addImp), z => addImp(absq(z.re), absq(z.im)))
+   }
 }
+
+/* We could imagine notations that Pocomath could support that would simplify
+ * the above, maybe something like
+ * 'Complex<T>': ({
+ *    'self(T): U': absq,
+ *    'add(U,U):V': plus,
+ *    V
+ *  }) => Returns(V, z => plus(absq(z.re), absq(z.im)))
+ */

src/complex/add.mjs

@@ -1,8 +1,10 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const add = {
    'Complex<T>,Complex<T>': ({
+      T,
       'self(T,T)': me,
       'complex(T,T)': cplx
-   }) => (w,z) => cplx(me(w.re, z.re), me(w.im, z.im))
+   }) => Returns(`Complex<${T}>`, (w,z) => cplx(me(w.re, z.re), me(w.im, z.im)))
 }

src/complex/associate.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 /* Returns true if w is z multiplied by a complex unit */
@@ -9,9 +10,9 @@ export const associate = {
         'one(T)': uno,
         'complex(T,T)': cplx,
         'negate(Complex<T>)': neg
-    }) => (w,z) => {
+    }) => Returns('boolean', (w,z) => {
         if (eq(w,z) || eq(w,neg(z))) return true
         const ti = times(z, cplx(zr(z.re), uno(z.im)))
         return eq(w,ti) || eq(w,neg(ti))
-    }
+    })
 }

src/complex/complex.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 export * from '../generic/Types/generic.mjs'
 
@@ -6,15 +7,16 @@ export const complex = {
     * have a numeric/scalar type, e.g. by implementing subtypes in
     * typed-function
     */
-   'undefined': () => u => u,
+   'undefined': () => Returns('undefined', u => u),
-   'undefined,any': () => (u, y) => u,
+   'undefined,any': () => Returns('undefined', (u, y) => u),
-   'any,undefined': () => (x, u) => u,
+   'any,undefined': () => Returns('undefined', (x, u) => u),
-   'undefined,undefined': () => (u, v) => u,
+   'undefined,undefined': () => Returns('undefined', (u, v) => u),
-   'T,T': () => (x, y) => ({re: x, im: y}),
+   'T,T': ({T}) => Returns(`Complex<${T}>`, (x, y) => ({re: x, im: y})),
    /* Take advantage of conversions in typed-function */
    // 'Complex<T>': () => z => z
    /* But help out because without templates built in to typed-function,
     * type inference turns out to be too hard
     */
-   'T': ({'zero(T)': zr}) => x => ({re: x, im: zr(x)})
+   'T': ({T, 'zero(T)': zr}) => Returns(
+      `Complex<${T}>`, x => ({re: x, im: zr(x)}))
 }

src/complex/conjugate.mjs

@@ -1,9 +1,11 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const conjugate = {
    'Complex<T>': ({
+      T,
       'negate(T)': neg,
       'complex(T,T)': cplx
-   }) => z => cplx(z.re, neg(z.im))
+   }) => Returns(`Complex<${T}>`, z => cplx(z.re, neg(z.im)))
 }
 

src/complex/equalTT.mjs

@@ -1,9 +1,11 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const equalTT = {
    'Complex<T>,Complex<T>': ({
+      T,
       'self(T,T)': me
-   }) => (w,z) => me(w.re, z.re) && me(w.im, z.im),
+   }) => Returns('boolean', (w, z) => me(w.re, z.re) && me(w.im, z.im)),
    // NOTE: Although I do not understand exactly why, with typed-function@3.0's
    // matching algorithm, the above template must come first to ensure the
    // most specific match to a template call. I.e, if one of the below
@@ -11,16 +13,16 @@ export const equalTT = {
    // with (Complex<Complex<number>>, Complex<number>) (!, hopefully in some
    // future iteration typed-function will be smart enough to prefer
    // Complex<T>, Complex<T>. Possibly the problem is in Pocomath's bolted-on
-   // type resolution and the difficulty will go away when features are moved into
+   // type resolution and the difficulty will go away when features are moved
-   // typed-function.
+   // into typed-function.
    'Complex<T>,T': ({
       'isZero(T)': isZ,
       'self(T,T)': eqReal
-   }) => (z, x) => eqReal(z.re, x) && isZ(z.im),
+   }) => Returns('boolean', (z, x) => eqReal(z.re, x) && isZ(z.im)),
 
    'T,Complex<T>': ({
       'isZero(T)': isZ,
       'self(T,T)': eqReal
-   }) => (b, z) => eqReal(z.re, b) && isZ(z.im),
+   }) => Returns('boolean', (b, z) => eqReal(z.re, b) && isZ(z.im)),
 
 }

src/complex/gcd.mjs

@@ -1,4 +1,5 @@
 import PocomathInstance from '../core/PocomathInstance.mjs'
+import Returns from '../core/Returns.mjs'
 import * as  Complex from './Types/Complex.mjs'
 import gcdType from '../generic/gcdType.mjs'
 
@@ -9,15 +10,16 @@ const imps = {
    gcdComplexRaw,
    gcd: { // Only return gcds with positive real part
       'Complex<T>,Complex<T>': ({
+         T,
          'gcdComplexRaw(Complex<T>,Complex<T>)': gcdRaw,
          'sign(T)': sgn,
          'one(T)': uno,
          'negate(Complex<T>)': neg
-      }) => (z,m) => {
+      }) => Returns(`Complex<${T}>`, (z,m) => {
          const raw = gcdRaw(z, m)
          if (sgn(raw.re) === uno(raw.re)) return raw
          return neg(raw)
-      }
+      })
    }
 }
 

src/complex/invert.mjs

@@ -1,14 +1,16 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const invert = {
    'Complex<T>': ({
+      T,
       'conjugate(Complex<T>)': conj,
       'absquare(Complex<T>)': asq,
       'complex(T,T)': cplx,
       'divide(T,T)': div
-   }) => z => {
+   }) => Returns(`Complex<${T}>`, z => {
       const c = conj(z)
       const d = asq(z)
       return cplx(div(c.re, d), div(c.im, d))
-   }
+   })
 }

src/complex/isZero.mjs

@@ -1,5 +1,7 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const isZero = {
-   'Complex<T>': ({'self(T)': me}) => z => me(z.re) && me(z.im)
+   'Complex<T>': ({'self(T)': me}) => Returns(
+      'boolean', z => me(z.re) && me(z.im))
 }

src/complex/multiply.mjs

@@ -1,15 +1,20 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const multiply = {
    'Complex<T>,Complex<T>': ({
+      T,
       'complex(T,T)': cplx,
       'add(T,T)': plus,
-      'subtract(T,T)': sub,
+      'subtract(T,T)': subt,
       'self(T,T)': me,
       'conjugate(T)': conj // makes quaternion multiplication work
-   }) => (w,z) => {
+   }) => Returns(
-      return cplx(
+      `Complex<${T}>`,
-         sub(me(w.re, z.re), me(conj(w.im), z.im)),
+      (w,z) => {
-         plus(me(conj(w.re), z.im), me(w.im, z.re)))
+         const realpart = subt(me(     w.re,  z.re), me(conj(w.im), z.im))
+         const imagpart = plus(me(conj(w.re), z.im), me(     w.im,  z.re))
+         return cplx(realpart, imagpart)
       }
+   )
 }

src/complex/quaternion.mjs

@@ -1,5 +1,14 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
+// Might be nice to have type aliases!
 export const quaternion = {
-    'T,T,T,T': ({complex}) => (r,i,j,k) => complex(complex(r,j), complex(i,k))
+    'T,T,T,T': ({
+        T,
+        'complex(T,T)': cplxT,
+        'complex(Complex<T>,Complex<T>)': quat
+    }) => Returns(
+        `Complex<Complex<${T}>>`,
+        (r,i,j,k) => quat(cplxT(r,j), cplxT(i,k))
+    )
 }

src/complex/quotient.mjs

@@ -1,7 +1,9 @@
+import Returns from '../core/Returns.mjs'
 export * from './roundquotient.mjs'
 
 export const quotient = {
    'Complex<T>,Complex<T>': ({
+      T,
       'roundquotient(Complex<T>,Complex<T>)': rq
-   }) => (w,z) => rq(w,z)
+   }) => Returns(`Complex<${T}>`, (w,z) => rq(w,z))
 }

src/complex/roundquotient.mjs

@@ -1,17 +1,19 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const roundquotient = {
    'Complex<T>,Complex<T>': ({
+      T,
       'isZero(Complex<T>)': isZ,
       'conjugate(Complex<T>)': conj,
       'multiply(Complex<T>,Complex<T>)': mult,
       'absquare(Complex<T>)': asq,
       'self(T,T)': me,
       'complex(T,T)': cplx
-   }) => (n,d) => {
+   }) => Returns(`Complex<${T}>`, (n,d) => {
       if (isZ(d)) return d
       const cnum = mult(n, conj(d))
       const dreal = asq(d)
       return cplx(me(cnum.re, dreal), me(cnum.im, dreal))
-   }
+   })
 }

src/complex/sqrt.mjs

@@ -1,3 +1,4 @@
+import {Returns, returnTypeOf} from '../core/Returns.mjs'
 export * from './Types/Complex.mjs'
 
 export const sqrt = {
@@ -12,29 +13,41 @@ export const sqrt = {
       'multiply(T,T)': mult,
       'self(T)': me,
       'divide(T,T)': div,
-      'abs(Complex<T>)': absC,
+      'absquare(Complex<T>)': absqC,
       'subtract(T,T)': sub
    }) => {
+      let baseReturns = returnTypeOf(me)
+      if (baseReturns.includes('|')) {
+         // Bit of a hack, because it is relying on other implementations
+         // to list the "typical" value of sqrt first
+         baseReturns = baseReturns.split('|', 1)[0]
+      }
+
       if (config.predictable) {
-         return z => {
+         return Returns(`Complex<${baseReturns}>`, z => {
             const reOne = uno(z.re)
             if (isZ(z.im) && sgn(z.re) === reOne) return cplxU(me(z.re))
             const reTwo = plus(reOne, reOne)
+            const myabs = me(absqC(z))
             return cplxB(
-               mult(sgn(z.im), me(div(plus(absC(z),z.re), reTwo))),
+               mult(sgn(z.im), me(div(plus(myabs, z.re), reTwo))),
-               me(div(sub(absC(z),z.re), reTwo))
+               me(div(sub(myabs, z.re), reTwo))
             )
+         })
       }
-      }
+
-      return z => {
+      return Returns(
+         `Complex<${baseReturns}>|${baseReturns}|undefined`,
+         z => {
             const reOne = uno(z.re)
             if (isZ(z.im) && sgn(z.re) === reOne) return me(z.re)
             const reTwo = plus(reOne, reOne)
-         const reSqrt = me(div(plus(absC(z),z.re), reTwo))
+            const myabs = me(absqC(z))
-         const imSqrt = me(div(sub(absC(z),z.re), reTwo))
+            const reSqrt = me(div(plus(myabs, z.re), reTwo))
+            const imSqrt = me(div(sub(myabs, z.re), reTwo))
             if (reSqrt === undefined || imSqrt === undefined) return undefined
             return cplxB(mult(sgn(z.im), reSqrt), imSqrt)
          }
+      )
    }
 }
-

src/core/Returns.mjs

@@ -0,0 +1,34 @@
+/* Annotate a function with its return type */
+
+/* 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 Returns(type, fn) {
+   if ('returns' in fn) fn = cloneFunction(fn)
+   fn.returns = type
+   return fn
+}
+
+export function returnTypeOf(fn, signature, pmInstance) {
+   const typeOfReturns = typeof fn.returns
+   if (typeOfReturns === 'undefined') return 'any'
+   if (typeOfReturns === 'string') return fn.returns
+   // not sure if we will need a function to determine the return type,
+   // but allow it for now:
+   return fn.returns(signature, pmInstance)
+}
+
+export default Returns
+

src/core/utils.mjs

@@ -8,6 +8,8 @@ export function subsetOfKeys(set, obj) {
 
 /* Returns a list of the types mentioned in a typed-function signature */
 export function typeListOfSignature(signature) {
+   signature = signature.trim()
+   if (!signature) return []
    return signature.split(',').map(s => s.trim())
 }
 

src/generic/Types/adapted.mjs

@@ -1,4 +1,6 @@
 import PocomathInstance from '../../core/PocomathInstance.mjs'
+import Returns from '../../core/Returns.mjs'
+
 /* creates a PocomathInstance incorporating a new numeric type encapsulated
  * as a class. (This instance can the be `install()ed` in another to add the
  * type so created.)
@@ -22,15 +24,15 @@ export default function adapted(name, Thing, overrides) {
    // first a creator function, with name depending on the name of the thing:
    const creatorName = overrides.creatorName || name.toLowerCase()
    const creator = overrides[creatorName]
-      ? overrides[creatorName]('')
+      ? overrides[creatorName]['']
       : Thing[creatorName]
          ? (Thing[creatorName])
          : ((...args) => new Thing(...args))
    const defaultCreatorImps = {
-      '': () => () => creator(),
+      '': () => Returns(name, () => creator()),
-      '...any': () => args => creator(...args)
+      '...any': () => Returns(name, args => creator(...args))
    }
-   defaultCreatorImps[name] = () => x => x // x.clone(x)?
+   defaultCreatorImps[name] = () => Returns(name, x => x) // x.clone(x)?
    operations[creatorName] = overrides[creatorName] || defaultCreatorImps
 
    // We make the default instance, just as a place to check for methods
@@ -47,34 +49,35 @@ export default function adapted(name, Thing, overrides) {
       negate: 'neg'
    }
    const binaryOps = {
-      add: 'add',
+      add: ['add', name],
-      compare: 'compare',
+      compare: ['compare', name],
-      divide: 'div',
+      divide: ['div', name],
-      equalTT: 'equals',
+      equalTT: ['equals', 'boolean'],
-      gcd: 'gcd',
+      gcd: ['gcd', name],
-      lcm: 'lcm',
+      lcm: ['lcm', name],
-      mod: 'mod',
+      mod: ['mod', name],
-      multiply: 'mul',
+      multiply: ['mul', name],
-      subtract: 'sub'
+      subtract: ['sub', name]
    }
    for (const [mathname, standardname] of Object.entries(unaryOps)) {
       if (standardname in instance) {
          operations[mathname] = {}
-         operations[mathname][name] = () => t => t[standardname]()
+         operations[mathname][name] = () => Returns(name, t => t[standardname]())
       }
    }
    operations.zero = {}
-   operations.zero[name] = () => t => creator()
+   operations.zero[name] = () => Returns(name, t => creator())
    operations.one = {}
-   operations.one[name] = () => t => creator(1)
+   operations.one[name] = () => Returns(name, t => creator(1))
    operations.conjugate = {}
-   operations.conjugate[name] = () => t => t // or t.clone() ??
+   operations.conjugate[name] = () => Returns(name, t => t) // or t.clone() ??
 
    const binarySignature = `${name},${name}`
-   for (const [mathname, standardname] of Object.entries(binaryOps)) {
+   for (const [mathname, spec] of Object.entries(binaryOps)) {
-      if (standardname in instance) {
+      if (spec[0] in instance) {
          operations[mathname] = {}
-         operations[mathname][binarySignature] = () => (t,u) => t[standardname](u)
+         operations[mathname][binarySignature] = () => Returns(
+            spec[1], (t,u) => t[spec[0]](u))
       }
    }
    if ('operations' in overrides) {

src/generic/abs.mjs

@@ -1,7 +1,9 @@
+import Returns from '../core/Returns.mjs'
 export const abs = {
    T: ({
+      T,
       'smaller(T,T)': lt,
       'negate(T)': neg,
       'zero(T)': zr
-   }) => t => (smaller(t, zr(t)) ? neg(t) : t)
+   }) => Returns(T, t => (smaller(t, zr(t)) ? neg(t) : t))
 }

src/generic/absquare.mjs

@@ -1,6 +1,9 @@
+import Returns from '../core/Returns.mjs'
+
 export const absquare = {
    T: ({
+      T,
       'square(T)': sq,
       'abs(T)': abval
-   }) => t => sq(abval(t))
+   }) => Returns(T, t => sq(abval(t)))
 }

src/generic/all.mjs

@@ -1,5 +1,6 @@
 import {adapted} from './Types/adapted.mjs'
 import Fraction from 'fraction.js/bigfraction.js'
+import Returns from '../core/Returns.mjs'
 
 export * from './arithmetic.mjs'
 export * from './relational.mjs'
@@ -8,15 +9,18 @@ export const fraction = adapted('Fraction', Fraction, {
    before: ['Complex'],
    from: {number: n => new Fraction(n)},
    operations: {
-      compare: {'Fraction,Fraction': () => (f,g) => new Fraction(f.compare(g))},
+      compare: {
+         'Fraction,Fraction': () => Returns(
+            'Fraction', (f,g) => new Fraction(f.compare(g)))
+      },
       mod: {
-         'Fraction,Fraction': () => (n,d) => {
+         'Fraction,Fraction': () => Returns('Fraction', (n,d) => {
             // patch for "mathematician's modulus"
             // OK to use full public API of Fraction here
             const fmod = n.mod(d)
             if (fmod.s === -1n) return fmod.add(d.abs())
             return fmod
-         }
+         })
       }
    }
 })

src/generic/divide.mjs

@@ -1,7 +1,10 @@
+import Returns from '../core/Returns.mjs'
+
 export const divide = {
    'T,T': ({
+      T,
       'multiply(T,T)': multT,
       'invert(T)': invT
-   }) => (x, y) => multT(x, invT(y))
+   }) => Returns(T, (x, y) => multT(x, invT(y)))
 }
 

src/generic/gcdType.mjs

@@ -1,3 +1,5 @@
+import Returns from '../core/Returns.mjs'
+
 /* Note we do not use a template here so that we can explicitly control
  * which types this is instantiated for, namely the "integer" types, and
  * not simply allow Pocomath to generate instances for any type it encounters.
@@ -7,14 +9,14 @@ export default function(type) {
    const producer = refs => {
       const modder = refs[`mod(${type},${type})`]
       const zeroTester = refs[`isZero(${type})`]
-      return (a,b) => {
+      return Returns(type, (a,b) => {
          while (!zeroTester(b)) {
             const r = modder(a,b)
             a = b
             b = r
          }
          return a
-      }
+      })
    }
    const retval = {}
    retval[`${type},${type}`] = producer

src/generic/identity.mjs

@@ -1,3 +1,11 @@
-export function identity(x) {
+import Returns from '../core/Returns.mjs'
-   return x
+
+export function identityType(type) {
+   return () => Returns(type, x => x)
 }
+
+export function identitySubTypes(type) {
+   return ({T}) => Returns(T, x => x)
+}
+
+export const identity = {T: ({T}) => Returns(T, x => x)}

src/generic/lcm.mjs

@@ -1,10 +1,12 @@
+import Returns from '../core/Returns.mjs'
 import {reducingOperation} from './reducingOperation.mjs'
 
 export const lcm = {
    'T,T': ({
+      T,
       'multiply(T,T)': multT,
       'quotient(T,T)': quotT,
       'gcd(T,T)': gcdT
-   }) => (a,b) => multT(quotT(a, gcdT(a,b)), b)
+   }) => Returns(T, (a,b) => multT(quotT(a, gcdT(a,b)), b))
 }
 Object.assign(lcm, reducingOperation)

src/generic/mean.mjs

@@ -1,3 +1,8 @@
+import Returns from '../core/Returns.mjs'
 export const mean = {
-   '...any': ({add, divide}) => args => divide(add(...args), args.length)
+   '...T': ({
+      T,
+      add,
+      'divide(T,NumInt)': div
+   }) => Returns(T, args => div(add(...args), args.length))
 }

src/generic/mod.mjs

@@ -1,7 +1,10 @@
+import Returns from '../core/Returns.mjs'
+
 export const mod = {
    'T,T': ({
+      T,
       'subtract(T,T)': subT,
       'multiply(T,T)': multT,
       'quotient(T,T)': quotT
-   }) => (a,m) => subT(a, multT(m, quotT(a,m)))
+   }) => Returns(T, (a,m) => subT(a, multT(m, quotT(a,m))))
 }

src/generic/quotient.mjs

@@ -1,3 +1,9 @@
+import Returns from '../core/Returns.mjs'
+
 export const quotient = {
-    'T,T': ({'floor(T)': flr, 'divide(T,T)':div}) => (n,d) => flr(div(n,d))
+    'T,T': ({
+        T,
+        'floor(T)': flr,
+        'divide(T,T)': div
+    }) => Returns(T, (n,d) => flr(div(n,d)))
 }

src/generic/reducingOperation.mjs

@@ -1,13 +1,16 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/generic.mjs'
 
 export const reducingOperation = {
-   'undefined': () => u => u,
+   'undefined': () => Returns('undefined', u => u),
-   'undefined,...any': () => (u, rest) => u,
+   'undefined,...any': () => Returns('undefined', (u, rest) => u),
-   'any,undefined': () => (x, u) => u,
+   'any,undefined': () => Returns('undefined', (x, u) => u),
-   'undefined,undefined': () => (u,v) => u,
+   'undefined,undefined': () => Returns('undefined', (u,v) => u),
-   any: () => x => x,
+   T: ({T}) => Returns(T, x => x),
+   // Unfortunately the type language of Pocomath is not (yet?) expressive
+   // enough to properly type the full reduction signature here:
    'any,any,...any': ({
       self
-   }) => (a,b,rest) => [b, ...rest].reduce((x,y) => self(x,y), a)
+   }) => Returns('any', (a,b,rest) => [b, ...rest].reduce((x,y) => self(x,y), a))
 }
 

src/generic/relational.mjs

@@ -1,34 +1,45 @@
+import Returns from '../core/Returns.mjs'
+
 export const compare = {
-   'undefined,undefined': () => () => 0
+   'undefined,undefined': () => Returns('NumInt', () => 0)
 }
 
 export const isZero = {
-   'undefined': () => u => u === 0,
+   'undefined': () => Returns('boolean', u => u === 0),
-   T: ({'equal(T,T)': eq, 'zero(T)': zr}) => t => eq(t, zr(t))
+   T: ({
+      T,
+      'equal(T,T)': eq,
+      'zero(T)': zr
+   }) => Returns('boolean', t => eq(t, zr(t)))
 }
 
 export const equal = {
-   'any,any': ({equalTT, joinTypes, Templates, typeOf}) => (x,y) => {
+   'any,any': ({
+      equalTT,
+      joinTypes,
+      Templates,
+      typeOf
+   }) => Returns('boolean', (x,y) => {
       const resultant = joinTypes([typeOf(x), typeOf(y)], 'convert')
       if (resultant === 'any' || resultant in Templates) {
          return false
       }
       return equalTT(x,y)
-   }
+   })
 }
 
 export const equalTT = {
    'T,T': ({
       'compare(T,T)': cmp,
       'isZero(T)': isZ
-   }) => (x,y) => isZ(cmp(x,y)),
+   }) => Returns('boolean', (x,y) => isZ(cmp(x,y)))
    // If templates were native to typed-function, we should be able to
    // do something like:
    // 'any,any': () => () => false // should only be hit for different types
 }
 
 export const unequal = {
-   'any,any': ({equal}) => (x,y) => !(equal(x,y))
+   'any,any': ({equal}) => Returns('boolean', (x,y) => !(equal(x,y)))
 }
 
 export const larger = {
@@ -36,7 +47,7 @@ export const larger = {
       'compare(T,T)': cmp,
       'one(T)' : uno,
       'equalTT(T,T)' : eq
-   }) => (x,y) => eq(cmp(x,y), uno(y))
+   }) => Returns('boolean', (x,y) => eq(cmp(x,y), uno(y)))
 }
 
 export const largerEq = {
@@ -45,10 +56,10 @@ export const largerEq = {
       'one(T)' : uno,
       'isZero(T)' : isZ,
       'equalTT(T,T)': eq
-   }) => (x,y) => {
+   }) => Returns('boolean', (x,y) => {
       const c = cmp(x,y)
       return isZ(c) || eq(c, uno(y))
-   }
+   })
 }
 
 export const smaller = {
@@ -57,10 +68,10 @@ export const smaller = {
       'one(T)' : uno,
       'isZero(T)' : isZ,
       unequal
-   }) => (x,y) => {
+   }) => Returns('boolean', (x,y) => {
       const c = cmp(x,y)
       return !isZ(c) && unequal(c, uno(y))
-   }
+   })
 }
 
 export const smallerEq = {
@@ -68,5 +79,5 @@ export const smallerEq = {
       'compare(T,T)': cmp,
       'one(T)' : uno,
       unequal
-   }) => (x,y) => unequal(cmp(x,y), uno(y))
+   }) => Returns('boolean', (x,y) => unequal(cmp(x,y), uno(y)))
 }

src/generic/roundquotient.mjs

@@ -1,3 +1,9 @@
+import Returns from '../core/Returns.mjs'
+
 export const roundquotient = {
-    'T,T': ({'round(T)': rnd, 'divide(T,T)':div}) => (n,d) => rnd(div(n,d))
+   'T,T': ({
+      T,
+      'round(T)': rnd,
+      'divide(T,T)':div
+   }) => Returns(T, (n,d) => rnd(div(n,d)))
 }

src/generic/sign.mjs

@@ -1,3 +1,9 @@
+import Returns from '../core/Returns.mjs'
+
 export const sign = {
-   T: ({'compare(T,T)': cmp, 'zero(T)': Z}) => x => cmp(x, Z(x))
+   T: ({
+      T,
+      'compare(T,T)': cmp,
+      'zero(T)': Z
+   }) => Returns(T, x => cmp(x, Z(x)))
 }

src/generic/sqrt.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/generic.mjs'
 
-export const sqrt = {undefined: () => () => undefined}
+export const sqrt = {undefined: () => Returns('undefined', () => undefined)}

src/generic/square.mjs

@@ -1,3 +1,6 @@
+import {Returns, returnTypeOf} from '../core/Returns.mjs'
+
 export const square = {
-   T: ({'multiply(T,T)': multT}) => x => multT(x,x)
+   T: ({'multiply(T,T)': multT}) => Returns(
+      returnTypeOf(multT), x => multT(x,x))
 }

src/generic/subtract.mjs

@@ -1,3 +1,9 @@
+import Returns from '../core/Returns.mjs'
+
 export const subtract = {
-   'T,T': ({'add(T,T)': addT, 'negate(T)': negT}) => (x,y) => addT(x, negT(y))
+   'T,T': ({
+      T,
+      'add(T,T)': addT,
+      'negate(T)': negT
+   }) => Returns(T, (x,y) => addT(x, negT(y)))
 }

src/number/abs.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
-export const abs = {number: () => n => Math.abs(n)}
+export const abs = {'T:number': ({T}) => Returns(T, n => Math.abs(n))}

src/number/absquare.mjs

@@ -1,6 +1,7 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
 /* Absolute value squared */
 export const absquare = {
-    number: ({'square(number)': sqn}) => n => sqn(n)
+    'T:number': ({T, 'square(T)': sqn}) => Returns(T, n => sqn(n))
 }

src/number/add.mjs

@@ -1,3 +1,8 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
-export const add = {'number,number': () => (m,n) => m+n}
+export const add = {
+    // Note the below assumes that all subtypes of number that will be defined
+    // are closed under addition!
+    'T:number, T': ({T}) => Returns(T, (m,n) => m+n)
+}

src/number/compare.mjs

@@ -1,3 +1,5 @@
+import Returns from '../core/Returns.mjs'
+
 /* Lifted from mathjs/src/utils/number.js */
 /**
  * Minimum number added to one that makes the result different than one
@@ -48,5 +50,6 @@ function nearlyEqual (x, y, epsilon) {
 export const compare = {
   'number,number': ({
     config
-  }) => (x,y) => nearlyEqual(x, y, config.epsilon) ? 0 : (x > y ? 1 : -1)
+  }) => Returns(
+    'NumInt', (x,y) => nearlyEqual(x, y, config.epsilon) ? 0 : (x > y ? 1 : -1))
 }

src/number/invert.mjs

@@ -1,3 +1,5 @@
+import Returns from '../core/Returns.mjs'
+
 export * from './Types/number.mjs'
 
-export const invert = {number: () => n => 1/n}
+export const invert = {number: () => Returns('number', n => 1/n)}

src/number/isZero.mjs

@@ -1,6 +1,6 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
 export const isZero = {
-    number: () => n => n === 0,
+    'T:number': () => Returns('boolean', n => n === 0)
-    NumInt: () => n => n === 0  // necessary because of generic template
 }

src/number/multiply.mjs

@@ -1,3 +1,5 @@
+import Returns from '../core/Returns.mjs'
+
 export * from './Types/number.mjs'
 
-export const multiply = {'number,number': () => (m,n) => m*n}
+export const multiply = {'T:number,T': ({T}) => Returns(T, (m,n) => m*n)}

src/number/native.mjs

@@ -1,5 +1,5 @@
 import gcdType from '../generic/gcdType.mjs'
-import {identity} from '../generic/identity.mjs'
+import {identitySubTypes} from '../generic/identity.mjs'
 
 export * from './Types/number.mjs'
 
@@ -7,7 +7,7 @@ export {abs} from './abs.mjs'
 export {absquare} from './absquare.mjs'
 export {add} from './add.mjs'
 export {compare} from './compare.mjs'
-export const conjugate = {number: () => identity}
+export const conjugate = {'T:number': identitySubTypes('number')}
 export const gcd = gcdType('NumInt')
 export {invert} from './invert.mjs'
 export {isZero} from './isZero.mjs'

src/number/negate.mjs

@@ -1,3 +1,6 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
-export const negate = {number: () => n => -n}
+export const negate = {
+   'T:number': ({T}) => Returns(T, n => -n)
+}

src/number/one.mjs

@@ -1,3 +1,5 @@
+import Returns from '../core/Returns.mjs'
+
 export * from './Types/number.mjs'
 
-export const one = {number: () => () => 1}
+export const one = {number: () => Returns('NumInt', () => 1)}

src/number/quotient.mjs

@@ -1,15 +1,10 @@
+import Returns from '../core/Returns.mjs'
+
 export * from './Types/number.mjs'
 
-const intquotient = () => (n,d) => {
+export const quotient = {
+   'T:number,T': () => Returns('NumInt', (n,d) => {
       if (d === 0) return d
       return Math.floor(n/d)
-}
+   })
-
-export const quotient = {
-   // Hmmm, seem to need all of these because of the generic template version
-   // Should be a way around that
-   'NumInt,NumInt': intquotient,
-   'NumInt,number': intquotient,
-   'number,NumInt': intquotient,
-   'number,number': intquotient
 }

src/number/roundquotient.mjs

@@ -1,8 +1,10 @@
+import Returns from '../core/Returns.mjs'
+
 export * from './Types/number.mjs'
 
 export const roundquotient = {
-   'number,number': () => (n,d) => {
+   'number,number': () => Returns('NumInt', (n,d) => {
       if (d === 0) return d
       return Math.round(n/d)
-   }
+   })
 }

src/number/sqrt.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
 export const sqrt = {
@@ -6,12 +7,12 @@ export const sqrt = {
       'complex(number,number)': cplx,
       'negate(number)': neg}) => {
          if (config.predictable || !cplx) {
-         return n => isNaN(n) ? NaN : Math.sqrt(n)
+            return Returns('number', n => isNaN(n) ? NaN : Math.sqrt(n))
          }
-      return n => {
+         return Returns('number|Complex<number>', n => {
             if (isNaN(n)) return NaN
             if (n >= 0) return Math.sqrt(n)
             return cplx(0, Math.sqrt(neg(n)))
-      }
+         })
       }
 }

src/number/zero.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export * from './Types/number.mjs'
 
-export const zero = {number: () => () => 0}
+export const zero = {number: () => Returns('NumInt', () => 0)}

src/ops/choose.mjs

@@ -1,11 +1,13 @@
-/* Note this is not a good algorithm for computing binomial coefficients,
+import Returns from '../core/Returns.mjs'
+
+/* Note this is _not_ a good algorithm for computing binomial coefficients,
  * it's just for demonstration purposes
  */
 export const choose = {
-   'NumInt,NumInt': ({factorial}) => (n,k) => Number(
+   'NumInt,NumInt': ({factorial}) => Returns(
-      factorial(n) / (factorial(k)*factorial(n-k))),
+      'NumInt', (n,k) => Number(factorial(n) / (factorial(k)*factorial(n-k)))),
    'bigint,bigint': ({
       factorial
-   }) => (n,k) => factorial(n) / (factorial(k)*factorial(n-k))
+   }) => Returns('bigint', (n,k) => factorial(n) / (factorial(k)*factorial(n-k)))
 }
         

src/ops/factorial.mjs

@@ -1,8 +1,15 @@
-export function factorial(n) {
+import Returns from '../core/Returns.mjs'
+
+/* Plain functions are OK, too, and they can be decorated with a return type
+ * just like an implementation.
+ */
+const factorial = Returns('bigint', function factorial(n) {
    n = BigInt(n)
    let prod = 1n
    for (let i = n; i > 1n; --i) {
       prod *= i
    }
    return prod
-}
+})
+
+export {factorial}

src/ops/floor.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 import {Complex} from '../complex/Types/Complex.mjs'
 
 /* Note we don't **export** any types here, so that only the options
@@ -5,26 +6,28 @@ import {Complex} from '../complex/Types/Complex.mjs'
  */
 
 export const floor = {
-   bigint: () => x => x,
+   /* Because Pocomath isn't part of typed-function, nor does it have access
-   NumInt: () => x => x, // Because Pocomath isn't part of typed-function, or
+    * to the real typed-function parse, we unfortunately can't coalesce the
-   'Complex<bigint>': () => x => x, // at least have access to the real
+    * first several implementations into one entry with type
-   // typed-function parse, we unfortunately can't coalesce these into one
+    * `bigint|NumInt|GaussianInteger` because then they couldn't
-   // entry with type `bigint|NumInt|GaussianInteger` because they couldn't
+    * be separately activated
-   // be separately activated then
+    */
+   bigint: () => Returns('bigint', x => x),
+   NumInt: () => Returns('NumInt', x => x),
+   'Complex<bigint>': () => Returns('Complex<bigint>', x => x),
 
-   number: ({'equalTT(number,number)': eq}) => n => {
+   number: ({'equalTT(number,number)': eq}) => Returns('NumInt', n => {
       if (eq(n, Math.round(n))) return Math.round(n)
       return Math.floor(n)
-   },
+   }),
 
    'Complex<T>': Complex.promoteUnary['Complex<T>'],
 
    // OK to include a type totally not in Pocomath yet, it'll never be
    // activated.
-   // Fraction: ({quotient}) => f => quotient(f.n, f.d), // oops have that now
    BigNumber: ({
       'round(BigNumber)': rnd,
       'equal(BigNumber,BigNumber)': eq
-   }) => x => eq(x,round(x)) ? round(x) : x.floor()
+   }) => Returns('BigNumber', x => eq(x,round(x)) ? round(x) : x.floor())
 
 }

src/tuple/Types/Tuple.mjs

@@ -1,25 +1,24 @@
 /* A template type representing a homeogeneous tuple of elements */
 import PocomathInstance from '../../core/PocomathInstance.mjs'
+import {Returns, returnTypeOf} from '../../core/Returns.mjs'
 
 const Tuple = new PocomathInstance('Tuple')
-// First a base type that will generally not be used directly
+
-Tuple.installType('Tuple', {
-   test: t => t && typeof t === 'object' && 'elts' in t && Array.isArray(t.elts)
-})
-// Now the template type that is the primary use of this
 Tuple.installType('Tuple<T>', {
-   // We are assuming that any 'Type<T>' refines 'Type', so this is
+   // A test that "defines" the "base type", which is not really a type
-   // not necessary:
+   // (only fully instantiated types are added to the universe)
-   // refines: 'Tuple',
+   base: t => t && typeof t === 'object' && 'elts' in t && Array.isArray(t.elts),
-   // But we need there to be a way to determine the type of a tuple:
+   // The template portion of the test; it takes the test for T as
-   infer: ({typeOf, joinTypes}) => t => joinTypes(t.elts.map(typeOf)),
+   // input and returns the test for an entity _that already passes
-   // For the test, we can assume that t is already a base tuple,
+   // the base test_ to be a Tuple<T>:
-   // and we get the test for T as an input and we have to return
-   // the test for Tuple<T>
    test: testT => t => t.elts.every(testT),
-   // These are only invoked for types U such that there is already
+   // And we need there to be a way to determine the (instantiation)
-   // a conversion from U to T, and that conversion is passed as an input
+   // type of an tuple (that has already passed the base test):
-   // and we have to return the conversion to Tuple<T>:
+   infer: ({typeOf, joinTypes}) => t => joinTypes(t.elts.map(typeOf)),
+   // Conversions. Parametrized conversions are only invoked for types
+   // U such that there is already a conversion from U to T, and that
+   // conversion is passed as an input, and we have to return the conversion
+   // function from the indicated template in terms of U to Tuple<T>:
    from: {
       'Tuple<U>': convert => tu => ({elts: tu.elts.map(convert)}),
       // Here since there is no U it's a straight conversion:
@@ -35,13 +34,20 @@ Tuple.promoteUnary = {
    'Tuple<T>': ({
       'self(T)': me,
       tuple
-   }) => t => tuple(...(t.elts.map(x => me(x)))) // NOTE: this must use
+   }) => {
-   // the inner arrow function to drop additional arguments that Array.map
+      const compType = me.fromInstance.joinTypes(
-   // supplies, as otherwise the wrong signature of `me` might be used.
+         returnTypeOf(me).split('|'), 'convert')
+      return Returns(
+         `Tuple<${compType}>`, t => tuple(...(t.elts.map(x => me(x)))))
+   }
 }
 
 Tuple.promoteBinaryUnary = {
-   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, 'self(T)': meU, tuple}) => (s,t) => {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, 'self(T)': meU, tuple}) => {
+      const compTypes = returnTypeOf(meB).split('|').concat(
+         returnTypeOf(meU).split('|'))
+      const compType = meU.fromInstance.joinTypes(compTypes, 'convert')
+      return Returns(`Tuple<${compType}>`, (s,t) => {
          let i = -1
          let result = []
          while (true) {
@@ -55,22 +61,30 @@ Tuple.promoteBinaryUnary = {
             else break
          }
          return tuple(...result)
+      })
    }
 }
 
 Tuple.promoteBinary = {
-   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, tuple}) => (s,t) => {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, tuple}) => {
+      const compType = meB.fromInstance.joinTypes(
+         returnTypeOf(meB).split('|'))
+      return Returns(`Tuple<${compType}>`, (s,t) => {
          const lim = Math.max(s.elts.length, t.elts.length)
          const result = []
          for (let i = 0; i < lim; ++i) {
             result.push(meB(s.elts[i], t.elts[i]))
          }
          return tuple(...result)
+      })
    }
 }
 
 Tuple.promoteBinaryStrict = {
-   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, tuple}) => (s,t) => {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, tuple}) => {
+      const compType = meB.fromInstance.joinTypes(
+         returnTypeOf(meB).split('|'))
+      return Returns(`Tuple<${compType}>`, (s,t) => {
          if (s.elts.length !== t.elts.length) {
             throw new RangeError('Tuple length mismatch') // get name of self ??
          }
@@ -79,6 +93,7 @@ Tuple.promoteBinaryStrict = {
             result.push(meB(s.elts[i], t.elts[i]))
          }
          return tuple(...result)
+      })
    }
 }
 

src/tuple/equalTT.mjs

@@ -1,11 +1,16 @@
+import Returns from '../core/Returns.mjs'
+
 export * from './Types/Tuple.mjs'
 
 export const equalTT = {
-   'Tuple<T>,Tuple<T>': ({'self(T,T)': me, 'length(Tuple)': len}) => (s,t) => {
+   'Tuple<T>,Tuple<T>': ({
+      'self(T,T)': me,
+      'length(Tuple)': len
+   }) => Returns('boolean', (s,t) => {
       if (len(s) !== len(t)) return false
       for (let i = 0; i < len(s); ++i) {
          if (!me(s.elts[i], t.elts[i])) return false
       }
       return true
-   }
+   })
 }

src/tuple/isZero.mjs

@@ -1,7 +1,10 @@
+import Returns from '../core/Returns.mjs'
+
 export {Tuple} from './Types/Tuple.mjs'
 
 export const isZero = {
-   'Tuple<T>': ({'self(T)': me}) => t => t.elts.every(e => me(e))
+   'Tuple<T>': ({'self(T)': me}) => Returns(
+      'boolean', t => t.elts.every(e => me(e)))
    // Note we can't just say `every(me)` above since every invokes its
    // callback with more arguments, which then violates typed-function's
    // signature for `me`

src/tuple/length.mjs

@@ -1,3 +1,4 @@
+import Returns from '../core/Returns.mjs'
 export {Tuple} from './Types/Tuple.mjs'
 
-export const length = {Tuple: () => t => t.elts.length}
+export const length = {'Tuple<T>': () => Returns('NumInt', t => t.elts.length)}

src/tuple/tuple.mjs

@@ -1,6 +1,10 @@
+import Returns from '../core/Returns.mjs'
+
 export {Tuple} from './Types/Tuple.mjs'
 
 /* The purpose of the template argument is to ensure that all of the args
  * are convertible to the same type.
  */
-export const tuple = {'...T': () => args => ({elts: args})}
+export const tuple = {
+    '...T': ({T}) => Returns(`Tuple<${T}>`, args => ({elts: args}))
+}

test/_pocomath.mjs

@@ -20,9 +20,56 @@ 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')
+      assert.strictEqual(math.returnTypeOf('negate', 'NumInt'), 'NumInt')
+      math.negate(math.complex(1.2, 2.8)) // TODO: make this call unnecessary
+      assert.strictEqual(
+         math.returnTypeOf('negate', 'Complex<number>'), 'Complex<number>')
+      assert.strictEqual(math.returnTypeOf('add', 'number,number'), 'number')
+      assert.strictEqual(math.returnTypeOf('add', 'NumInt,NumInt'), 'NumInt')
+      assert.strictEqual(math.returnTypeOf('add', 'NumInt,number'), 'number')
+      assert.strictEqual(math.returnTypeOf('add', 'number,NumInt'), 'number')
+      assert.deepStrictEqual(  // TODO: ditto
+         math.add(3, math.complex(2.5, 1)), math.complex(5.5, 1))
+      assert.strictEqual(
+         math.returnTypeOf('add', 'Complex<number>,NumInt'), 'Complex<number>')
+      // The following is not actually what we want, but the Pocomath type
+      // language isn't powerful enough at this point to capture the true
+      // return type:
+      assert.strictEqual(
+         math.returnTypeOf('add', 'number,NumInt,Complex<number>'), 'any')
+      assert.strictEqual(
+         math.returnTypeOf('chain', 'bigint'), 'Chain<bigint>')
+      assert.strictEqual(
+         math.returnTypeOf('returnTypeOf', 'string,string'), 'string')
+      assert.strictEqual(
+         math.returnTypeOf('conjugate', 'bigint'), 'bigint')
+      assert.strictEqual(
+         math.returnTypeOf('gcd', 'bigint,bigint'), 'bigint')
+      math.identity(math.fraction(3,5)) // TODO: ditto
+      assert.strictEqual(math.returnTypeOf('identity', 'Fraction'), 'Fraction')
+      assert.strictEqual(
+         math.returnTypeOf('quotient', 'bigint,bigint'), 'bigint')
+      math.abs(math.complex(2,1)) //TODO: ditto
+      assert.strictEqual(
+         math.returnTypeOf('abs','Complex<NumInt>'), 'number')
+      math.multiply(math.quaternion(1,1,1,1), math.quaternion(1,-1,1,-1)) // dit
+      const quatType = math.returnTypeOf(
+         'quaternion', 'NumInt,NumInt,NumInt,NumInt')
+      assert.strictEqual(quatType, 'Complex<Complex<NumInt>>')
+      assert.strictEqual(
+         math.returnTypeOf('multiply', quatType + ',' + quatType), quatType)
+      assert.strictEqual(math.returnTypeOf('isZero', 'NumInt'), 'boolean')
+      assert.strictEqual(
+         math.returnTypeOf('roundquotient', 'NumInt,number'), 'NumInt')
+      assert.strictEqual(
+         math.returnTypeOf('factorial', 'NumInt'), 'bigint')
+   })
+
    it('can subtract numbers', () => {
       assert.strictEqual(math.subtract(12, 5), 7)
-      //assert.strictEqual(math.subtract(3n, 1.5), 1.5)
+      assert.throws(() => math.subtract(3n, 1.5), 'TypeError')
    })
 
    it('can add numbers', () => {

test/complex/_all.mjs

@@ -39,8 +39,8 @@ describe('complex', () => {
    })
 
    it('checks for equality', () => {
-      assert.ok(math.equal(math.complex(3,0), 3))
+      assert.ok(math.equal(math.complex(3, 0), 3))
-      assert.ok(math.equal(math.complex(3,2), math.complex(3, 2)))
+      assert.ok(math.equal(math.complex(3, 2), math.complex(3, 2)))
       assert.ok(!(math.equal(math.complex(45n, 3n), math.complex(45n, -3n))))
       assert.ok(!(math.equal(math.complex(45n, 3n), 45n)))
    })
@@ -83,6 +83,7 @@ describe('complex', () => {
       assert.deepStrictEqual(
          math.multiply(q0, math.quaternion(2, 1, 0.1, 0.1)),
          math.quaternion(1.9, 1.1, 2.1, -0.9))
+      math.absquare(math.complex(1.25, 2.5)) //HACK: need absquare(Complex<number>)
       assert.strictEqual(math.abs(q0), Math.sqrt(2))
       assert.strictEqual(math.abs(q1), Math.sqrt(33)/4)
    })

test/core/_utils.mjs

@@ -0,0 +1,8 @@
+import assert from 'assert'
+import * as utils from '../../src/core/utils.mjs'
+
+describe('typeListOfSignature', () => {
+   it('returns an empty list for the empty signature', () => {
+      assert.deepStrictEqual(utils.typeListOfSignature(''), [])
+   })
+})

test/custom.mjs

@@ -135,13 +135,8 @@ describe('A custom instance', () => {
       assert.strictEqual(
          inst.typeMerge(3, inst.complex(4.5,2.1)),
          'Merge to Complex<number>')
-      // The following is the current behavior, since 3 converts to 3+0i
+      assert.throws(
-      // which is technically the same Complex type as 3n+0ni.
+         () => inst.typeMerge(3, inst.complex(3n)), TypeError)
-      // This should clear up when Complex is templatized
-      assert.strictEqual(inst.typeMerge(3, inst.complex(3n)), 'Merge to Complex')
-      // But types that truly cannot be merged should throw a TypeError
-      // Should add a variation of this with a more usual type once there is
-      // one not interconvertible with others...
       inst.install(genericSubtract)
       assert.throws(() => inst.typeMerge(3, undefined), TypeError)
    })

test/generic/_all.mjs

@@ -0,0 +1,20 @@
+import assert from 'assert'
+import math from '../../src/pocomath.mjs'
+
+describe('generic', () => {
+   it('calculates mean', () => {
+      assert.strictEqual(math.mean(1,2.5,3.25,4.75), 2.875)
+      assert.strictEqual(
+         math.returnTypeOf('mean', 'number,number,number,number'),
+         'number'
+      )
+   })
+   it('compares things', () => {
+      assert.strictEqual(math.larger(7n, 3n), true)
+      assert.strictEqual(
+         math.returnTypeOf('larger', 'bigint,bigint'), 'boolean')
+      assert.strictEqual(math.smallerEq(7.2, 3), false)
+      assert.strictEqual(
+         math.returnTypeOf('smallerEq', 'number,NumInt'), 'boolean')
+   })
+})

test/generic/fraction.mjs

@@ -92,4 +92,10 @@ describe('fraction', () => {
       assert.deepStrictEqual(math.square(tf), math.fraction(9/16))
    })
 
+   it('knows the types of its operations', () => {
+      assert.deepStrictEqual(
+         math.returnTypeOf('ceiling', 'Fraction'), 'Fraction')
+      assert.deepStrictEqual(
+         math.returnTypeOf('multiply', 'Fraction,Fraction'), 'Fraction')
+   })
 })

test/tuple/_native.mjs

@@ -8,14 +8,12 @@ describe('tuple', () => {
 
    it('does not allow unification by converting consecutive arguments', () => {
       assert.throws(() => math.tuple(3, 5.2, 2n), /TypeError.*unif/)
-      // Hence, the order matters in a slightly unfortunate way,
-      // but I think being a little ragged in these edge cases is OK:
       assert.throws(
          () => math.tuple(3, 2n, math.complex(5.2)),
          /TypeError.*unif/)
-      assert.deepStrictEqual(
+      assert.throws(
-         math.tuple(3, math.complex(2n), 5.2),
+         () => math.tuple(3, math.complex(2n), 5.2),
-         {elts: [math.complex(3), math.complex(2n), math.complex(5.2)]})
+         /TypeError.*unif/)
    })
 
    it('can be tested for zero and equality', () => {
@@ -56,6 +54,9 @@ describe('tuple', () => {
       assert.deepStrictEqual(
          math.subtract(math.tuple(3n,4n,5n), math.tuple(2n,1n,0n)),
          math.tuple(1n,3n,5n))
+      assert.deepStrictEqual(
+         math.returnTypeOf('subtract', 'Tuple<bigint>,Tuple<bigint>'),
+         'Tuple<bigint>')
       assert.throws(
          () => math.subtract(math.tuple(5,6), math.tuple(7)),
          /RangeError/)
@@ -106,9 +107,16 @@ describe('tuple', () => {
    })
 
    it('supports sqrt', () => {
+      const mixedTuple = math.tuple(2, math.complex(0,2), 1.5)
       assert.deepStrictEqual(
-         math.sqrt(math.tuple(4,-4,2.25)),
+         mixedTuple,
-         math.tuple(2, math.complex(0,2), 1.5))
+         math.tuple(math.complex(2), math.complex(0,2), math.complex(1.5)))
+      assert.strictEqual(
+         math.returnTypeOf('tuple', 'NumInt, Complex<NumInt>, number'),
+         'Tuple<Complex<number>>')
+      assert.deepStrictEqual(math.sqrt(math.tuple(4,-4,2.25)), mixedTuple)
+      assert.strictEqual(
+         math.returnTypeOf('sqrt', 'Tuple<NumInt>'), 'Tuple<Complex<number>>')
    })
 
 })