Add product proc (#7951)

* Add product proc

* Update changelog

changelog.md

@@ -65,6 +65,7 @@
 - Added cotangent, secant and cosecant procs ``math.cot``, ``math.sec`` and ``math.csc``; and their hyperbolic, inverse and inverse hyperbolic functions, ``math.coth``, ``math.sech``, ``math.csch``, ``math.arccot``, ``math.arcsec``, ``math.arccsc``, ``math.arccoth``, ``math.arcsech`` and ``math.arccsch`` procs.
 - Added the procs ``math.floorMod`` and ``math.floorDiv`` for floor based integer division.
 - Added the procs ``rationals.`div```, ``rationals.`mod```, ``rationals.floorDiv`` and ``rationals.floorMod`` for rationals.
+- Added the proc ``math.prod`` for product of elements in openArray.
 
 ### Library changes
 

lib/pure/math.nim

@@ -129,6 +129,12 @@ proc sum*[T](x: openArray[T]): T {.noSideEffect.} =
   ## If `x` is empty, 0 is returned.
   for i in items(x): result = result + i
 
+proc prod*[T](x: openArray[T]): T {.noSideEffect.} =
+  ## Computes the product of the elements in ``x``.
+  ## If ``x`` is empty, 1 is returned.
+  result = 1.T
+  for i in items(x): result = result * i
+
 {.push noSideEffect.}
 when not defined(JS): # C
   proc sqrt*(x: float32): float32 {.importc: "sqrtf", header: "<math.h>".}
@@ -560,6 +566,12 @@ when isMainModule:
   # Function for approximate comparison of floats
   proc `==~`(x, y: float): bool = (abs(x-y) < 1e-9)
 
+  block: # prod
+    doAssert prod([1, 2, 3, 4]) == 24
+    doAssert prod([1.5, 3.4]) == 5.1
+    let x: seq[float] = @[]
+    doAssert prod(x) == 1.0
+
   block: # round() tests
     # Round to 0 decimal places
     doAssert round(54.652) ==~ 55.0