Switch isFinite to isInfinite and improve documentation

libraries/Basics.elm

@@ -30,9 +30,6 @@ are your tuples so big?
 # Number Conversions
 @docs round, floor, ceiling, truncate, toFloat
 
-# Floating Point Checks
-@docs isNaN, isFinite
-
 # Angle Conversions
 All angle conversions result in “standard Elm angles”
 which happen to be radians.
@@ -42,6 +39,9 @@ which happen to be radians.
 # Polar Coordinates
 @docs toPolar, fromPolar
 
+# Floating Point Checks
+@docs isNaN, isInfinite
+
 # Tuples
 @docs fst, snd
 
@@ -274,17 +274,30 @@ ceiling = Native.Basics.ceiling
 toFloat : Int -> Float
 toFloat = Native.Basics.toFloat
 
-{- | Determines whether a float is an undefined or unrepresentable number,
-such as 0/0. NaN stands for *not a number*.
+{- | Determines whether a float is an undefined or unrepresentable number.
+NaN stands for *not a number* and it is [a standardized part of floating point
+numbers](http://en.wikipedia.org/wiki/NaN).
+
+      isNaN (0/0)     == True
+      isNaN (sqrt -1) == True
+      isNaN (1/0)     == False  -- infinity is a number
+      isNaN 1         == False
 -}
 isNaN : Float -> Bool
 isNaN = Native.Basics.isNaN
 
-{- | Determines whether a float is finite. Positive and negative infinity are
-valid floating point numbers, created by computations like `1/0` and `-1/0`.
+{- | Determines whether a float is positive or negative infinity.
+
+      isInfinite (0/0)     == False
+      isInfinite (sqrt -1) == False
+      isInfinite (1/0)     == True
+      isInfinite 1         == False
+
+Notice that NaN is not infinite! For float `n` to be finite implies that
+`not (isInfinite n || isNaN n)` evaluates to `True`.
 -}
-isFinite : Float -> Bool
-isFinite = Native.Basics.isFinite
+isInfinite : Float -> Bool
+isInfinite = Native.Basics.isInfinite
 
 -- Function Helpers
 

libraries/Native/Basics.js

@@ -19,6 +19,7 @@ Elm.Native.Basics.make = function(elm) {
       return Utils.cmp(n,lo) < 0 ? lo : Utils.cmp(n,hi) > 0 ? hi : n; }
   function xor(a,b) { return a !== b; }
   function not(b) { return !b; }
+  function isInfinite(n) { return n === Infinity || n === -Infinity }
 
   function truncate(n) { return n|0; }
 
@@ -54,7 +55,7 @@ Elm.Native.Basics.make = function(elm) {
       round:Math.round,
       toFloat:function(x) { return x; },
       isNaN:isNaN,
-      isFinite:isFinite
+      isInfinite:isInfinite
   };
 
   return elm.Native.Basics.values = basics;