Add Random.Bool.weightedBool

elm.json

@@ -6,6 +6,7 @@
     "version": "3.2.0",
     "exposed-modules": [
         "Random.Array",
+        "Random.Bool",
         "Random.Char",
         "Random.Date",
         "Random.Dict",

src/Random/Bool.elm

@@ -0,0 +1,41 @@
+module Random.Bool exposing (weightedBool)
+
+{-| Extra functions for generating Bools.
+
+
+# Values
+
+@docs weightedBool
+
+-}
+
+import Random exposing (Generator)
+
+
+{-| Generates True with probability given by the argument (number 0..1, clamped
+to these bounds if needed)
+
+    weightedBool -0.5 -- always generates False
+
+    weightedBool 0 -- always generates False
+
+    weightedBool 0.25 -- biased coin, generates True 25% of the time
+
+    weightedBool 0.5 -- fair coin, same as Random.Extra.bool
+
+    weightedBool 0.75 -- biased coin, generates True 75% of the time
+
+    weightedBool 1 -- always generates True
+
+    weightedBool 1.5 -- always generates True
+
+-}
+weightedBool : Float -> Generator Bool
+weightedBool probability =
+    let
+        clampedProbability : Float
+        clampedProbability =
+            clamp 0 1 probability
+    in
+    Random.float 0 1
+        |> Random.map (\float -> float <= clampedProbability)