Implement threshold

2 files changed, 41 insertions, 1 deletions

diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index a18584c..12d9130 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -10,7 +10,8 @@ const {
   explode,
   keepHigh,
   keepLow,
-  again
+  again,
+  threshold
 } = require('../src/dice.js')
 
 const defaultNumberRolls = 500
@@ -560,3 +561,25 @@ describe('again', () => {
     })
   })
 })
+
+describe('threshold', () => {
+  describe('8T3d10', () => {
+    const die = threshold(constant(8), d(constant(3), constant(10)))
+
+    testDie(die, {
+      diceCount: 3,
+      average: {
+        average: 0.9
+      },
+      variance: {
+        variance: 0.63
+      },
+      bounds: {
+        low: 0,
+        high: 3,
+        expectLow: true,
+        expectHigh: true
+      }
+    })
+  })
+})
diff --git a/src/dice.js b/src/dice.js
index ef67edf..9bc53d7 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -147,6 +147,22 @@ const again = (die1, die2) => {
   }
 }
 
+const threshold = (die1, die2) => {
+  return () => {
+    const cutoff = roll(die1)
+
+    return die2().map(die => {
+      return () => {
+        if (die() >= cutoff) {
+          return 1
+        } else {
+          return 0
+        }
+      }
+    })
+  }
+}
+
 
 exports.pool = pool
 exports.roll = roll
@@ -161,3 +177,4 @@ exports.explode = explode
 exports.keepHigh = keepHigh
 exports.keepLow = keepLow
 exports.again = again
+exports.threshold = threshold