From 7efea0582dda35cd7dc0c370ef3b56c84b2f2291 Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Wed, 30 Aug 2017 16:25:34 -0400
Subject: Implement explode under

---
 __tests__/dice.test.js   | 19 +++++++++++++++++++
 __tests__/lexer.test.js  | 10 ++++++++++
 __tests__/parser.test.js | 10 ++++++++++
 index.js                 |  2 ++
 src/dice.js              | 16 ++++++++++++++++
 src/lexer.js             |  1 +
 src/parser.js            |  1 +
 7 files changed, 59 insertions(+)

diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index 12d9130..d4e2802 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -8,6 +8,7 @@ const {
   bonusSubtract,
   negative,
   explode,
+  explodeUnder,
   keepHigh,
   keepLow,
   again,
@@ -483,6 +484,24 @@ describe('exploding dice', () => {
       }
     })
   })
+
+  describe('1e1d6', () => {
+    const die = explodeUnder(constant(1), d(constant(1), constant(6)))
+    testDie(die, {
+      diceCount: 1,
+      average: {
+        average: 4.2
+      },
+      variance: {
+        variance: 2.24
+      },
+      bounds: {
+        low: 2,
+        expectLow: true,
+        high: Infinity
+      }
+    })
+  })
 })
 
 describe('keep', () => {
diff --git a/__tests__/lexer.test.js b/__tests__/lexer.test.js
index 21ae3b0..0336f44 100644
--- a/__tests__/lexer.test.js
+++ b/__tests__/lexer.test.js
@@ -148,6 +148,16 @@ describe('lex', () => {
         { type: 'constant', value: 6 }
       ])
     })
+
+    test('1e1d6', () => {
+      expect(lex('1e1d6')).toEqual([
+        { type: 'constant', value: 1 },
+        { type: 'e' },
+        { type: 'constant', value: 1 },
+        { type: 'd' },
+        { type: 'constant', value: 6 }
+      ])
+    })
   })
 
   describe('keep', () => {
diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index 70ad98d..765388d 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -173,6 +173,16 @@ describe('parse', () => {
         right: { type: 'constant', value: 6 }
       }
     })
+
+    expect(parse('1e1d6')).toEqual({
+      type: 'e',
+      left: { type: 'constant', value: 1 },
+      right: {
+        type: 'd',
+        left: { type: 'constant', value: 1 },
+        right: { type: 'constant', value: 6 }
+      }
+    })
   })
 
   it('parses dice with keep high', () => {
diff --git a/index.js b/index.js
index e117b7c..8c52ad1 100644
--- a/index.js
+++ b/index.js
@@ -9,6 +9,8 @@ const interpret = tree => {
     return D.d(interpret(tree.left), interpret(tree.right))
   case 'E':
     return D.explode(interpret(tree.left), interpret(tree.right))
+  case 'e':
+    return D.explodeUnder(interpret(tree.left), interpret(tree.right))
   case 'K':
     return D.keepHigh(interpret(tree.left), interpret(tree.right))
   case 'k':
diff --git a/src/dice.js b/src/dice.js
index 9bc53d7..e96aca9 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -73,6 +73,21 @@ const explode = (die1, die2) => {
   }
 }
 
+const explodeUnder = (die1, die2) => {
+  return () => {
+    const explodeOn = roll(die1)
+    return die2().map(die => () => {
+      let lastRoll = die()
+      let total = lastRoll
+      while (lastRoll <= explodeOn) {
+        lastRoll = die()
+        total += lastRoll
+      }
+      return total
+    })
+  }
+}
+
 const keepHigh = (die1, die2) => {
   return () => {
     const numberToKeep = roll(die1)
@@ -174,6 +189,7 @@ exports.bonusAdd = bonusAdd
 exports.bonusSubtract = bonusSubtract
 exports.negative = negative
 exports.explode = explode
+exports.explodeUnder = explodeUnder
 exports.keepHigh = keepHigh
 exports.keepLow = keepLow
 exports.again = again
diff --git a/src/lexer.js b/src/lexer.js
index f316147..7eb95b0 100644
--- a/src/lexer.js
+++ b/src/lexer.js
@@ -23,6 +23,7 @@ newLexemeType('minus', '-')
 newLexemeType('(', '\\(')
 newLexemeType(')', '\\)')
 newLexemeType('E', 'E')
+newLexemeType('e', 'e')
 newLexemeType('K', 'K')
 newLexemeType('k', 'k')
 newLexemeType('A', 'A')
diff --git a/src/parser.js b/src/parser.js
index 0201d05..124d686 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -61,6 +61,7 @@ newSymbol('d', (parser) => {
   }
 })
 newDieOperation('E')
+newDieOperation('e')
 newDieOperation('K')
 newDieOperation('k')
 newDieOperation('A')
-- 
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