Implement multiplication

8 files changed, 103 insertions, 0 deletions

diff --git a/README.md b/README.md
index d5cbbbc..aecf2fe 100644
--- a/README.md
+++ b/README.md
@@ -80,6 +80,7 @@ The parser recognizes the following grammar:
           | 'd' Die
           | Die ' + ' Die
           | Die ' - ' Die
+          | Die ' * ' Die
           | Die '+' Die
           | Die '-' Die
           | '-' Die
@@ -106,6 +107,8 @@ Semantics are defined in terms of the `pool` function.
   `D`.
 * `-D` returns the opposites of values generated by `D`.
 * `D - E` is equivalent to `D + (-E)`.
+* `D * E` generates a dicepool with a single value - the produc of `roll(D)` and
+  `roll(E)`.
 * `D+E` is the additive bonus operation. For each die in `D`'s pool, the die is
   rolled and `roll(E)` is added to its result.
 * `D-E` is equivalent to `D+(-E)`.
diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index caba0a9..4e89031 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -4,6 +4,7 @@ const {
   d,
   add,
   subtract,
+  multiply,
   bonusAdd,
   bonusSubtract,
   negative,
@@ -316,6 +317,28 @@ describe('subtract', () => {
   })
 })
 
+describe('multiply', () => {
+  describe('1d6 * 3', () => {
+    const die = multiply(d(constant(1), constant(6)), constant(3))
+    testDie(die, {
+      diceCount: 1,
+      average: {
+        average: 10.5
+      },
+      variance: {
+        variance: 26.25
+      },
+      bounds: {
+        low: 3,
+        high: 18,
+        expectLow: true,
+        expectHigh: true
+      }
+    })
+  })
+})
+
+
 describe('bonusAdd', () => {
   describe('1d20+3', () => {
     const die = bonusAdd(d(constant(1), constant(20)), constant(3))
diff --git a/__tests__/lexer.test.js b/__tests__/lexer.test.js
index b51c0f9..db7ab50 100644
--- a/__tests__/lexer.test.js
+++ b/__tests__/lexer.test.js
@@ -97,6 +97,30 @@ describe('lex', () => {
     })
   })
 
+  describe('lexes multiplication', () => {
+    it('1d6 * 1d4', () => {
+      expect(lex('1d6 * 1d4')).toEqual([
+        { type: 'constant', value: 1 },
+        { type: 'd' },
+        { type: 'constant', value: 6 },
+        { type: 'bigTimes' },
+        { type: 'constant', value: 1 },
+        { type: 'd' },
+        { type: 'constant', value: 4 }
+      ])
+    })
+
+    it('2d17 * 4', () => {
+      expect(lex('2d17 * 4')).toEqual([
+        { type: 'constant', value: 2 },
+        { type: 'd' },
+        { type: 'constant', value: 17 },
+        { type: 'bigTimes' },
+        { type: 'constant', value: 4 }
+      ])
+    })
+  })
+
   describe('lexes parentheses', () => {
     it('(1d6)d6', () => {
       expect(lex('(1d6)d6')).toEqual([
diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index 6e575b6..5d4288d 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -97,6 +97,22 @@ describe('parse', () => {
     })
   })
 
+  it('parses dice multiplication', () => {
+    expect(parse('1d6 * 2d8')).toEqual({
+      type: 'multiply',
+      left: {
+        type: 'd',
+        left: { type: 'constant', value: 1 },
+        right: { type: 'constant', value: 6 }
+      },
+      right: {
+        type: 'd',
+        left: { type: 'constant', value: 2 },
+        right: { type: 'constant', value: 8 }
+      }
+    })
+  })
+
   it('parses additive bonuses', () => {
     expect(parse('3d4+1')).toEqual({
       type: 'bonusAdd',
@@ -282,4 +298,30 @@ describe('parse', () => {
       })
     })
   })
+
+  describe('order of operations', () => {
+    test('2 * 3 + 4', () => {
+      expect(parse('2 * 3 + 4')).toEqual({
+        type: 'add',
+        left: {
+          type: 'multiply',
+          left: { type: 'constant', value: 2 },
+          right: { type: 'constant', value: 3 },
+        },
+        right: { type: 'constant', value: 4 },
+      })
+    })
+
+    test('2 + 3 * 4', () => {
+      expect(parse('2 + 3 * 4')).toEqual({
+        type: 'add',
+        left: { type: 'constant', value: 2 },
+        right: {
+          type: 'multiply',
+          left: { type: 'constant', value: 3 },
+          right: { type: 'constant', value: 4 },
+        }
+      })
+    })
+  })
 })
diff --git a/index.js b/index.js
index 1851a77..9a4534b 100644
--- a/index.js
+++ b/index.js
@@ -27,6 +27,8 @@ const interpret = tree => {
     return D.add(interpret(tree.left), interpret(tree.right))
   case 'subtract':
     return D.subtract(interpret(tree.left), interpret(tree.right))
+  case 'multiply':
+    return D.multiply(interpret(tree.left), interpret(tree.right))
   case 'negative':
     return D.negative(interpret(tree.value))
   case 'bonusAdd':
diff --git a/src/dice.js b/src/dice.js
index 828a772..abe3c4b 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -44,6 +44,12 @@ const subtract = (die1, die2) => {
   }
 }
 
+const multiply = (die1, die2) => {
+  return () => {
+    return [() => roll(die1) * roll(die2)]
+  }
+}
+
 const bonusAdd = (die1, die2) => {
   return () => {
     return die1().map(die => {
@@ -187,6 +193,7 @@ exports.constant = constant
 exports.d = d
 exports.add = add
 exports.subtract = subtract
+exports.multiply = multiply
 exports.bonusAdd = bonusAdd
 exports.bonusSubtract = bonusSubtract
 exports.negative = negative
diff --git a/src/lexer.js b/src/lexer.js
index ba3d3a5..c3eec8a 100644
--- a/src/lexer.js
+++ b/src/lexer.js
@@ -18,6 +18,7 @@ newValueLexeme('constant', '\\d+', Number)
 newLexemeType('d', 'd')
 newLexemeType('bigPlus', ' \\+ ' )
 newLexemeType('bigMinus', ' - ')
+newLexemeType('bigTimes', ' \\* ')
 newLexemeType('plus', '\\+')
 newLexemeType('minus', '-')
 newLexemeType('(', '\\(')
diff --git a/src/parser.js b/src/parser.js
index adb4b9b..1a1e5d4 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -71,6 +71,7 @@ newDieOperation('t')
 
 newInfix('bigPlus', 20, { type: 'add' })
 newInfix('bigMinus', 20, { type: 'subtract' })
+newInfix('bigTimes', 23, { type: 'multiply' })
 newInfix('plus', 25, { type: 'bonusAdd' })
 newInfix('minus', 25, { type: 'bonusSubtract' })
 newSymbol('minus', (parser) => {