Implement division

8 files changed, 80 insertions, 1 deletions

diff --git a/README.md b/README.md
index aecf2fe..c140d91 100644
--- a/README.md
+++ b/README.md
@@ -81,6 +81,7 @@ The parser recognizes the following grammar:
           | Die ' + ' Die
           | Die ' - ' Die
           | Die ' * ' Die
+          | Die ' / ' Die
           | Die '+' Die
           | Die '-' Die
           | '-' Die
@@ -109,6 +110,8 @@ Semantics are defined in terms of the `pool` function.
 * `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` generates a dicepool with a single value - the result of integer
+  division 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)`.
@@ -140,7 +143,10 @@ Semantics are defined in terms of the `pool` function.
 
 Additionally:
 
-* The binary arithmetic operations (` + `, ` - `) are left associative.
+* The binary arithmetic operations (` + `, ` - `, ` * `, ` / `) are left
+  associative.
+* The binary arithmetic operations bind as expected (multiplication and division
+  bind stronger than addition and subtraction).
 * The bonus operations (`+`, `-`) are left associative. They bind stronger than
   arithmetic operations.
 * The die operations (`d`, `E`, `K`, etc.) are right associative (`1d2d3` is
diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index 4e89031..d397d4c 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -5,6 +5,7 @@ const {
   add,
   subtract,
   multiply,
+  divide,
   bonusAdd,
   bonusSubtract,
   negative,
@@ -338,6 +339,27 @@ describe('multiply', () => {
   })
 })
 
+describe('divide', () => {
+  describe('1d8 / 2', () => {
+    const die = divide(d(constant(1), constant(8)), constant(2))
+    testDie(die, {
+      diceCount: 1,
+      average: {
+        average: 2
+      },
+      variance: {
+        variance: 1.5
+      },
+      bounds: {
+        low: 0,
+        high: 4,
+        expectLow: true,
+        expectHigh: true
+      }
+    })
+  })
+})
+
 
 describe('bonusAdd', () => {
   describe('1d20+3', () => {
diff --git a/__tests__/lexer.test.js b/__tests__/lexer.test.js
index db7ab50..0c615d5 100644
--- a/__tests__/lexer.test.js
+++ b/__tests__/lexer.test.js
@@ -121,6 +121,30 @@ describe('lex', () => {
     })
   })
 
+  describe('lexes division', () => {
+    it('1d6 / 1d4', () => {
+      expect(lex('1d6 / 1d4')).toEqual([
+        { type: 'constant', value: 1 },
+        { type: 'd' },
+        { type: 'constant', value: 6 },
+        { type: 'bigDivide' },
+        { 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: 'bigDivide' },
+        { 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 5d4288d..bef11c5 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -113,6 +113,22 @@ describe('parse', () => {
     })
   })
 
+  it('parses dice division', () => {
+    expect(parse('1d6 / 2d8')).toEqual({
+      type: 'divide',
+      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',
diff --git a/index.js b/index.js
index 9a4534b..37883cc 100644
--- a/index.js
+++ b/index.js
@@ -29,6 +29,8 @@ const interpret = tree => {
     return D.subtract(interpret(tree.left), interpret(tree.right))
   case 'multiply':
     return D.multiply(interpret(tree.left), interpret(tree.right))
+  case 'divide':
+    return D.divide(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 abe3c4b..d47455e 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -50,6 +50,12 @@ const multiply = (die1, die2) => {
   }
 }
 
+const divide = (die1, die2) => {
+  return () => {
+    return [() => Math.floor(roll(die1) / roll(die2))]
+  }
+}
+
 const bonusAdd = (die1, die2) => {
   return () => {
     return die1().map(die => {
@@ -194,6 +200,7 @@ exports.d = d
 exports.add = add
 exports.subtract = subtract
 exports.multiply = multiply
+exports.divide = divide
 exports.bonusAdd = bonusAdd
 exports.bonusSubtract = bonusSubtract
 exports.negative = negative
diff --git a/src/lexer.js b/src/lexer.js
index c3eec8a..59fba16 100644
--- a/src/lexer.js
+++ b/src/lexer.js
@@ -19,6 +19,7 @@ newLexemeType('d', 'd')
 newLexemeType('bigPlus', ' \\+ ' )
 newLexemeType('bigMinus', ' - ')
 newLexemeType('bigTimes', ' \\* ')
+newLexemeType('bigDivide', ' / ')
 newLexemeType('plus', '\\+')
 newLexemeType('minus', '-')
 newLexemeType('(', '\\(')
diff --git a/src/parser.js b/src/parser.js
index 1a1e5d4..fd0fd59 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -72,6 +72,7 @@ newDieOperation('t')
 newInfix('bigPlus', 20, { type: 'add' })
 newInfix('bigMinus', 20, { type: 'subtract' })
 newInfix('bigTimes', 23, { type: 'multiply' })
+newInfix('bigDivide', 23, { type: 'divide' })
 newInfix('plus', 25, { type: 'bonusAdd' })
 newInfix('minus', 25, { type: 'bonusSubtract' })
 newSymbol('minus', (parser) => {