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-rw-r--r--README.md1
-rw-r--r--__tests__/dice.test.js43
-rw-r--r--__tests__/parser.test.js12
-rw-r--r--index.js2
-rw-r--r--src/dice.js10
-rw-r--r--src/parser.js1
6 files changed, 68 insertions, 1 deletions
diff --git a/README.md b/README.md
index 86db32b..e868675 100644
--- a/README.md
+++ b/README.md
@@ -102,6 +102,7 @@ Semantics are defined in terms of the `pool` function.
* `D - E` is equivalent to `D + (-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)`.
* `DEF` (here `E` is the literal symbol `E`, `D` and `F` are dice expressions)
is an "exploding die." First `D` is rolled. Now each die in the dice pool
generated by `F` is rolled repeatedly until it rolls something less than the
diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index 3073fee..6ff86e7 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -8,7 +8,8 @@ const {
explode,
keepHigh,
keepLow,
- bonusAdd
+ bonusAdd,
+ bonusSubtract
} = require('../src/dice.js')
const defaultNumberRolls = 500
@@ -493,3 +494,43 @@ describe('bonusAdd', () => {
})
})
})
+
+describe('bonusSubtract', () => {
+ describe('1d20-3', () => {
+ const die = bonusSubtract(d(constant(1), constant(20)), constant(3))
+ testDie(die, {
+ diceCount: 1,
+ average: {
+ average: 7.5
+ },
+ variance: {
+ variance: 33.25
+ },
+ bounds: {
+ low: -2,
+ high: 17,
+ expectLow: true,
+ expectHigh: true
+ }
+ })
+ })
+
+ describe('3d4-1', () => {
+ const die = bonusSubtract(d(constant(3), constant(4)), constant(1))
+ testDie(die, {
+ diceCount: 3,
+ average: {
+ average: 4.5
+ },
+ variance: {
+ variance: 3.75
+ },
+ bounds: {
+ low: 0,
+ high: 9,
+ expectLow: true,
+ expectHigh: true
+ }
+ })
+ })
+})
diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index 873972b..54e1da7 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -163,6 +163,18 @@ describe('parse', () => {
})
})
+ it('parses negative bonuses', () => {
+ expect(parse('3d4-1')).toEqual({
+ type: 'bonusSubtract',
+ left: {
+ type: 'd',
+ left: { type: 'constant', value: 3 },
+ right: { type: 'constant', value: 4 }
+ },
+ right: { type: 'constant', value: 1 }
+ })
+ })
+
describe('parsing parentheses', () => {
test('(1d6)d6', () => {
expect(parse('(1d6)d6')).toEqual({
diff --git a/index.js b/index.js
index 980c6b4..895656d 100644
--- a/index.js
+++ b/index.js
@@ -21,6 +21,8 @@ const interpret = tree => {
return D.negative(interpret(tree.value))
case 'bonusAdd':
return D.bonusAdd(interpret(tree.left), interpret(tree.right))
+ case 'bonusSubtract':
+ return D.bonusSubtract(interpret(tree.left), interpret(tree.right))
}
}
diff --git a/src/dice.js b/src/dice.js
index becf7dc..58467c4 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -102,6 +102,15 @@ const bonusAdd = (die1, die2) => {
}
}
+const bonusSubtract = (die1, die2) => {
+ const negative2 = negative(die2)
+ return () => {
+ return die1().map(die => {
+ return () => die() + roll(negative2)
+ })
+ }
+}
+
exports.pool = pool
exports.roll = roll
exports.constant = constant
@@ -113,3 +122,4 @@ exports.explode = explode
exports.keepHigh = keepHigh
exports.keepLow = keepLow
exports.bonusAdd = bonusAdd
+exports.bonusSubtract = bonusSubtract
diff --git a/src/parser.js b/src/parser.js
index 48de2ab..244cdd1 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -66,6 +66,7 @@ newDieOperation('k')
newInfix('bigPlus', 20, { type: 'add' })
newInfix('plus', 20, { type: 'bonusAdd' })
+newInfix('minus', 20, { type: 'bonusSubtract' })
newInfix('bigMinus', 20, { type: 'subtract' })
newSymbol('minus', (parser) => {
return {