From de517d06737f77a0cfc818c159b388b4e0c4d6b1 Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Fri, 14 Jul 2017 23:35:23 -0400
Subject: Lex and parse negatives

---
 __tests__/parser.test.js | 18 ++++++++++++++++++
 src/parser.js            | 16 ++++++++++++++--
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index a741007..74ca442 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -73,6 +73,24 @@ describe('parse', () => {
     })
   })
 
+  it('parses negatives', () => {
+    expect(parse('-1 + (-(2d6))')).toEqual({
+      type: 'add',
+      left: {
+        type: 'negative',
+        value: { type: 'constant', value: 1 }
+      },
+      right: {
+        type: 'negative',
+        value: {
+          type: 'd',
+          left: { type: 'constant', value: 2 },
+          right: { type: 'constant', value: 6 }
+        }
+      }
+    })
+  })
+
   describe('parsing parentheses', () => {
     test('(1d6)d6', () => {
       expect(parse('(1d6)d6')).toEqual({
diff --git a/src/parser.js b/src/parser.js
index 9f2c6ac..5b9b718 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -40,7 +40,12 @@ newSymbol('+', null, 20, (left, parser) => {
   }
 })
 
-newSymbol('-', null, 20, (left, parser) => {
+newSymbol('-', (parser) => {
+  return {
+    type: 'negative',
+    value: parser.expression(40)
+  }
+}, 20, (left, parser) => {
   return {
     type: 'subtract',
     left: left,
@@ -56,10 +61,17 @@ const newParser = (tokens) => {
     currentToken: 0,
     token: function() { return this.tokens[this.currentToken] },
     advanceToken: function() { this.currentToken++ },
+    match: function(token) {
+      if (this.token().type === token) {
+        this.advanceToken()
+      } else {
+        throw 'error'
+      }
+    },
     expression: function(rbp) {
       let symbol = this.token()
-      let left = symbol.nud()
       this.advanceToken()
+      let left = symbol.nud(this)
 
       while (rbp < this.token().lbp) {
         symbol = this.token()
-- 
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