subtree(users/wpcarro): docking briefcase at '24f5a642'

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c
git-subtree-split: 24f5a642af
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

users/wpcarro/scratch/facebook/moderate/parser.py

@@ -0,0 +1,37 @@
+class Parser(object):
+    def __init__(self, tokens):
+        self.tokens = tokens
+        self.i = 0
+
+    def prev(self):
+        return self.tokens[self.i - 1]
+
+    def curr(self):
+        return self.tokens[self.i]
+
+    def next(self):
+        return self.tokens[self.i + 1]
+
+    def consume(self):
+        if not self.exhausted():
+            self.i += 1
+            return self.prev()
+
+    def match(self, xs):
+        if not self.exhausted() and self.curr() in xs:
+            self.consume()
+            return True
+        return False
+
+    def expect(self, xs):
+        if not self.match(xs):
+            raise Exception("Expected token \"{}\" but received \"{}\"".format(xs, self.curr()))
+        return self.prev()
+
+    def expect_predicate(self, predicate):
+        if predicate(self.curr()):
+            return self.consume()
+        raise Exception("Expected token \"{}\" to pass predicate, but it did not".format(self.curr()))
+
+    def exhausted(self):
+        return self.i >= len(self.tokens)