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diff --git a/parser/parser.py b/parser/parser.py
index cf463da..dc562dd 100644
--- a/parser/parser.py
+++ b/parser/parser.py
@@ -1,110 +1,54 @@
-# Parse query
+import os
+from parsimonious import Grammar, NodeVisitor
 
-from ply import lex, yacc
 
-literals = '()'
+# cache
+_grammar = None
 
-tokens = ('NAME', 'AND_OP', 'OR_OP', 'NOT_OP', 'SP1')
 
-t_NAME = '([a-z][a-z0-9_]*)|AND|OR|NOT'
+def load_grammar():
+    global _grammar
+    parser_dir = os.path.dirname(__file__)
+    with open(os.path.join(parser_dir, 'grammar.ebnf'), 'rt') as grammar_file:
+        grammar_text = grammar_file.read()
+    _grammar = Grammar(grammar_text)
 
-t_AND_OP = '&'
 
-t_OR_OP = r'\|'
+def parse(input):
+    if _grammar is None:
+        load_grammar()
+    return _grammar.parse(input)
 
-t_NOT_OP = '!'
 
-t_SP1 = '[ \t]+'
-
-def t_error(t):
-    """Avoid warnings on stderr"""
-
-lexer = lex.lex()
-
-def p_expression_name(p):
-    """expression : NAME"""
-    p[0] = ('NAME', p[1])
-
-def p_expression_and_and(p):
-    """expression : expression SP0 AND_OP AND_OP SP0 expression"""
-    p[0] = ('AND', p[1], p[6])
-
-def p_expression_and(p):
-    """expression : expression SP0 AND_OP SP0 expression"""
-    p[0] = ('AND', p[1], p[5])
-
-def p_expression_op_word(p):
-    """expression : l_expression op_word r_expression"""
-    if p[2] in ('AND', 'and'):
-        p[0] = ('AND', p[1], p[3])
-    elif p[2] in ('OR', 'or'):
-        p[0] = ('OR', p[1], p[3])
-
-def p_expression_or_or(p):
-    """expression : expression SP0 OR_OP OR_OP SP0 expression"""
-    p[0] = ('OR', p[1], p[6])
-
-def p_expression_or(p):
-    """expression : expression SP0 OR_OP SP0 expression"""
-    p[0] = ('OR', p[1], p[5])
-
-def p_expression_not(p):
-    """expression : NOT_OP SP0 expression"""
-    p[0] = ('NOT', p[3])
+def cleanup_children(visited_children):
+    children = [c for c in visited_children if c]
+    if len(children) == 1:
+        return children[0]
+    else:
+        return children
 
-def p_expression_in_parens(p):
-    """expression : expression_parens"""
-    p[0] = p[1]
 
-def p_l_expression(p):
-    """l_expression : expression_parens
-                    | expression SP1
-    """
-    if len(p) == 2:
-        p[0] = p[1]
-    elif len(p) == 3:
-        p[0] = p[1]
-    else:
-        raise ValueError(p)
-
-def p_r_expression(p):
-    """r_expression : expression_parens
-                    | SP1 expression
-    """
-    if len(p) == 2:
-        p[0] = p[1]
-    elif len(p) == 3:
-        p[0] = p[2]
-    else:
-        raise ValueError(p)
+class Compiler(NodeVisitor):
+    def generic_visit(self, node, visited_children):
+        return cleanup_children(visited_children)
 
-def p_expression_parens(p):
-    """expression_parens : '(' SP0 expression SP0 ')'"""
-    p[0] = ('PARENS', p[3])
+    def visit_or_expression(self, node, visited_children):
+        return ('OR', visited_children[0], visited_children[2])
 
-def p_op_word(p):
-    """op_word : NAME"""
-    if p[1] in ('AND', 'and', 'OR', 'or'):
-        p[0] = p[1]
-    else:
-        raise SyntaxError
+    def visit_and_expression(self, node, visited_children):
+        return ('AND', visited_children[0], visited_children[2])
 
-def p_SP0(p):
-    """SP0 : SP1
-           | empty
-    """
+    def visit_not_expression(self, node, visited_children):
+        return ('NOT', visited_children[2])
 
-def p_empty(p):
-    """empty :"""
+    def visit_parens_expression(self, node, visited_children):
+        return ('PARENS', visited_children[2])
 
-def p_error(p):
-    """Avoid warnings on stderr"""
-    yacc.restart()
+    def visit_name(self, node, visited_children):
+        return ('NAME', node.text)
 
-precedence = (
-    ('left', 'OR_OP'),
-    ('left', 'AND_OP'),
-    ('right', 'NOT_OP'),
-)
 
-parser = yacc.yacc()
+def compile(tree):
+    if isinstance(tree, str):
+        tree = parse(tree)
+    return Compiler().visit(tree)