Create a top-level "third_party" directory

This directory now contains third_party software that is vendored into
the Servo source tree. The idea is that it would eventually hold
webrender and other crates from mozilla-central as well with a standard
patch management approach for each.

third_party/ply/example/unicalc/calc.py

@@ -0,0 +1,133 @@
+# -----------------------------------------------------------------------------
+# calc.py
+#
+# A simple calculator with variables.   This is from O'Reilly's
+# "Lex and Yacc", p. 63.
+#
+# This example uses unicode strings for tokens, docstrings, and input.
+# -----------------------------------------------------------------------------
+
+import sys
+sys.path.insert(0, "../..")
+
+tokens = (
+    'NAME', 'NUMBER',
+    'PLUS', 'MINUS', 'TIMES', 'DIVIDE', 'EQUALS',
+    'LPAREN', 'RPAREN',
+)
+
+# Tokens
+
+t_PLUS = ur'\+'
+t_MINUS = ur'-'
+t_TIMES = ur'\*'
+t_DIVIDE = ur'/'
+t_EQUALS = ur'='
+t_LPAREN = ur'\('
+t_RPAREN = ur'\)'
+t_NAME = ur'[a-zA-Z_][a-zA-Z0-9_]*'
+
+
+def t_NUMBER(t):
+    ur'\d+'
+    try:
+        t.value = int(t.value)
+    except ValueError:
+        print "Integer value too large", t.value
+        t.value = 0
+    return t
+
+t_ignore = u" \t"
+
+
+def t_newline(t):
+    ur'\n+'
+    t.lexer.lineno += t.value.count("\n")
+
+
+def t_error(t):
+    print "Illegal character '%s'" % t.value[0]
+    t.lexer.skip(1)
+
+# Build the lexer
+import ply.lex as lex
+lex.lex()
+
+# Parsing rules
+
+precedence = (
+    ('left', 'PLUS', 'MINUS'),
+    ('left', 'TIMES', 'DIVIDE'),
+    ('right', 'UMINUS'),
+)
+
+# dictionary of names
+names = {}
+
+
+def p_statement_assign(p):
+    'statement : NAME EQUALS expression'
+    names[p[1]] = p[3]
+
+
+def p_statement_expr(p):
+    'statement : expression'
+    print p[1]
+
+
+def p_expression_binop(p):
+    '''expression : expression PLUS expression
+                  | expression MINUS expression
+                  | expression TIMES expression
+                  | expression DIVIDE expression'''
+    if p[2] == u'+':
+        p[0] = p[1] + p[3]
+    elif p[2] == u'-':
+        p[0] = p[1] - p[3]
+    elif p[2] == u'*':
+        p[0] = p[1] * p[3]
+    elif p[2] == u'/':
+        p[0] = p[1] / p[3]
+
+
+def p_expression_uminus(p):
+    'expression : MINUS expression %prec UMINUS'
+    p[0] = -p[2]
+
+
+def p_expression_group(p):
+    'expression : LPAREN expression RPAREN'
+    p[0] = p[2]
+
+
+def p_expression_number(p):
+    'expression : NUMBER'
+    p[0] = p[1]
+
+
+def p_expression_name(p):
+    'expression : NAME'
+    try:
+        p[0] = names[p[1]]
+    except LookupError:
+        print "Undefined name '%s'" % p[1]
+        p[0] = 0
+
+
+def p_error(p):
+    if p:
+        print "Syntax error at '%s'" % p.value
+    else:
+        print "Syntax error at EOF"
+
+import ply.yacc as yacc
+yacc.yacc()
+
+while 1:
+    try:
+        s = raw_input('calc > ')
+    except EOFError:
+        break
+    if not s:
+        continue
+    yacc.parse(unicode(s))