1 files changed, 134 insertions, 0 deletions
diff --git a/third_party/python/ply/example/optcalc/calc.py b/third_party/python/ply/example/optcalc/calc.py
new file mode 100644
index 0000000000..0c223e5994
--- /dev/null
+++ b/third_party/python/ply/example/optcalc/calc.py
@@ -0,0 +1,134 @@
+# -----------------------------------------------------------------------------
+# calc.py
+#
+# A simple calculator with variables.   This is from O'Reilly's
+# "Lex and Yacc", p. 63.
+# -----------------------------------------------------------------------------
+
+import sys
+sys.path.insert(0, "../..")
+
+if sys.version_info[0] >= 3:
+    raw_input = input
+
+tokens = (
+    'NAME', 'NUMBER',
+    'PLUS', 'MINUS', 'TIMES', 'DIVIDE', 'EQUALS',
+    'LPAREN', 'RPAREN',
+)
+
+# Tokens
+
+t_PLUS = r'\+'
+t_MINUS = r'-'
+t_TIMES = r'\*'
+t_DIVIDE = r'/'
+t_EQUALS = r'='
+t_LPAREN = r'\('
+t_RPAREN = r'\)'
+t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
+
+
+def t_NUMBER(t):
+    r'\d+'
+    try:
+        t.value = int(t.value)
+    except ValueError:
+        print("Integer value too large %s" % t.value)
+        t.value = 0
+    return t
+
+t_ignore = " \t"
+
+
+def t_newline(t):
+    r'\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(optimize=1)
+
+# Parsing rules
+
+precedence = (
+    ('left', 'PLUS', 'MINUS'),
+    ('left', 'TIMES', 'DIVIDE'),
+    ('right', 'UMINUS'),
+)
+
+# dictionary of names
+names = {}
+
+
+def p_statement_assign(t):
+    'statement : NAME EQUALS expression'
+    names[t[1]] = t[3]
+
+
+def p_statement_expr(t):
+    'statement : expression'
+    print(t[1])
+
+
+def p_expression_binop(t):
+    '''expression : expression PLUS expression
+                  | expression MINUS expression
+                  | expression TIMES expression
+                  | expression DIVIDE expression'''
+    if t[2] == '+':
+        t[0] = t[1] + t[3]
+    elif t[2] == '-':
+        t[0] = t[1] - t[3]
+    elif t[2] == '*':
+        t[0] = t[1] * t[3]
+    elif t[2] == '/':
+        t[0] = t[1] / t[3]
+    elif t[2] == '<':
+        t[0] = t[1] < t[3]
+
+
+def p_expression_uminus(t):
+    'expression : MINUS expression %prec UMINUS'
+    t[0] = -t[2]
+
+
+def p_expression_group(t):
+    'expression : LPAREN expression RPAREN'
+    t[0] = t[2]
+
+
+def p_expression_number(t):
+    'expression : NUMBER'
+    t[0] = t[1]
+
+
+def p_expression_name(t):
+    'expression : NAME'
+    try:
+        t[0] = names[t[1]]
+    except LookupError:
+        print("Undefined name '%s'" % t[1])
+        t[0] = 0
+
+
+def p_error(t):
+    if t:
+        print("Syntax error at '%s'" % t.value)
+    else:
+        print("Syntax error at EOF")
+
+import ply.yacc as yacc
+yacc.yacc(optimize=1)
+
+while 1:
+    try:
+        s = raw_input('calc > ')
+    except EOFError:
+        break
+    yacc.parse(s)