1 files changed, 129 insertions, 0 deletions
diff --git a/third_party/python/ply/example/calcdebug/calc.py b/third_party/python/ply/example/calcdebug/calc.py
new file mode 100644
index 0000000000..06831e2ca5
--- /dev/null
+++ b/third_party/python/ply/example/calcdebug/calc.py
@@ -0,0 +1,129 @@
+# -----------------------------------------------------------------------------
+# calc.py
+#
+# This example shows how to run the parser in a debugging mode
+# with output routed to a logging object.
+# -----------------------------------------------------------------------------
+
+import sys
+sys.path.insert(0, "../..")
+
+if sys.version_info[0] >= 3:
+    raw_input = input
+
+tokens = (
+    'NAME', 'NUMBER',
+)
+
+literals = ['=', '+', '-', '*', '/', '(', ')']
+
+# Tokens
+
+t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
+
+
+def t_NUMBER(t):
+    r'\d+'
+    t.value = int(t.value)
+    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()
+
+# Parsing rules
+
+precedence = (
+    ('left', '+', '-'),
+    ('left', '*', '/'),
+    ('right', 'UMINUS'),
+)
+
+# dictionary of names
+names = {}
+
+
+def p_statement_assign(p):
+    'statement : NAME "=" expression'
+    names[p[1]] = p[3]
+
+
+def p_statement_expr(p):
+    'statement : expression'
+    print(p[1])
+
+
+def p_expression_binop(p):
+    '''expression : expression '+' expression
+                  | expression '-' expression
+                  | expression '*' expression
+                  | expression '/' expression'''
+    if p[2] == '+':
+        p[0] = p[1] + p[3]
+    elif p[2] == '-':
+        p[0] = p[1] - p[3]
+    elif p[2] == '*':
+        p[0] = p[1] * p[3]
+    elif p[2] == '/':
+        p[0] = p[1] / p[3]
+
+
+def p_expression_uminus(p):
+    "expression : '-' expression %prec UMINUS"
+    p[0] = -p[2]
+
+
+def p_expression_group(p):
+    "expression : '(' expression ')'"
+    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()
+
+import logging
+logging.basicConfig(
+    level=logging.INFO,
+    filename="parselog.txt"
+)
+
+while 1:
+    try:
+        s = raw_input('calc > ')
+    except EOFError:
+        break
+    if not s:
+        continue
+    yacc.parse(s, debug=logging.getLogger())