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-rw-r--r--third_party/python/ply/example/unicalc/calc.py133
1 files changed, 133 insertions, 0 deletions
diff --git a/third_party/python/ply/example/unicalc/calc.py b/third_party/python/ply/example/unicalc/calc.py
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+++ b/third_party/python/ply/example/unicalc/calc.py
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+# -----------------------------------------------------------------------------
+# 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))