initial checkin

1 files changed, 105 insertions, 0 deletions

diff --git a/example/calc/calc.py b/example/calc/calc.py
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+++ b/example/calc/calc.py
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+# -----------------------------------------------------------------------------
+# calc.py
+#
+# A simple calculator with variables.   This is from O'Reilly's
+# "Lex and Yacc", p. 63.
+# -----------------------------------------------------------------------------
+
+import sys
+sys.path.insert(0,"../..")
+
+tokens = (
+    'NAME','NUMBER',
+    )
+
+literals = ['=','+','-','*','/', '(',')']
+
+# Tokens
+
+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", 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()
+
+# 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):
+    print "Syntax error at '%s'" % p.value
+
+import ply.yacc as yacc
+yacc.yacc()
+
+while 1:
+    try:
+        s = raw_input('calc > ')
+    except EOFError:
+        break
+    if not s: continue
+    yacc.parse(s)