diff options
author | David Beazley <dave@dabeaz.com> | 2007-11-28 17:35:25 +0000 |
---|---|---|
committer | David Beazley <dave@dabeaz.com> | 2007-11-28 17:35:25 +0000 |
commit | 051284882c89795552e84813b506f7cd99a094d9 (patch) | |
tree | 158d721550bb2b035fe107b184b22b8ece8d70dc /example/closurecalc/calc.py | |
parent | 1fcdc01f1d188a2df49b53576bf2659f5f323f63 (diff) | |
download | ply-051284882c89795552e84813b506f7cd99a094d9.tar.gz |
new example
Diffstat (limited to 'example/closurecalc/calc.py')
-rw-r--r-- | example/closurecalc/calc.py | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/example/closurecalc/calc.py b/example/closurecalc/calc.py new file mode 100644 index 0000000..7f4bf4f --- /dev/null +++ b/example/closurecalc/calc.py @@ -0,0 +1,131 @@ +# ----------------------------------------------------------------------------- +# calc.py +# +# A calculator parser that makes use of closures. The function make_calculator() +# returns a function that accepts an input string and returns a result. All +# lexing rules, parsing rules, and internal state are held inside the function. +# ----------------------------------------------------------------------------- + +import sys +sys.path.insert(0,"../..") + +# Make a calculator function + +def make_calculator(): + import ply.lex as lex + import ply.yacc as yacc + + # ------- Internal calculator state + + variables = { } # Dictionary of stored variables + + # ------- Calculator tokenizing rules + + tokens = ( + 'NAME','NUMBER', + ) + + literals = ['=','+','-','*','/', '(',')'] + + t_ignore = " \t" + + 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 + + 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 + lexer = lex.lex() + + # ------- Calculator parsing rules + + precedence = ( + ('left','+','-'), + ('left','*','/'), + ('right','UMINUS'), + ) + + def p_statement_assign(p): + 'statement : NAME "=" expression' + variables[p[1]] = p[3] + p[0] = None + + def p_statement_expr(p): + 'statement : expression' + p[0] = 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] = variables[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" + + + # Build the parser + parser = yacc.yacc() + + # ------- Input function + + def input(text): + result = parser.parse(text,lexer=lexer) + return result + + return input + +# Make a calculator object and use it +calc = make_calculator() + +while True: + try: + s = raw_input("calc > ") + except EOFError: + break + r = calc(s) + if r: + print r + + |