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# oc.py
#
# A subset-C parser, (BNF taken from 1996 International Obfuscated C Code Contest)
#
# Copyright, 2010, Paul McGuire
#
"""
http://www.ioccc.org/1996/august.hint
The following is a description of the OC grammar:
OC grammar
==========
Terminals are in quotes, () is used for bracketing.
program: decl*
decl: vardecl
fundecl
vardecl: type NAME ;
type NAME "[" INT "]" ;
fundecl: type NAME "(" args ")" "{" body "}"
args: /*empty*/
( arg "," )* arg
arg: type NAME
body: vardecl* stmt*
stmt: ifstmt
whilestmt
dowhilestmt
"return" expr ";"
expr ";"
"{" stmt* "}"
";"
ifstmt: "if" "(" expr ")" stmt
"if" "(" expr ")" stmt "else" stmt
whilestmt: "while" "(" expr ")" stmt
dowhilestmt: "do" stmt "while" "(" expr ")" ";"
expr: expr binop expr
unop expr
expr "[" expr "]"
"(" expr ")"
expr "(" exprs ")"
NAME
INT
CHAR
STRING
exprs: /*empty*/
(expr ",")* expr
binop: "+" | "-" | "*" | "/" | "%" |
"=" |
"<" | "==" | "!="
unop: "!" | "-" | "*"
type: "int" stars
"char" stars
stars: "*"*
"""
from pyparsing import *
LPAR,RPAR,LBRACK,RBRACK,LBRACE,RBRACE,SEMI,COMMA = map(Suppress, "()[]{};,")
INT, CHAR, WHILE, DO, IF, ELSE, RETURN = map(Keyword,
"int char while do if else return".split())
NAME = Word(alphas+"_", alphanums+"_")
integer = Regex(r"[+-]?\d+")
char = Regex(r"'.'")
string_ = dblQuotedString
TYPE = Group((INT | CHAR) + ZeroOrMore("*"))
expr = Forward()
operand = NAME | integer | char | string_
expr << (infixNotation(operand,
[
(oneOf('! - *'), 1, opAssoc.RIGHT),
(oneOf('++ --'), 1, opAssoc.RIGHT),
(oneOf('++ --'), 1, opAssoc.LEFT),
(oneOf('* / %'), 2, opAssoc.LEFT),
(oneOf('+ -'), 2, opAssoc.LEFT),
(oneOf('< == > <= >= !='), 2, opAssoc.LEFT),
(Regex(r'=[^=]'), 2, opAssoc.LEFT),
]) +
Optional( LBRACK + expr + RBRACK |
LPAR + Group(Optional(delimitedList(expr))) + RPAR )
)
stmt = Forward()
ifstmt = IF - LPAR + expr + RPAR + stmt + Optional(ELSE + stmt)
whilestmt = WHILE - LPAR + expr + RPAR + stmt
dowhilestmt = DO - stmt + WHILE + LPAR + expr + RPAR + SEMI
returnstmt = RETURN - expr + SEMI
stmt << Group( ifstmt |
whilestmt |
dowhilestmt |
returnstmt |
expr + SEMI |
LBRACE + ZeroOrMore(stmt) + RBRACE |
SEMI)
vardecl = Group(TYPE + NAME + Optional(LBRACK + integer + RBRACK)) + SEMI
arg = Group(TYPE + NAME)
body = ZeroOrMore(vardecl) + ZeroOrMore(stmt)
fundecl = Group(TYPE + NAME + LPAR + Optional(Group(delimitedList(arg))) + RPAR +
LBRACE + Group(body) + RBRACE)
decl = fundecl | vardecl
program = ZeroOrMore(decl)
program.ignore(cStyleComment)
# set parser element names
for vname in ("ifstmt whilestmt dowhilestmt returnstmt TYPE "
"NAME fundecl vardecl program arg body stmt".split()):
v = vars()[vname]
v.setName(vname)
#~ for vname in "fundecl stmt".split():
#~ v = vars()[vname]
#~ v.setDebug()
test = r"""
/* A factorial program */
int
putstr(char *s)
{
while(*s)
putchar(*s++);
}
int
fac(int n)
{
if (n == 0)
return 1;
else
return n*fac(n-1);
}
int
putn(int n)
{
if (9 < n)
putn(n / 10);
putchar((n%10) + '0');
}
int
facpr(int n)
{
putstr("factorial ");
putn(n);
putstr(" = ");
putn(fac(n));
putstr("\n");
}
int
main()
{
int i;
i = 0;
while(i < 10)
facpr(i++);
return 0;
}
"""
ast = program.parseString(test, parseAll=True)
ast.pprint()
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