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# oc.py
#
# A subset-C parser, (BNF taken from 1996 International Obfuscated C Code Contest)
#
# Copyright, 2010, Paul McGuire
#
"""
https://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 *
ParserElement.enablePackrat()
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()
func_call = Group(NAME + LPAR + Group(Optional(delimitedList(expr))) + RPAR)
operand = func_call | 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()
def main():
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;
if(a() == 1){}
while(i < 10)
facpr(i++);
return 0;
}
"""
ast = program.parseString(test, parseAll=True)
ast.pprint()
if __name__ == "__main__":
main()