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Edit: /opt/gsutil/third_party/pyparsing/examples/oc.py

# 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

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()

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