# 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()