program = funcDecl*
decl = declspec declarator ("{" compoundStmt | ";")
funcDecl = compoundStmt
declaration = declspec declarator ("=" expr)? ("," declarator ("=" expr)?)*)? ";"
declspec = "int" | "char"
declarator = "*"* ident type-suffix
type-suffix = "(" func-params | "[" num "]" type-suffix | ε
func-params = (param ("," param)*)? ")"
param = declspec declarator
stmt = expr ";" | "{ compoundStmt | returnStmt | ifStmt | whileStmt | forStmt
compoundStmt = (declaration | stmt)* "}"
returnStmt = "return" expr ";"
ifStmt = "if" "(" expr ")" stmt ("else" stmt)?
whileStmt = "while" "(" expr ")" stmt
forStmt = "for" "(" expr? ";" expr? ";" expr? ")" stmt
expr = assign
assign = equality ("=" assign)?
equality = relational ("==" relational | "!=" relational)*
relational = add ("<" add | "<=" add | ">" add | ">=" add)*
add = mul ("+" mul | "-" mul)*
mul = unary ("*" unary | "/" unary)*
unary = ("+" | "-" | "*" | "&") unary | postfix
postfix = primary ("[" expr "]")*
primary = "(" expr ")" | "sizeof" unary | ident func-args? | num | str
func-args = "(" (assign ("," assign)*)? ")"
