expr_t parse_add_expr(tokenizer_t t){
expr_t expr_left, expr_right;
expr_left = parse_mult_expr(t);
struct token tok = cur_tok(t);
while(tok.kind == TOK_PLUS || tok.kind == TOK_MINUS){
eat_it(t, TOK_ANY); // なんでも食べる
expr_right = parse_mult_expr(t);
expr_left = mk_expr_bin_op(t->filename, t->line,
(tok.kind == TOK_PLUS) ? op_kind_bin_plus : op_kind_bin_minus // +, - のどちらかしかない
, expr_left, expr_right); // left にたたんでいく
tok = cur_tok(t);
}
return expr_left;
}
// expr ::= expr '+' multiplicative expr
// expr '-' multiplicative expr
// multiplicative expr
//
// or
// expr ::= multi_expr (add-rest)
Expr*
parse_add_expr(Parser& p, Token_stream& ts)
{
// parse primary expressions
if (Expr* e1 = parse_mult_expr(p, ts)) {
if (Token const* tok = ts.next()) {
switch (tok->kind()) {
// advance past the operator and move to parse the 'rest' of the expr
case plus_tok:
case minus_tok:
return parse_add_rest(p, ts, ts.advance(), e1);
default:
return e1;
}
}
// no operator or rhs means end of expr
else
return e1;
}
return nullptr;
}
// add-rest ::= '+' mult_expr (add-rest)
// '-' mult_expr (add-rest)
//
// assuming the first mult_expr has already been parsed
// we start to parse the 'rest' of the expression
Expr*
parse_add_rest(Parser& p, Token_stream& ts, Token const* tok, Expr* e1)
{
if (Expr* e2 = parse_mult_expr(p, ts)) {
if (Token const* t = ts.next()) {
// keep parsing the 'rest' while we still have a valid operator
if (is_additive_op(t->kind()))
return parse_add_rest(p, ts, ts.advance(), p.on_binary(tok, e1, e2));
else
return p.on_binary(tok, e1, e2);
}
else
return p.on_binary(tok, e1, e2);
}
error("Expected expression after additive expr: ");
print(e1);
print(tok);
print("\n");
return nullptr;
}
