chain-interpret — minizig

Now "3+4+5" should give 12. Read the first digit, then loop: skip the +, read the next digit, add it.

Same shape will turn up everywhere.

pub fn main() void {
    const input: [:0]const u8 = "3+4+5";
    var input_pos: usize = 0;

    var result: i64 = @as(i64, input[input_pos]) - '0';
    input_pos += 1;

    // YOU: while input_pos < input.len:
    //        skip the '+', read the next digit, add it to result.

    printString("interpreter result for ");
    printString(input);
    printString(" : ");
    printNumber(result);
    printChar('\n');

    // (the WAT-toggle / VM section from compile-to-wat is still below.
    //  the hand-written WAT and the compiler still only know "3+4",
    //  so the vm result will be wrong until we fix them.)
}

while (input_pos < input.len) {
    input_pos += 1;
    const next_digit: i64 = @as(i64, input[input_pos]) - '0';
    input_pos += 1;
    result = result + next_digit;
}

The input_pos += 1 at the top skips the +. Then we read the next digit and bump past it.

interpreter result for 3+4+5 : 12. The vm result: line will still say 7 until the next two problems catch up.