while-loop — minizig

Add while. Save the position before the condition. Loop: re-parse the condition from the saved position each time, execute or skip the body.

    testCase(
        \\var s: i64 = 0; var i: i64 = 1;
        \\while (i < 6) {
        \\    s = s + i;
        \\    i = i + 1;
        \\}
        \\s
    , 15, &varNames, &varValues, &varCount);

Add to executeStatement's keyword chain, next to if:

        if (stringsEqual(firstWord, "while")) {
            const loopPos = pos.*;
            var last: i64 = 0;
            while (true) {
                pos.* = loopPos;
                if (source[pos.*] == '(') {
                    pos.* += 1;
                    skipSpaces(source, pos);
                }
                const cond = parseExpression(source, pos, names, values, count);
                if (source[pos.*] == ')') {
                    pos.* += 1;
                    skipSpaces(source, pos);
                }
                if (cond == 0) {
                    skipBlock(source, pos);
                    break;
                }
                last = executeBlock(source, pos, names, values, count);
            }
            return last;
        }

Notice something weird: we're re-parsing the condition string from scratch every iteration. We jump pos.* back to loopPos, re-read the characters, re-evaluate the expression. It works, but it means we're paying the parsing cost every loop iteration. This is one reason we'll eventually want a tree -- you parse once, walk the tree as many times as you like.