firstset.go

// Returns the first-set for the given non-terminal.
func firstSet (b byte, g I) ([]byte, error) {
    var set []byte = []byte{};
    var hasEpsilon bool = false;

    // Ensure b is a non-terminal.
    if !isNT(b) {
        return nil, errors.New("First-Set only valid for non-terminals!");
    }

    // Determine if epsilon is included in the grammar.
    for p := range g {

        // Skip irrelevant productions.
        if (p.lhs != b) continue;

        // Check if the production leads to an empty rule (epsilon).
        if (len(p.rhs) == 0) {
            hasEpsilon = true;
            set = append(set, '@');
            break;
        }
    }

    // Parse through all self-rules.
    for p := range g {

        // Skip irrelevant productions.
        if (p.lhs != b) continue;

        // If production is a terminal, add it to first-set.
        if (len(p.rhs) == 1 && isNT(p.rhs[0])) {
            set = append(set, p.rhs[0]);
            continue;
        }
    }

    // If epsilon is in production, check the other rules.
    if (hasEpsilon == false) {
        return set, nil;
    }

    // Otherwise check the other rules. 
    
}