// Minimal Pattern P5b (Escape Handling) Test Fixture
// Purpose: Verify JoinIR Canonicalizer recognition of escape sequence patterns
//
// Pattern: loop(i < n) with conditional increment on escape character
// Carriers: i (position), out (accumulator)
// Exit: break on quote character
//
// This pattern is common in string parsing:
// - JSON string readers
// - CSV parsers
// - Template engines
// - Escape sequence handlers
//
// Note: VM path uses `print(out)` instead of `ConsoleBox` here because ConsoleBox methods are
// not reliably available in this selfhost fixture; the test focus is JoinIR lowering semantics.

static box Main {
    main() {
        // Test data: string with escape sequence
        // Original: "hello\" world"
        // After parsing: hello" world
        local s = "hello\\\" world"
        local n = s.length()
        local i = 0
        local out = ""

        // Pattern P5b: Escape sequence handling loop
        // - Header: loop(i < n)
        // - Escape check: if ch == "\\" { i = i + 1 }
        // - Process: out = out + ch
        // - Update: i = i + 1
        loop(i < n) {
            local ch = s.substring(i, i + 1)

            // Break on quote (string boundary)
            if ch == "\"" {
                break
            }

            // Handle escape sequence: skip the escape char itself
            if ch == "\\" {
                i = i + 1  // Skip escape character (i increments by +2 total with final i++)
                if i < n {
                    ch = s.substring(i, i + 1)
                }
            }

            // Accumulate processed character
            out = out + ch
            i = i + 1  // Standard increment
        }

        // Expected output: hello" world (escape removed)
        print(out)

        return "OK"
    }
}