using selfhost.vm.scan as MiniVmScan

static box MiniVmCompare {
  // Compare(lhs int, rhs int) minimal: prints 0/1 and returns next pos or -1
  try_print_compare_at(json, end, print_pos) {
    local scan = new MiniVmScan()
    local k_cp = "\"kind\":\"Compare\""
    local cpos = scan.index_of_from(json, k_cp, print_pos)
    if cpos <= 0 || cpos >= end { return -1 }
    local k_op = "\"operation\":\""
    local opos = scan.index_of_from(json, k_op, cpos)
    if opos <= 0 || opos >= end { return -1 }
    local oi = opos + k_op.length()
    local oj = scan.index_of_from(json, "\"", oi)
    if oj <= 0 || oj > end { return -1 }
    local op = json.substring(oi, oj)
    // lhs value
    local k_lhs = "\"lhs\":{\"kind\":\"Literal\""
    local hl = scan.index_of_from(json, k_lhs, oj)
    if hl <= 0 || hl >= end { return -1 }
    local k_v = "\"value\":"
    local hv = scan.index_of_from(json, k_v, hl)
    if hv <= 0 || hv >= end { return -1 }
    local a = scan.read_digits(json, hv + k_v.length())
    // rhs value
    local k_rhs = "\"rhs\":{\"kind\":\"Literal\""
    local hr = scan.index_of_from(json, k_rhs, hl)
    if hr <= 0 || hr >= end { return -1 }
    local rv = scan.index_of_from(json, k_v, hr)
    if rv <= 0 || rv >= end { return -1 }
    local b = scan.read_digits(json, rv + k_v.length())
    if !a || !b { return -1 }
    local ai = scan._str_to_int(a)
    local bi = scan._str_to_int(b)
    local res = 0
    if op == "<"  { if ai <  bi { res = 1 } }
    if op == "==" { if ai == bi { res = 1 } }
    if op == "<=" { if ai <= bi { res = 1 } }
    if op == ">"  { if ai >  bi { res = 1 } }
    if op == ">=" { if ai >= bi { res = 1 } }
    if op == "!=" { if ai != bi { res = 1 } }
    print(res)
    // advance after rhs object (coarsely)
    return rv + 1
  }
}