type S = (
    [typestate Uninitialized, Connected, Closed]
    int socket [when Connected]
    int bytes_sent [when Connected,Closed]
)

# or

type S = private [typestate Uninitialized, Connected, Closed]

type S = (
    int socket [when Connected]
    int bytes_sent [when Connected,Closed]
)



# more:

func work(int i [!= 0]) return int [!= 0]
{
    int j [< i] = blabla(i)
    cond [j != 4]
    return i - j
}

# since constraint validation is cumbersome, it could be done as follows:
# - statically at compile time, when requested
# - statically at compile time, when there could be UB (how to detect this?)
# - at runtime, when requested at compile time (like clang's sanitizers) - statically at compile time,

# which conditions should be supported? perhaps these:
# - typestates
# - the following for non-var (and non-shared?) values?
#     - enum in / not in / = / !=
#     - elementary type = / !=
#     - integer < > <= >= = !=