Inferred latches

[dxur]

Clash do not prevent creating latches in combinational circuits by using infinite recursion

latch clk d = q
  where
    q = if clk then d else q

[christiaanb]

Correct, there is currently no static analysis that determines you have specified what is basically a level-sensitive sequential element.

That being said, you cannot run the circuit as a regular Haskell program either. Trying to do so would either result in a "blinking cursor" on the command-line, or the program throwing a <<loop>> exception. So in that sense, it is observable whether you created a latch, by "simply" simulating, in Haskell, the circuit that you specified.

Currently, when simulating, you would probably just see the <<loop>> exception, but would have no idea where in your circuit description it comes from; which is highly unsatisfactory. That being said, we have asked some of the GHC Haskell compiler maintainers to help us improve this situation in the coming quarter.