INim doens not show results of long computations
The first thing I try in a REPL is a slow Fibonacci function, to check that it is not recomputing everything on each new input. So I run

```
nim> proc fib(n: int): int =
....   if n <= 1: n else: fib(n-1) + fib(n-2)
```

and then proceed to ask for

```
nim> fib(6)
8  : int
```

So far, so good. Then I enter

```
nim> fib(40)
```

which just returns the prompt withou giving any result. Every further input takes a few seconds and then it does not give any result.

I am not sure whether `fib(40)` overflows (if I recall correctly, it doesn't) or INim delegates computation to a thread that is killed after a few seconds. In any case, the behaviour of not getting any result back is strange