Re: Expression-local variables and 'let'

>>You can call the body multiple times. 'foreach' is implemented in 
>>nice.lang, for instance.
>>Am I missing something?
>>    
>>
>
>Yes, you can execute the body multiple times but you can only execute the
>condition once. The type of a 'while' function would be:
>     (() -> bool, () -> ()) -> ()
>
>But, the calling syntax only works for a function of type:
>     (bool, () -> ()) -> ().
>  
>
You're right.

One way to handle this would be to allow a declaration like:
  void while(delayed<boolean> condition, delayed<void> body) { ... }

delayed<T> would be basically ()->T, but with the additional rule that 
an expression of type T can be used where delayed<T> is expected 
(semantically, it is wrapped inside a closure at that point, and so it's 
value is not evaluated). It's probably needed to introduce those delayed 
types because I would think it's unwise to silently convert from T to 
()->T everywhere.

I first thought about using the name lazy<T>, but that's actually a 
different concept (once the value is computed, you "cache" it, not 
recompute it at each use).

Daniel



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