[racket] type assertions in plai-typed?

I don't think there's a good way to write type assertions as the
moment, so let's add one. What syntax do you suggest?

At Mon, 6 Jan 2014 11:53:54 -0800, John Clements wrote:
> I’ve bitten the bullet and announced to my PL class that we’ll be using #lang 
> plai-typed. Right now, I’m trying to figure out if there’s an easy way to do 
> type debugging; in particular, I anticipate wanting to make assertions about 
> the type of expressions that are buried inside of other expressions. Is there a 
> form that allows me to do this? I had imagined that I could do it with ‘let’, 
> but ‘let’ doesn’t take any type annotations.
> 
> Currently, the best I’ve got is an in-line application to an identity function 
> with a type attached.  So, for instance, if I have this function
> 
> (define (id x)
>   x)
> 
> … and I want to ensure that the expression ‘x’ has type number, I can write:
> 
> 
> (define (id x)
>   ((lambda ((z : number)) z) x))
> 
> … but that’s pretty painful. Is there an easier way? (Yes, I could add a type 
> annotation to the declaration of ‘x’ and to the return type of the function, 
> but I’m imagining a larger function where the expression in question is neither 
> an argument to nor the result of the function.)
> 
> Many thanks,
> 
> John
> 
> 
> 
> 
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