[racket] Strange contracts in the tutorial

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Mon Jun 13 19:55:54 EDT 2011

The author tried to say it doesn't return. 

In a Racket-like context, the author could have specified 

 ;; render-blog-page : request -> ∅

Since there are no elements in the emptyset, this specification says the same thing mathematically, using Racket's `types as sets' standard form of loose reasoning. I doubt it would have been more easily understood. 

An MLer could have said α again because it is impossible to return something of this type if the function's domain isn't specified as such. Would this help? 

-- Matthias

On Jun 13, 2011, at 5:13 PM, Rodolfo Carvalho wrote:

> Hi,
> I'm reading the User Guide: Continue and I'm puzzled with some contracts that reads:
> ; render-blog-page: request -> doesn't
> ; Produces an doesn't page of the content of the
> ; BLOG.
> Is it correct? What does it mean that it "produces an doesn't"?
> []'s
> Rodolfo Carvalho
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