[plt-scheme] typed scheme vs. PLAI types

From: keydana at gmx.de (keydana at gmx.de)
Date: Tue Feb 16 05:09:06 EST 2010

> you don't add the tags to turn Relation into RelExpr. This work:
> (eval-relexpr (make-Union (make-Rel suppliers_1-3) (make-Rel suppliers_4-5)))
> Note the use of make-Rel.

Ah, of course, I overlooked that... Thanks a lot!

Still, I don't understand in which cases I have to annotate an expression?
Also, when I try annotating (although in the following case it's not necessary it seems, as suppliers_1-3 is constructed as a Relation) like this: 

(ann suppliers_1_3 Relation)

I get the error

. Type Checker: Unbound type name Relation in: Relation

which I don't understand.

Thanks a lot again,

> HTH,
> N.

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