<HTML><BODY>I know, what is the problem.  (Listof (Listof String)) is too wide. It allows '(() ("a" "b")), that is inusable for assoc. So you should promise your sublists not to be empty. (define: mystringlistlist : (Listof (Pairof String (Listof String))) (list (list "a" "b") (list "c" "d"))) (assoc "a" mystringlistlist) => '("a" "b") Понедельник, 24 июня 2013, 8:40 UTC от "Tim K." <tk@crono.co.uk>: <BLOCKQUOTE class=mailru-blockquote style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 10px; MARGIN: 10px; BORDER-LEFT: #0857a6 1px solid; PADDING-RIGHT: 0px"> <DIV> <DIV class="js-helper js-readmsg-msg"> <STYLE type=text/css></STYLE> <DIV class=mr_read__body id=style_13720754850000001016><BASE href="https://e.mail.ru/" target=_self> <DIV id=style_13720754850000001016_BODY>Sam Tobin-Hochstadt <samth@...> writes: > Can you say more about the problem here? The type of `assoc` mentions > pairs, but you should be able to use it with lists, since they're made > of pairs. Yeah, that's what I had expected as well. This code produces type errors (in 5.3.3, too):     ;; Definitions     (define: mystringlistlist : (Listof (Listof String)) (list (list "a" "b") (list "c" "d")))     (define: mystringpairlist : (Listof (Pairof String String)) (list (cons "a" "b") (cons "c" "d")))     ; Works!     (assoc "a" mystringpairlist)     => '("a" . "b")     ; Type error     (assoc "a" mystringlistlist)     Type Checker: Polymorphic function assoc could not be applied to arguments:     Argument 1:       Expected: a       Given: String     Argument 2:       Expected: (Listof (Pairof a b))       Given: (Listof (Listof String))      in: (assoc "a" mystringlistlist) I thought that Racket maybe didn't accept "a" as a String, so I defined it as one and called assoc with that, but the error is exactly the same. > Here's a version that type checks: <A href="https://gist.github.com/samth/5847063" target=_blank>https://gist.github.com/samth/5847063</A> > > The key is giving a type annotation to `fname` using the #{} syntax. > Typed Racket can figure out how to typecheck the expansion only if you > give it that hint. And the #{} syntax is for adding such hints with > macros like `command-line` that didn't anticipate Typed Racket. Ah, that works, thank you :) Did I not see that in the documentation or is this feature "experimental"? Best Regards, Tim ____________________   Racket Users list:   <A href="http://lists.racket-lang.org/users" target=_blank>http://lists.racket-lang.org/users</A> </DIV><BASE href="https://e.mail.ru/" target=_self></DIV></DIV></DIV></BLOCKQUOTE> -- Roman Klochkov </BODY></HTML>