<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=iso-8859-1"> <META content="MSHTML 6.00.6000.16587" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY style="WORD-WRAP: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space" bgColor=#ffffff> <DIV><FONT face=Arial size=2>(case (-> ..) (-> ..)) works perfect. Why did I miss that? It is in the docs, although at the very end of the chapter.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>I did already go along the line of your example with ->*, but it is less restrictive than I want.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Thanks,</FONT></DIV> <DIV><FONT face=Arial size=2>Jos</FONT></DIV> <BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B> <A title=d.j.gurnell@gmail.com href="mailto:d.j.gurnell@gmail.com">Dave Gurnell</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A title=plt-scheme@list.cs.brown.edu href="mailto:plt-scheme@list.cs.brown.edu">plt-scheme@list.cs.brown.edu</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, February 06, 2008 2:04 PM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [plt-scheme] contract question</DIV> <DIV><BR></DIV>I'm not sure why you can't use or/c (see below), but you should be able to use ->* or case->: <DIV><BR class=webkit-block-placeholder></DIV> <DIV> <DIV><SPAN class=Apple-style-span style="COLOR: rgb(0,0,0)"> <DIV><FONT size=+0><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px">    (define (example a (b #f))<BR>      (if b (+ a b) (void)))</SPAN></FONT></FONT></DIV> <DIV><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px"><BR class=webkit-block-placeholder></SPAN></FONT></DIV>->* specifies contracts for variable arity procedures:<BR> <DIV><BR class=webkit-block-placeholder></DIV> <DIV><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px">    (provide/contract</SPAN></FONT></DIV> <DIV><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px">     (example (->* (number?) (number?) (or/c number? void?))))</SPAN></FONT></DIV></SPAN> <DIV><BR class=webkit-block-placeholder></DIV>case-> is intended for contracts on case-lambdas, but it should work okay here:</DIV> <DIV><BR></DIV> <DIV> <DIV><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px">    (provide/contract</SPAN></FONT></DIV> <DIV><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px">     (example (case-> (-> number? number? number?)</SPAN></FONT></DIV> <DIV><FONT class=Apple-style-span face=Monaco size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px">                      (-> number? void?))))</SPAN></FONT></DIV> <DIV><BR></DIV> <DIV>I thought or/c could only be used on value contracts but the documentation suggests otherwise.</DIV> <DIV><BR class=webkit-block-placeholder></DIV></DIV> <DIV> <DIV> <DIV> <DIV> <DIV> <DIV>Cheers,</DIV> <DIV><BR class=webkit-block-placeholder></DIV> <DIV>-- Dave</DIV> <DIV><BR></DIV> <BLOCKQUOTE type="cite"><SPAN class=Apple-style-span style="WORD-SPACING: 0px; FONT: 13px 'Lucida Grande'; TEXT-TRANSFORM: none; COLOR: rgb(0,0,0); TEXT-INDENT: 0px; WHITE-SPACE: normal; LETTER-SPACING: normal; BORDER-COLLAPSE: separate; orphans: 2; widows: 2; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0"> <DIV bgcolor="#ffffff"> <DIV><FONT face=Arial size=2>Finally I decided to try contracts. I tried:</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>#| require one or two numbers<BR>   promise to return a number if two numbers are given<BR>   promise void if one number is given |#</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>#lang scheme</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>(provide/contract<BR> (example<BR>  (or/c<BR>   (-> number? number? number?)<BR>   (-> number? void?))))</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>(define (example a (b #f))<BR> (if b (+ a b) (void)))</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>This compiles, but it wont run:</FONT></DIV> <DIV> </DIV> <DIV><FONT face=Arial size=2>Welcome to DrScheme, version 3.99.0.10-svn4feb2008 [3m].<BR>Language: Module custom.<BR>or/c: two arguments, (-> number? void?) and (-> number? number? number?), might both match #<procedure:example></FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Why? What is wrong in my contract? May be I am wanting an impossible contract?</FONT></DIV> <DIV><FONT face=Arial size=2>or/c repeats exactly what I want, but does not accept it.</FONT></DIV> <DIV><FONT face=Arial size=2>I think I am missing something fundamental, but I can't find an answer in the docs.</FONT></DIV> <DIV><FONT face=Arial size=2>Thanks,<SPAN class=Apple-converted-space> </SPAN></FONT><FONT face=Arial size=2>Jos Koot</FONT></DIV>_________________________________________________<BR> For list-related administrative tasks:<BR> <A href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</A><BR></DIV></SPAN></BLOCKQUOTE></DIV><BR></DIV></DIV></DIV></DIV></DIV> <P> <HR> <P></P>_________________________________________________<BR>  For list-related administrative tasks:<BR>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme<BR></BLOCKQUOTE></BODY></HTML>