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I don't think there is madness here.<br>I believe the half range of CARDINAL helps avoid it.<br>A confusing point in C is comparison that includes conversion<br>is magnitude or sign preserving -- comparing int and unsigned.<br><br>Back to Modula-3:<br><br>a := b;<br>c := a + d;<br><br>vs.<br><br>c := b + d;<br><br><br>are different?<br>Isn't that strange?<br><br><br>Compare with<br>a : = b;<br>c := d[a];<br><br>and<br><br>c := d[b];<br><br>we have decided they are the same, among others.<br><br><br>There's something about "kinda sorta transitive" here.<br>Or, like, "why should I have to move values through temporaries in some<br>cases but not others?"<br><br> - Jay<br><br><br><br><hr id="stopSpelling">Subject: Re: [M3devel] index array by longint?<br>From: hosking@cs.purdue.edu<br>Date: Sat, 9 Jan 2010 23:46:39 -0500<br>CC: rodney_bates@lcwb.coop; m3devel@elegosoft.com<br>To: jay.krell@cornell.edu<br><br>
<base><div>I have a feeling that the mixed arithmetic option is losing favor. It is a slippery slope to C madness.</div><div><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><div style="word-wrap: break-word;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><div><span class="ecxApple-style-span" style="font-size: medium;"><font class="ecxApple-style-span" color="#0000ff" face="'Gill Sans'"><br></font></span></div></span></span></span></span></span></span></span></span></div></span></span></div><div><div>On 9 Jan 2010, at 23:42, Jay K wrote:</div><br class="ecxApple-interchange-newline"><blockquote><span class="ecxApple-style-span" style="border-collapse: separate; font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><div class="ecxhmmessage" style="font-size: 10pt; font-family: Verdana;">There are more cases:<br><br>=, #, <, >, IN, etc. have this same "you can mix<br>if they are assignable" rule.<br><br><a href="http://www.cs.purdue.edu/homes/hosking/m3/reference/relations.html">http://www.cs.purdue.edu/homes/hosking/m3/reference/relations.html</a><br><br> infix =, # (x, y: Any): BOOLEAN<br>The operator = returns TRUE if x and y are equal. The operator # returns TRUE if x and y are not equal. It is a static error if the type of x is not assignable to the type of y or vice versa.<br>...<br><br><br>Other places demand equal types:<br><a href="http://www.cs.purdue.edu/homes/hosking/m3/reference/arithmetic.html">http://www.cs.purdue.edu/homes/hosking/m3/reference/arithmetic.html</a><br><br>inc/dec sound looser:<br><a href="http://www.cs.purdue.edu/homes/hosking/m3/reference/incdec.html">http://www.cs.purdue.edu/homes/hosking/m3/reference/incdec.html</a><br><br><br>I still think mixed operations are reasonable and the result types not so surprising.<br>a := b;<br><br>vs. a := b + c;<br><br>The first is clear even if and b have different types, but the second is not, if b and c have different types?<br>They seem pretty equally clear/unclear to me..<br><br><br> - Jay<br><br><br><hr id="ecxstopSpelling">From:<span class="ecxApple-converted-space"> </span><a href="mailto:hosking@cs.purdue.edu">hosking@cs.purdue.edu</a><br>Date: Sat, 9 Jan 2010 23:22:44 -0500<br>To:<span class="ecxApple-converted-space"> </span><a href="mailto:rodney_bates@lcwb.coop">rodney_bates@lcwb.coop</a><br>CC:<span class="ecxApple-converted-space"> </span><a href="mailto:m3devel@elegosoft.com">m3devel@elegosoft.com</a><br>Subject: Re: [M3devel] index array by longint?<br><br><div><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><div style="word-wrap: break-word;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><span class="ecxecxApple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;"><div><span class="ecxecxApple-style-span" style="font-size: medium;"><font class="ecxecxApple-style-span" color="#0000ff" face="'Gill Sans'">That's very nice! I like it. I think we can use it....</font></span></div></span></span></span></span></span></span></span></span></div></span></span></div><div><br class="ecxecxwebkit-block-placeholder"></div><div>Right now I am tracking bugs in range checking. Some were introduced by my LONGINT changes (sigh!) but others appear to have been around a while before that.</div><div><br></div><div>For example:</div><div><br></div><div>VAR s: CARDINAL := LAST(INTEGER);</div><div>BEGIN INC(s) END;</div><div><br></div><div>did not result in a run-time error. I think I have fixed that now (commit to come).</div><div><br></div><div>But, even worse:</div><div><br></div><div>VAR s: CARDINAL := LAST(INTEGER);</div><div><div>BEGIN WITH x = s DO x := VAL(ORD(x) + 1, CARDINAL) END END;</div><div><br></div><div>also does not give a run-time error.</div><div><br></div><div>The result is that you can store FIRST(INTEGER) in a CARDINAL. Yikes!</div><div><br></div></div><div><div>On 9 Jan 2010, at 21:54, Rodney M. Bates wrote:</div><br class="ecxecxApple-interchange-newline"><blockquote><div>When writing my original proposal, I agonized at length over whether<br>to allow (subranges of) LONGINT to be the index type of an array type. In the<br>end, I decided that gave a poor ratio of practical benefit to language<br>and implementation complexity.<br><br>However, note, from 2.6.3, "Designators,<br><br>"a[i]<br> denotes the (i + 1 - FIRST(a))-th element of the array a. The expression a[i] is a<br> designator if a is, and is writable if a is. The expression i must be assignable<br>--------------------------------------------------------------------------^<br> to the index type of a. The type of a[i] is the element type of a."<br><br>So, by existing rules about assignability, when referring to an element of an<br>array, the subscript expression could have base type LONGINT, and would just<br>be "assigned" in the usual way to the index type, a subrange of INTEGER.<br>This is one of the dozen or so places assignability is used in the language.<br><br><br><br>Jay K wrote:<br><blockquote>Index array by longint?<br></blockquote><blockquote>With runtime check that it is <= LAST(INTEGER)?<br></blockquote><blockquote> Or really, with runtime bounds check against the array size.<br></blockquote><blockquote>Seems reasonable?<br></blockquote><blockquote>Aids the rd/wr change.<br></blockquote><blockquote>A little bit of pain to implement..unless INTEGER and LONGINT have a common base...<br></blockquote><blockquote> - Jay<br></blockquote></div></blockquote></div><br></div></span><br class="ecxApple-interchange-newline"></blockquote></div><br> </body>
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