> > x := -3 // does NOT mean get the value 3, negate that, and assign to the > location known as x.
Correction: Number literals in go don't include a sign in their definition: https://golang.org/ref/spec#Integer_literals So, yes, it does mean exactly that :) Your explanation, however, does make some kind of sense. Enough, in any case, to not spend any more energy on the question :) On Sat, Aug 20, 2016 at 1:00 AM, Michael Jones <michael.jo...@gmail.com> wrote: > My answer is philosophical, and possibly not what is wanted, but it is > informed. Here goes: > > > > Backstory: Unary Minus, as taught in computer science and implemented in > languages and instruction sets and so forth is slightly confusing and often > confusingly described. > > > > x := -y // means get the value of y, negate that, and assign to the > location known as x. > > > > This is what we commonly think of when seeing unary minus. It is proper. > However this… > > > > x := -3 // does NOT mean get the value 3, negate that, and assign to the > location known as x. > > > > …instead it means “assign the value ⁻3 to x”, where negative 3 is a single > idea, not two as in (Negate 3). The raised minus sign is from Kenneth > Iverson, who used it in APL to make the point that the ‘⁻’ and ‘-‘ have > entirely different meanings. > > > > There is a Wikipedia article about this but its scholarship is, well, more > about usage than history. They talk about the raised minus as an elementary > school teaching tool (which it may be) but they leave it there with little > suggestion of its illustrious past. Yet, to their credit there is a handy > example: > > > > ⁺3 − ⁻5 becomes ⁺3 + ⁺5 = ⁺8 > > > > where you might imagine a teacher saying “positive three minus negative > five becomes…” which is nice. (A sophisticated college CS teacher or parser > coder might instead say “plus 3 minus minus 5 becomes…” ;-) We don’t have > the raised minus to say “here is a negative number” so we make use of the > unary rather than binary minus to suggest negative. You use what you have. > > > > Now, on to the original question: > > > > Standard floating point output since the 1950’s has allowed printing of > either blank or “+” as the prefix for positive floating point values and, > necessarily, the lowered minus “-“ for negative values; we get the ‘+’ with > a printf format like “%+10.4f”. > > > > It is handy to be able to parse what is output, such as numerical > approximations and weights in formula source code, so the parsing of > “3.1415” was made to accept “+3.1415” for the same meaning, and of course > “-3.1415” since we lack the raised minus. > > > > Since floating point values accept the stylistic ‘+’ prefix, so do integer > values. > > > > ..and here we are today, some 50 years later. > > > > P.S. If you visited Thomas Payne’s bookshop in London (in the 1750s) you > could have bought your own copy of Francis Maseres’ *“A dissertation on > the use of the negative sign in algebra: containing a demonstration of the > rules usually given concerning it; and shewing how quadratic and cubic > equations may be explained, without the consideration of negative roots. To > which is added, as an appendix, Mr. Machin's quadrature of the circle.”* > You could have enjoyed much discussion of the new style of writing and its > advantages. > > > > > > *From: *"'Thomas Bushnell, BSG' via golang-nuts" < > golang-nuts@googlegroups.com> > *Reply-To: *"Thomas Bushnell, BSG" <tbushn...@google.com> > *Date: *Friday, August 19, 2016 at 1:36 PM > *To: *Axel Wagner <axel.wagner...@googlemail.com>, Rob Thornton < > rthornton...@gmail.com> > *Cc: *golang-nuts <golang-nuts@googlegroups.com> > *Subject: *Re: [go-nuts] Unary + > > > > In C, the type is promoted. But this ain't C. No clue what the point is in > Go. It would function as a compile-time type-check for "numeric" I guess, > but what would be the point? > > > > > > On Fri, Aug 19, 2016 at 1:32 PM 'Axel Wagner' via golang-nuts < > golang-nuts@googlegroups.com> wrote: > > x would already be signed during implicit type inference. The inferred > type is either the one specified in an argument or declaration, or it's the > default type (which is int, thus signed). > > > > I don't know the answer to your question though. I didn't even know this > existed… > > > > On Fri, Aug 19, 2016 at 9:54 PM, Rob Thornton <rthornton...@gmail.com> > wrote: > > What is the purpose of the unary '+' operator? In both C and Go they are > syntactically correct but neither generate instructions to modify the > expression. > > The '-' operator obviously generates a neg or sub from 0 instruction to > negate the result by inverting the expression with an add with carry. > > I know of no single instruction or pair of instructions to reliably ensure > any value or expression is always positive so why include this unary > operator at all? Is there a purpose I'm missing? Or is it just for clarity > or force an implicit variable to be signed? > > As in: > > x := +5 > > Would this ensure that x must be signed during impicit type inference? > > If I read the specification correctly, this would also affect the > resolution of untyped constants. Is this correct? > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > > > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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