When a conditional expression is static, where can it be used?
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From: Georg Bauhaus on 30 Jun 2010 06:39 A totally meaningless example just to illustrate the question: What is it that a compiler must report for the case statement below, if anything? procedure CE is type DOW is (Mo, Tu, We, Th, Fr, Sa, So); procedure P is begin null; end P; D: constant DOW := We; begin case D is when Mo | We | Fr => P; when (if D = We or D = Fr then So else Sa) => P; when Tu | Th => P; end case; end CE; Georg
From: Pascal Obry on 30 Jun 2010 07:25 Le 30/06/2010 12:39, Georg Bauhaus a �crit : > procedure CE is > > type DOW is (Mo, Tu, We, Th, Fr, Sa, So); > > procedure P is begin null; end P; > > D: constant DOW := We; > begin > case D is > when Mo | We | Fr => P; > when (if D = We or D = Fr then So else Sa) => P; > when Tu | Th => P; > end case; > end CE; This should not compile I would say. Pascal. -- --|------------------------------------------------------ --| Pascal Obry Team-Ada Member --| 45, rue Gabriel Peri - 78114 Magny Les Hameaux FRANCE --|------------------------------------------------------ --| http://www.obry.net - http://v2p.fr.eu.org --| "The best way to travel is by means of imagination" --| --| gpg --keyserver keys.gnupg.net --recv-key F949BD3B
From: Adam Beneschan on 30 Jun 2010 10:39 On Jun 30, 3:39 am, Georg Bauhaus <rm.dash-bauh...(a)futureapps.de> wrote: > A totally meaningless example just to illustrate > the question: What is it that a compiler must report > for the case statement below, if anything? The choice "Sa" is not covered by any alternative. Other than that, I don't think there's anything wrong with the CASE statement, and if you had included a "when others =>" alternative I think it would be legal. I'm not sure what potential problem you were trying to illustrate. -- Adam > > procedure CE is > > type DOW is (Mo, Tu, We, Th, Fr, Sa, So); > > procedure P is begin null; end P; > > D: constant DOW := We; > begin > case D is > when Mo | We | Fr => P; > when (if D = We or D = Fr then So else Sa) => P; > when Tu | Th => P; > end case; > end CE; > > Georg
From: Dmitry A. Kazakov on 30 Jun 2010 13:35 On Wed, 30 Jun 2010 07:39:24 -0700 (PDT), Adam Beneschan wrote: > On Jun 30, 3:39�am, Georg Bauhaus <rm.dash-bauh...(a)futureapps.de> > wrote: >> A totally meaningless example just to illustrate >> the question: �What is it that a compiler must report >> for the case statement below, if anything? > > The choice "Sa" is not covered by any alternative. Other than that, I > don't think there's anything wrong with the CASE statement, and if you > had included a "when others =>" alternative I think it would be > legal. I'm not sure what potential problem you were trying to > illustrate. Let me propose this one instead: � �type DOW is (Mo, Tu, We, Th, Fr, Sa, So); � �case D is � � � when (if D = Mo then Tu else Mo) => P; � � � when (if D = Tu then Tu else Mo) => Q; � � � when We..So => R; � �end case; The above is equivalent to: � �case D is � � � when Tu => P; � � � when Mo => Q; � � � when We..So => R; � �end case; But as Pascal suggested, it should not compile because D is not static. As for the problem Georg had in mid. Maybe it is this. Let you have some function, say Gamma function. Now, x : constant := 0.1; Gx : constant := Gamma (1.1); -- Illegal, what a pity Let us open the table of Gamma, scan it, and write something like: (if x < 0.0 then ... elsif x < 0.01 then ... ) This wonderful static function can then copied and pasted everywhere you wanted to evaluate Gamma at compile time. Is it legal? -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de
From: Adam Beneschan on 30 Jun 2010 15:12
On Jun 30, 10:35 am, "Dmitry A. Kazakov" <mail...(a)dmitry-kazakov.de> wrote: > On Wed, 30 Jun 2010 07:39:24 -0700 (PDT), Adam Beneschan wrote: > > On Jun 30, 3:39 am, Georg Bauhaus <rm.dash-bauh...(a)futureapps.de> > > wrote: > >> A totally meaningless example just to illustrate > >> the question: What is it that a compiler must report > >> for the case statement below, if anything? > > > The choice "Sa" is not covered by any alternative. Other than that, I > > don't think there's anything wrong with the CASE statement, and if you > > had included a "when others =>" alternative I think it would be > > legal. I'm not sure what potential problem you were trying to > > illustrate. > > Let me propose this one instead: > > type DOW is (Mo, Tu, We, Th, Fr, Sa, So); > > case D is > when (if D = Mo then Tu else Mo) => P; > when (if D = Tu then Tu else Mo) => Q; > when We..So => R; > end case; > > The above is equivalent to: > > case D is > when Tu => P; > when Mo => Q; > when We..So => R; > end case; > > But as Pascal suggested, it should not compile because D is not static. Ummm, not quite, because (1) Pascal didn't say anything about *why* he thought it shouldn't compile (his entire statement was "This should not compile I would say"), and (2) in the OP's original example, D *is* static. In your example, you're right that it shouldn't compile because D is not static, but that's a different issue. (Well, I *assume* D isn't static. Since your example doesn't include a declaration of D, I can't tell.) > As for the problem Georg had in mid. Maybe it is this. Let you have some > function, say Gamma function. Now, > > x : constant := 0.1; > Gx : constant := Gamma (1.1); -- Illegal, what a pity > > Let us open the table of Gamma, scan it, and write something like: > > (if x < 0.0 then ... elsif x < 0.01 then ... ) > > This wonderful static function can then copied and pasted everywhere you > wanted to evaluate Gamma at compile time. Is it legal? Gamma cannot be a static function (4.9(18-22)). You cannot write a static function (other than an enumeration literal, which is technically a static function). -- Adam |