In terms of defining any kind of variable, the language and its associated semantics should have a [bottom] value. Interestingly, FriCAS does have such a value defined. However, what is not clear is whether this [bottom] can serve for all domains.
There are a couple of alternatives here. One is that every domain has its own [bottom] value seperate from all other domains. Another is that all domains inherit the same [bottom] value. I am in the process of looking at the FriCAS language to see where the semantic definition is either problematic or not defined. There appears to be quite a number of such things to fix. Reading the various threads shows that some serious language definitions are required. Regards to all of you On Tue, 7 Nov 2023, 11:28 pm Ralf Hemmecke, <r...@hemmecke.org> wrote: > On 11/7/23 02:29, Waldek Hebisch wrote: > >> Yes, exactly that is the point. qnew claims to return an object of type > %, > >> but, in fact, it doesn't. > > > > Well, result of 'qnew' is uninitialized, but this does not differ > > much from (note no initialization) > > > > a : T > > Maybe technically (i.e. how it is implemented in the compiler) it gives > similar things, but conceptually, I would say that "a:T" is different. > It is a declaration and thus just a hint to the compiler/interpreter > that when this identifier is used it is to be considered as something of > type T. However, I would expect the compiler to yell at me when I write > code like > > ======================= > )abbrev package FOO Foo > Foo: E == I where > E ==> with > foo: () -> Integer > I ==> add > foo(): Integer == > a: Integer > b: Integer := a > ======================= > > Unfortunately, it doesn't. :-( > > > Would you say that a does not have type T? > > It has type T, but after a declaration a:T, there is not yet reservation > of memory on my computer, so in fact, I do not yet have a variable, just > a hint to the compiler that the identifier "a" has type T when it comes > to type checking. > > >>> We could add the followowing to description of 'qnew': > >>> > >>> Use only when you know what you are doing. > >> > >> That is one thing, but does not give enough information. How should a > user > >> know what he is doing? Where would he get this information from? > > > > One of fundamental commandments of programming is: > > > > "Thou shall not attempt to read uninitialized variables" > > Of course. But putting a big warning sign is much better than just > mystically saying "Use only when you know what you are doing." and not > telling where to get information about it. It is like saying "Do not use > this function, because we are not telling you what it does." > > I do not quite get your rejection of more informative documentation. > Put whatever you want into the ++ docstring. > I just wanted to say that I am more on the side of having documentation > that does not require uses to look at the code in order to understand > what a function does. > > > This is general programming knowledge, to get such knowledge > > Dijkstra "Discipline of programming" may be good start. > > Are you saying that people how haven't read this, should not use FriCAS? > I fear that then many mathematicians are excluded from or shy away from > FriCAS. > > > But there is more to this: people may think that someting like > > > > a := qnew(4, 4)$Matrix(Float) > > b := a(1,1) - a(1, 1) > > Why? a(1,1) is clearly the same as elt(a,1,1), i.e. use of a in a > function. Forbidden by my ++ suggestion. > > > Do you want to add a warning in FriCAS book in section describing > > declarations that one should initialize variables before use? > > Yes, why not. We all know that there is a difference between a FriCAS > (programming) variable and a variable (i.e. something that evaluates to > itself). In traditional CAS that's not totally easy to understand for a > first time user. > > Ralf > > -- > You received this message because you are subscribed to the Google Groups > "FriCAS - computer algebra system" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to fricas-devel+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/fricas-devel/1afe4a05-d804-42ca-802f-6f813f6501eb%40hemmecke.org > . > -- You received this message because you are subscribed to the Google Groups "FriCAS - computer algebra system" group. To unsubscribe from this group and stop receiving emails from it, send an email to fricas-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/fricas-devel/CAEnaMTFcE4k5BsCx-%2BhDsV4%3DsoF2u%3Dhx4ckV1vaGdZvXpNZXPQ%40mail.gmail.com.
