On 05/26/2016 02:44 PM, Waldek Hebisch wrote: > oldk1331 wrote: >> >>> I'm not sure if this patch creates unnecessary parenthesis elsewhere. >> >> One change I noticed is "unparse(( t-1 )::INFORM)", it used to be >> "t+-1", after patch it's "t+(-1)", is it a bug that it doesn't return "t-1"? > > That is a tricky question. InputForm (and OutputForm) are supposed > to work for all domains. In abelian semigroup containing symbols > and integers 't + -1' makes sense, but 't-1' is undefined: > we can add integer '-1' to symbol 't', but there is no way to > subtract. In principle all nontrivial transformations should be > done in domains (where we have axioms like associativity, etc.).
I still don't see why 't + -1' makes sense. I would always want this as "t+(-1)". To turn that properly back into "t-1" is impossible without information about types. Interestingly what the tex output formatter does is to simply replace "+-" by "-". See https://github.com/fricas/fricas/blob/master/src/algebra/tex.spad#L224 That looks more like a hack. I don't know whether it makes sense to have "-" as an operator in InputForm/OutputForm so that we would get (- t 1) as a result of ( t-1 )::INFORM. The specification of InputForm is rather vague. ++ Domain of parsed forms which can be passed to the interpreter. ++ This is also the interface between algebra code and facilities ++ in the interpreter. 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 post to this group, send email to fricas-devel@googlegroups.com. Visit this group at https://groups.google.com/group/fricas-devel. For more options, visit https://groups.google.com/d/optout.
