Sigh, thought everyone (eventually) agreed that we'd change to algol/ada x:=if a>b then 1 else 2; so why are we going on & on & on about this?
john On 2 February 2016 at 13:20, Sven Barth <pascaldra...@googlemail.com> wrote: > Am 02.02.2016 11:42 schrieb "Mark Morgan Lloyd" < > markmll.fpc-pas...@telemetry.co.uk>: > > > > Michael Van Canneyt wrote: > > > >> Call me old fashioned, but then I think > >> foo:=iif(Condition1, > >> iif(Condition2, ThenExpr1, ElseExpr1), > >> iif(Condition3, ThenExpr2, ElseExpr2)); > >> is more clear. > >> > >> The "if then" construct is really confusing. > >> "if then" is a statement, not an expression. > > > > > > Yes, and that's why to get the desired semantics it's more appropriate > to use if then else rather than iif() etc. > > > > Please correct me if I'm wrong, but my understanding is that in all > cases where parameters are passed to a procedure or function they are > evaluated and placed on the stack before the code is called. However the > if then else statement never, under any circumstances, executes code in > the untaken statement/block, and it is that which is the required behaviour > for an "inline if" expression. > > > > If we want to organise it so that FPC can only evaluate function > parameters when required, then it is necessary to implement ALGOL-60's > "call by name" semantics, which were universally agreed to be deeply messy > and perhaps not even what the standard authors intended. > > Compiler intrinsics are not necessarily subject to these rules. Take for > example Assert: the string parameter whig can contain function calls is > only evaluated if assertions are active at all and the condition is false. > Same with the IfThen-intrinsic I had added, it only evalutes the branch > that is taken. > Please note that intrinsics are the exception, not the rule. > > Regards, > Sven > > _______________________________________________ > fpc-pascal maillist - fpc-pascal@lists.freepascal.org > http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal >
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