Re: are there implementation reasons for not providing a break statement in an imperative language?

On 13 Feb., 16:43, 1Z <pdjpurch...@googlemail.com> wrote:
> On Jan 13, 6:09 pm, noitalmost <noitalm...@cox.net> wrote:
>
> > I've noticed that Wirth has continually rejected the idea of a break
> > statement and I was wonder why. Is this purely philosophical, or are
> > there code optimization reasons? Naive code for a break is trivial to
> > implement.
>
> > Is it easier to optimize loops with no break? That is, is the cost of
> > having extra booleans to control the loop less than the cost of
> > messing up the basic blocks with break?
> > [It's a little easy to optimize single-exit loops, but my impression is
> > that the motivation was more like salvation through suffering. -John]
>
> A compromise would be to allow only one "middle exit" per loop, and
> to have it clearly indicated in the syntax rather than looking like
> any old statement.


I defined such a loop with middle exit as example for Seed7.
It could be used like


        loop
            ch := getc(inFile);
        until ch = '\n' do
            stri &:= str(ch);
        end loop;


The meaning of the loop above is the same as


        repeat
            ch := getc(inFile);
            if ch <> '\n' then
                stri &:= str(ch);
            end if;
        until ch = '\n';


Details of the Seed7 loop with middle exit can be found here:
http://seed7.sourceforge.net/manual/syntax.htm#The_syntax_of_a_statement




Greetings Thomas Mertes


--
Seed7 Homepage: http://seed7.sourceforge.net
Seed7 - The extensible programming language: User defined statements
and operators, abstract data types, templates without special
syntax, OO with interfaces and multiple dispatch, statically typed,
interpreted or compiled, portable, runs under linux/unix/windows.

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