OpenEuphoria

RE: Type Class!

• Posted by tacitus <indorlaw at zdnetonebox.com> Mar 17, 2001
• 509 views

i was interested in types as well - but soon came to the conclusion that 
they are really just functions disguised in a slightly different syntax. 
the refman hints at this. mts's post simply confirms my view.

to demonstrate, i was writing a library routine for dos that parsed an 
html file into a file readable by dos.  i defined a number of tags as 
the type line_break, something like this:-

type line_break(sequence tag)
    if equal(tag, "<br>")
       or equal(tag, "<p>")
       or equal(tag, "<div>") then
    return 1
    else return 0
    end if
end type

(i could have done better by replacing the if statement with:-
return equal(tag, "<br>") or equal(tag, "<p>") or equal(tag, "<div>")
)

i could test whether a tag was a line break with:-

if line_break(tag) then etc

i suddenly realised that the same thing could always be done better with 
a function.

function line_break(sequence tag)
    -- if statement as above
    return 1
    else return 0
end function

then test for line break with:

if line_break(tag) then etc

note the similarity. my example is more like the traditional view of a 
type, but mts's examples demonstrate better the relationship with a 
function.

the only difference i can see between a type and a function is that 
types provide error checking by the interpreter, while with functions 
you define your own error checking (or have none at all). generally, i 
would have thought that your own error checking will be more graceful, 
as the program can run to its conclusion or otherwise on your say-so.

i agree there's nothing to be afraid of with types, but also not much to 
be excited about.

cheers

tacitus



Mike The Spike wrote:
> Here's a little trick I fished up just now...
> 
> You like VB huh?
> You like it when you can create a property, and set
> and get the status of a variable...
> Confused?
> No problem, Eu can do that too!
> 
> Here it is...
> If you didn't know you could do this (people are
> afraid of using 'type' nowadays), you'll think how you
> could miss this cool feature of Eu's.
> 
> Ok...
> What if you'd want a variable, that when assigned a
> value, it autmatically processes that data using your
> own specifc code?
> An example?
> Here ya go.
> 
> type type_writer(sequence s)
>     puts(1,s)
>     return 1
> end type
> 
> 
> Now simply say;
> 
> type_writer echo
> echo = "Hello World!"
> 
> 
> What happens?
> "Hello World!" is printed to the screen.
> Also usefull for doing Memory Dumping.
> Keep track of each value assigned to a variable, by
> writing them to disk.
> 
> Wouldn't it be cool to do 'classes' in Eu, FOR REAL?
> Well, you can!
> Like this;
> 
> type class(sequence func)
>     call_proc(func,func[2])
>     return 1
> end type
> 
> Now you can do this!;
> 
> class myclass
> myclass = {"MyPuts","Hello World!"}
> 
> After this assignement,
> routine 'MyPuts' is called with "Hello World!", thus
> writing this string to the screen (assuming that's
> what MyPuts does).
> 
> 
> That ain't all folks...
> There *LOADS* of things you can do with types...
> Go ahead!
> Try it!
> Classes, properties, debugging, resource tracking,
> ByRef passing (routine_id works on types aswell!!),
> etc...
> There's no limits, just your own imagination.
> 
> So go ahead!
> Types won't bite!
> 
> 
> Mike The Spike
> PS. Don't forget to use 'without type_check' for extra
> speed boosts!
> 
> 
>