Re: Error Trapping
> [ADDITIONAL NITPICKY POINTS: Your "if" statement would result in the
> "true/false condition must be an ATOM" error. It should read "if equal(Obj,
> {})" or "if compare(Obj, {}) = 0" instead. Also, My_Procedure can't return a
> -1, because it's a procedure -- not a function.]
Finally, at least, a correct reply after so many "you should use single qoutes"
..
if v[i] = "" then
.. and ..
if v[i] = '' then
Are both as incorrect as hell.
The problem is the recursive nature of all mathimatical and relational
operators, I suggest Robert wrote a seperate 'mini' -
tutorial on the subject.
Most of all newcomers to Euphoria have problems with this, and explenations such
as:
-- "you should use single qoutes"
-- "you should use equal"
etc.
First of all, both replies assume some algorimic meaning of the program (and
thus take the programming part out of the hands of
the programmer), and lack the explenation *why* ..
The problem isn't in the syntax of the program, its in the understanding of the
programmer. And that will remain a problem until
somebody explains how this works .. somebody asks "why isn't this working" and
half of the people are like "let me do it for
you" .. the list-server community is really great and helpfull to many people,
but it wouldn't hurt any one if we would give it
some thought and what exactly would and would not be helpfull.
This way all our good intentions can have the effect we want it to have.
At the end of this mail is a post I made on the newsgroup on the very same
topic. It should explain this stuff for now (in my
lousy Engish), but I suggest Robert adds a couple of mini-tutorials to the
Euphoria packagae, that explain these kind of things.
Topics I had in mind:
-- Atom VS sequence (In appending, slicing, concationation)
-- Recursive nature of mathimatical & relational operators
-- Simple file I/O
-- How to time a certain routine/technique
-- Windows: a simple how-to do win32 (list of resources, a quick intro to
win32lib or the new Liama)
-- Data management (client/server)
The last topic I will explain a bit futher:
I meant the flow of data. Use local variables to store everything ? Return
all information ? Return a handle.
In other words, a quick how-to setup store information handle-based, etc.
(basic techniques used by almost all libraries managing some kind of data)
Off course, some one else could make such tutorials, but I at least suggest to
pack such tutorials with the standard Euphoria
package.
Now here's the post about the recursive stuff, in my own lacking English..
Michael Dauth <mdauth at bigfoot.com> wrote in message news:7GNTflH8WwB at
mdauth.bigfoot.com...
> Hi,
>
> after banging my head for hours 
I found out that the "="
> operator does not work with sequences, but the equal functions
> does. Am I wrong and if what am I doing if the following code
> does not work:
Indeed, totally correct. If-statements use any legal euphoria express to
represent the TRUE / FALSE value, however Euphoria's
rules about expression (the recursive operator 'theme') allow it in some
occasions to generate a sequence rather than an atom
value.
Sequence is not clearly TRUE or FALSE, therefor the if-statement generates an
error message in such case.
So how do the Euphoria evaluation does work ?
atom a, b, c
a = 1
b = 0
c = not a
? c -- 0
c = a or b
? c -- 1
c = a and b
? c -- 0
sequence d, e, f
d = { 1, 0, 1 }
e = { 0, 1, 1 }
f = not d
? f -- { 0, 1, 0 }
f = d or e
? f -- { 1, 1, 1 }
f = d and e
? f -- { 0, 0, 1 }
object g, h, i
g = 1
h = { 0, 1, 0 }
i = not g
? i -- 0
i = not h
? i -- { 1, 0, 1 }
i = g or h
? i -- { 1, 1, 1 }
i = g and h
? i -- { 0, 1, 0 }
sequence j, k, l
j = { 1, 0, 0 }
k = { 0, 1 }
l = j or k
? l -- { { 1, 1 }, { 0, 1 }, { 0, 1} }
l = j and k
? l -- { { 0, 1 }, { 0, 0 }, { 0, 0 } }
-- What applies to the boolean operators also applies to the mathematical
operators.
-- Example:
object m, n
m = { 1, 2, 3 }
n = m * 2
? n -- { 2, 4, 6 }
n = m * m
? n -- { 1, 4, 9 }
n = m * { 1, 2, 3, 4 }
? n -- { { 1, 2, 3 }, { 2, 4, 6 }, { 3, 6, 9 } }
-- In short terminology:
-- Operators recurse whenever the either one of the two values is an atom or
when the two sequences are of different length.
So, since a string / qouted-sequence is handled just like any other sequence,
the 'equal' _operator_ will recurse the
equal-operation.
You could write a recursive function like this to deal with it:
global function equal (object x, object y)
if atom (x) then
if atom (y) then
return x = y
else
return 0
end if
elsif atom (y) then
return 0
elsif length(x) != length(y) then
return 0
else
for index = 1 to length(x) do
if not equal (x[index], y[index]) then
return 0
end if
end for
return 1
end if
end function
But, guess what ? Its already built-in, and called precisely the same.
You also have compare, but unlike the equal function which will only return an
atom true / false value, compare returns either
zero, minus one and plus one. Example:
atom o, p
o = 1
p = 2
? compare (o, p) --- 1
? compare (p, o) --- -1
? compare (o, o) --- 0
? compare (p, p) --- 1
I hope this was helpful, I always feel examples show more than words alone,
nevertheless, feel free to ask for more explanation
if any part is unclear.
Good luck learning Euphoria ..
Ralf Nieuwenhuijsen
... mailto://nieuwen at xs4all.nl
... mailto://ralf_n at email.com
... http://www.xs4all.nl/~nieuwen
... uin: 9389920
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