Re: ABS
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Lewis posted his offering for the ABS function:
> function abs(object x)
> return sqrt(x*x)
> end function
I've avoided this discussion up to this point, but I couldn't resist the
bait. Getting a function as fast as possible is fine, but you probably want
to avoid this approach:
- It can overflow for large numbers
- It's non-intuitive
Naturally, I have my own submission:
function abs( atom a )
if a < 0 then
return -a
else
return a
end if
end function
function apply( object func, object o )
-- recursively apply function to list
-- convert name to identifier
if sequence(func) then
func = routine_id( sequence )
end if
-- atom yet?
if atom( o ) then
o = call_func( func, {o} )
elsif length( o ) > 0 then
for i = 1 to length( o ) do
o[i] = apply( func, o[i] )
end for
end if
return o
end function
So you can "simply" write:
? apply( "abs", {-1,0,1} )
Oh, yeah - because of the limitations of routine_id:
- You have to define apply() AFTER abs()
- You can't use apply() with native functions
And, of course, the code is a real speed demon!
Heh. 
-- David Cuny
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<P><FONT SIZE=3D2>Lewis posted his offering for the ABS =
function:</FONT>
</P>
<P><FONT SIZE=3D2>> function abs(object x)</FONT>
<BR><FONT SIZE=3D2>> return =
sqrt(x*x)</FONT>
<BR><FONT SIZE=3D2>> end function</FONT>
</P>
<P><FONT SIZE=3D2>I've avoided this discussion up to this point, but I =
couldn't resist the bait. Getting a function as fast as possible is =
fine, but you probably want to avoid this approach:</FONT></P>
<P> <FONT SIZE=3D2>- It can =
overflow for large numbers</FONT>
<BR> <FONT SIZE=3D2>- It's =
non-intuitive</FONT>
</P>
<P><FONT SIZE=3D2>Naturally, I have my own submission:</FONT>
</P>
<P> <FONT SIZE=3D2>function =
abs( atom a ) =
</FONT></P>
<P> =
<FONT SIZE=3D2>if a < 0 then</FONT>
<BR> =
<FONT SIZE=3D2>return =
-a</FONT>
<BR> =
<FONT SIZE=3D2>else</FONT>
<BR> =
<FONT SIZE=3D2>return =
a</FONT>
<BR> =
<FONT SIZE=3D2>end if</FONT>
<BR> <FONT SIZE=3D2>end =
function</FONT>
</P>
<P> <FONT SIZE=3D2>function =
apply( object func, object o )</FONT>
<BR> =
<FONT SIZE=3D2>-- recursively apply =
function to list</FONT>
</P>
<P> =
<FONT SIZE=3D2>-- convert name to =
identifier</FONT>
<BR> =
<FONT SIZE=3D2>if sequence(func) =
then</FONT>
<BR> =
<FONT SIZE=3D2>func =
=3D routine_id( sequence )</FONT>
<BR> =
<FONT SIZE=3D2>end if</FONT>
</P>
<P> =
<FONT SIZE=3D2>-- atom yet?</FONT>
<BR> =
<FONT SIZE=3D2>if atom( o ) then</FONT>
<BR> =
<FONT SIZE=3D2>o =3D =
call_func( func, {o} )</FONT>
<BR> =
<FONT SIZE=3D2>elsif length( o ) > 0 =
then</FONT>
<BR> =
<FONT SIZE=3D2>for i =
=3D 1 to length( o ) do</FONT>
<BR> =
<FONT =
SIZE=3D2>o[i] =3D apply( func, o[i] )</FONT>
<BR> =
<FONT SIZE=3D2>end =
for</FONT>
<BR> =
<FONT SIZE=3D2>end if</FONT>
<BR> =
<FONT SIZE=3D2>return o</FONT>
<BR> <FONT SIZE=3D2>end =
function</FONT>
</P>
<BR>
<P><FONT SIZE=3D2>So you can "simply" write:</FONT>
</P>
<P> <FONT SIZE=3D2>? apply( =
"abs", {-1,0,1} )</FONT>
</P>
<P><FONT SIZE=3D2>Oh, yeah - because of the limitations of =
routine_id:</FONT>
</P>
<P> <FONT SIZE=3D2>- You have =
to define apply() AFTER abs()</FONT>
<BR> <FONT SIZE=3D2>- You =
can't use apply() with native functions</FONT>
</P>
<P><FONT SIZE=3D2>And, of course, the code is a real speed =
demon!</FONT>
</P>
<P><FONT SIZE=3D2>Heh. </FONT>
</P>
<BR>
<P><FONT SIZE=3D2>-- David Cuny</FONT>
</P>
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