[REBOL] Rolling your own ideal looper: does Repeat still have a bug?
From: galtbarber:mailandnews at: 25-Aug-2000 19:31
This is the preamble of a multipart MIME formatted message.
If you are reading this text your mail system is most likely
not capable of properly decoding MIME messages. To extract
the contents of this message, save it to a file and then use
an external MIME decoding utility.
--mime-boundary-interchange-39b0bccd
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
Hi.
See attached rebol file and output.
Seems promising, although it turned up
a bug in 'repeat apparently.
I thought that bug had been squashed
a while ago!
Probably this would be interesting
for Elan, Sterling, Brett, Ladislav, etc.
I included the script in this mail, and as an attachment, too.
At first I tried using bind, but I couldn't figure
out how to get what I wanted with that.
So I was pretty lucky I thought to make it work
with word replacement, even dealing with "scoping"
properly, so far as my testing indicates to date.
-Galt
Rebol [
Title: "test looper"
File: %test-looper.r
Author: "Galt Barber"
Purpose: {
The person who wanted to have the benefits of foreach,
where you can refer to the element by name alone,
and yet also be able to get the current index,
which is not available with foreach,
motivated me to try to write his "ideal" looper,
which takes an index word accessible in the block.
I am just trying to roll my own enhanced version
of foreach.
It seemed to work pretty well, but I did notice
that 'repeat seems to have a bug, reminiscent
of something I thought I remember was a problem
reported long ago in an earlier version!
}
]
;;; hack to quickly re-load edited source
r: func [][do %test-looper.r]
rec-replace-words: func [
b [block!]
target [word!]
replacement [word!]
][
forall b [
if word? first b [
if (first b) = target [
change b replacement
]
]
if block? first b [
rec-replace-words first b target replacement
]
]
head b
]
ideal-looper: func [
'element [word!]
'index [word!]
s [series!]
code [block!]
/local
eee
iii
ccc
][
ccc: copy/deep code
rec-replace-words ccc element 'eee
rec-replace-words ccc index 'iii
repeat i length? s [
iii: i
eee: s/:i
do ccc
]
]
{
Here is what the output looks like, which is wrong!
>> r
>> do z
1 h h hello
6 none none hello
6 none none hello
6 none none hello
6 none none hello
== false
I thought I may have made a mistake,
but then I thought to try removing
repeat from the definition, and using
while instead, and that did work!
see below!
}
x: "hello"
z: [ ;;; test function, usage is do z
ideal-looper char pos x [
embedit: func [][
prin [pos " " char]
]
embedit
sillyobj: make object! [
q: char
showit: func [][prin [" " q]]
]
sillyobj/showit
prin " "
ideal-looper char pos x [
prin [char]
]
print ""
]
]
{ ;;; this one works, using while instead of repeat!
;;; it is commented out at the moment.
ideal-looper: func [
'element [word!]
'index [word!]
s [series!]
code [block!]
/local
eee
iii
ccc
i
][
ccc: copy/deep code
rec-replace-words ccc element 'eee
rec-replace-words ccc index 'iii
i: 0
while [i < length? s] [
i: i + 1
iii: i
eee: s/:i
do ccc
]
]
}
{ ;;; here is the correct output!
>> r
>> do z
1 h h hello
2 e e hello
3 l l hello
4 l l hello
5 o o hello
== false
>>
}
halt
--mime-boundary-interchange-39b0bccd
Content-Type: application/octet-stream; name="test-looper.r"
Content-disposition: attachment; filename="test-looper.r"
Content-Transfer-Encoding: 7bit
Rebol [
Title: "test looper"
File: %test-looper.r
Author: "Galt Barber"
Purpose: {
The person who wanted to have the benefits of foreach,
where you can refer to the element by name alone,
and yet also be able to get the current index,
which is not available with foreach,
motivated me to try to write his "ideal" looper,
which takes an index word accessible in the block.
I am just trying to roll my own enhanced version
of foreach.
It seemed to work pretty well, but I did notice
that 'repeat seems to have a bug, reminiscent
of something I thought I remember was a problem
reported long ago in an earlier version!
}
]
r: func [][do %test-looper.r]
rec-replace-words: func [
b [block!]
target [word!]
replacement [word!]
][
forall b [
if word? first b [
if (first b) = target [
change b replacement
]
]
if block? first b [
rec-replace-words first b target replacement
]
]
head b
]
ideal-looper: func [
'element [word!]
'index [word!]
s [series!]
code [block!]
/local
eee
iii
ccc
][
ccc: copy/deep code
rec-replace-words ccc element 'eee
rec-replace-words ccc index 'iii
repeat i length? s [
iii: i
eee: s/:i
do ccc
]
]
{
Here is what the output looks like, which is wrong!
>> r
>> do z
1 h h hello
6 none none hello
6 none none hello
6 none none hello
6 none none hello
== false
I thought I may have made a mistake,
but then I thought to try removing
repeat from the definition, and using
while instead, and that did work!
see below!
}
x: "hello"
z: [ ;;; test function, usage is do z
ideal-looper char pos x [
embedit: func [][
prin [pos " " char]
]
embedit
sillyobj: make object! [
q: char
showit: func [][prin [" " q]]
]
sillyobj/showit
prin " "
ideal-looper char pos x [
prin [char]
]
print ""
]
]
{ ;;; this one works, using while instead of repeat!
ideal-looper: func [
'element [word!]
'index [word!]
s [series!]
code [block!]
/local
eee
iii
ccc
i
][
ccc: copy/deep code
rec-replace-words ccc element 'eee
rec-replace-words ccc index 'iii
i: 0
while [i < length? s] [
i: i + 1
iii: i
eee: s/:i
do ccc
]
]
}
{ ;;; here is the correct output!
>> r
>> do z
1 h h hello
2 e e hello
3 l l hello
4 l l hello
5 o o hello
== false
>>
}
halt
--mime-boundary-interchange-39b0bccd--
