I tried using the find function to check for the occurrence of the string "ll" in the string "hello", but it returns "ll" instead of true or false:
"This prints 'll'"
print find "hello" "ll"
Does REBOL's standard library have any functions to check if a string contains another string?
Try this
>> print found? find "hello" "ll"
true
>> print found? find "hello" "abc"
false
#ShixinZeng is correct that there is a FOUND? in Rebol. However, it is simply defined as:
found?: function [
"Returns TRUE if value is not NONE."
value
] [
not none? :value
]
As it is equivalent to not none?...you could have written:
>> print not none? find "hello" "ll"
true
>> print not none? find "hello" "abc"
false
Or if you want the other bias:
>> print none? find "hello" "ll"
false
>> print none? find "hello" "abc"
true
Intended to help with readability while using FIND. However, I don't like it because it has confusing behavior by working when not used with FIND, e.g.
>> if found? 1 + 2 [print "Well this is odd..."]
Well this is odd...
Since you can just use the result of the FIND in a conditional expression with IF and UNLESS and EITHER, you don't really need it very often...unless you are assigning the result to a variable you really want to be boolean. In which case, I don't mind using NOT NONE? or NONE? as appropriate.
And in my opinion, losing FOUND? from the core would be fine.
as written in prior answers find gives you back already a result you can use in conditional expressions.
>> either find "hello" "ll" [
[ print "hit"
[ ] [
[ print "no hit"
[ ]
hit
or in a more rebolish way
>> print either find "hello" "ll" [ "hit"] [ "no hit"]
hit
But you can also use to-logic on the result giving you true or false
>> print to-logic find "hello" "ll"
true
>> print find "hello" "lzl"
none
>> print to-logic find "hello" "lzl"
false
Related
Let's say I have a conditional Tcl expression that is a boolean combination of steps.
Will the expression always be evaluated left to right (excluding parentheses)?
If the expression becomes true will the rest of the evaluation stop?
I have this piece of code that parses a file and conditionally replaces stuff in the lines.
set fp [ open "file" ]
set data [ read $fp ]
close $fp
foreach line [ split $data \n ] {
if { $enable_patch && [ regsub {<some_pattern>} $line {<some_other_pattern>} line ]} {
puts $outfp $line
<do_some_more_stuff>
}
}
So my issue here is that unless enable_patch is true, I don't want the line to be modified. Now my test shows that the code is deterministic in Tcl 8.5 on Linux. But I am wondering if this would break under other conditions/ versions/ OSes.
Yes, the || and && operators are "short-circuiting" operators in TCL. That means you can rely on them being evaluated left-to-right, and that evaluation will stop as soon as the value of the expression is known.
When I call f without parameter, I got the error Script Error: if does not allow unset! for its then-blk argument why ?
f: func['p [string! unset!]][
if unset? 'p print "unset"
]
'p evaluates to the word p. In order to test the type of the value referred by p, you need to use :p and provide a proper body block for if:
f: func ['p [string! unset!]][
if unset? :p [print "unset"]
]
>> f "123"
== none
>> f
unset
I'm trying to change the value of a Boolean variable using expression in bash script (Debian Jessie) but it's not working as intended!
Here is my code
vld=true
while ! [ $vld ]
do
echo "Enter a number: [1-30]:"
read myinput
$vld=[ $myinput -ge 1 ] && [ $myinput -le 30 ]
done
echo "Your number is $myinput
When I this script it says:
8: ./test.sh true=[: not found
Then it keeps on the loop as the variable is not receiving the result of the expression but is used itself!
Newbie question here...
I'd like to write the output of the "what" function to a text file.
So here is what I have done:
I've created a variable called "text" and assigned the output of "what" to it
text: [what]
Now I want to write the content of the "text" variable to a txt file...
Any help is appreciated. Thanks in advance!
the easiest way to write the output of statements to a file is to use
echo %file.log
what
with echo none you end this
>> help echo
USAGE:
ECHO target
DESCRIPTION:
Copies console output to a file.
ECHO is a function value.
ARGUMENTS:
target -- (Type: file none logic)
(SPECIAL ATTRIBUTES)
catch
Unfortunately there is not really a value returned from the what function:
Try the following in the console:
print ["Value of `what` is: " what]
So write %filename.txt [what] will not work.
Instead, what you could do is to look at the source of what
source what
which returns:
what: func [
"Prints a list of globally-defined functions."
/local vals args here total
][
total: copy []
vals: second system/words
foreach word first system/words [
if any-function? first vals [
args: first first vals
if here: find args /local [args: copy/part args here]
append total reduce [word mold args]
]
vals: next vals
]
foreach [word args] sort/skip total 2 [print [word args]]
exit
]
See that this function only prints (it doesn't return the values it finds) We can modify the script to do what you want:
new-what: func [
"Returns a list of globally-defined functions."
/local vals args here total collected
][
collected: copy []
total: copy []
vals: second system/words
foreach word first system/words [
if any-function? first vals [
args: first first vals
if here: find args /local [args: copy/part args here]
append total reduce [word mold args]
]
vals: next vals
]
foreach [word args] sort/skip total 2 [append collected reduce [word tab args newline]]
write %filename.txt collected
exit
]
This function is a little hackish (filename is set, but it will return what you want). You can extend the function to accept a filename or do whatever you want. The tab and newline are there to make the file output prettier.
Important things to notice from this:
Print returns unset
Use source to find out what functions do
write %filename value will write out a value to a file all at once. If you open a file, you can write more times.
Fairly elementary: use write if you just want to save some text, read to recover it; use save if you want to store some data and use load to recover it.
>> write %file.txt "Some Text"
>> read %file.txt
== "Some Text"
>> text: [what]
>> save/all %file.r text
>> load %file.r
== [what]
You can get more information on each word at the prompt: help save or view online: load, save, read and write.
It is possible to overide rebol system words like print, make etc., so is it possible to do the same with the path operator ? Then what's the syntax ?
Another possible approach is to use REBOL meta-programming capabilities and preprocess your own code to catch path accesses and add your handler code. Here's an example :
apply-my-rule: func [spec [block!] /local value][
print [
"-- path access --" newline
"object:" mold spec/1 newline
"member:" mold spec/2 newline
"value:" mold set/any 'value get in get spec/1 spec/2 newline
"--"
]
:value
]
my-do: func [code [block!] /local rule pos][
parse code rule: [
any [
pos: path! (
pos: either object? get pos/1/1 [
change/part pos reduce ['apply-my-rule to-block pos/1] 1
][
next pos
]
) :pos
| into rule ;-- dive into nested blocks
| skip ;-- skip every other values
]
]
do code
]
;-- example usage --
obj: make object! [
a: 5
]
my-do [
print mold obj/a
]
This will give you :
-- path access --
object: obj
member: a
value: 5
--
5
Another (slower but more flexible) approach could also be to pass your code in string mode to the preprocessor allowing freeing yourself from any REBOL specific syntax rule like in :
my-alternative-do {
print mold obj..a
}
The preprocessor code would then spot all .. places and change the code to properly insert calls to 'apply-my-rule, and would in the end, run the code with :
do load code
There's no real limits on how far you can process and change your whole code at runtime (the so-called "block mode" of the first example being the most efficient way).
You mean replace (say)....
print mold system/options
with (say)....
print mold system..options
....where I've replaced REBOL's forward slash with dot dot syntax?
Short answer: no. Some things are hardwired into the parser.