|X Y A B C D|
Y:= 7.
X:= 6.
(X = Y)
ifTrue: [X := 0]
ifFalse:[X := 1].
B:=2.
C:=5.
D:=1.
A:= (B squared)*(C-D).
"print both A and X to screen here"
Simple enough little smalltalk example. I'm just curious how I can get this to print X and A as outputs? is there any way to do it w/o having to perform a 'print it' on the top 6 lines and a seperate 'print it' on the bottom 5 lines? if it could print out on just a 'do it' or a single 'print it' please let me know!
You should define what is "printing" and what is X and A.
If "printing" is a result of the "print it" action, then you are talking in general about returning X and A, as "print it" prints the return result of the selected code. This way you have to think about an object which will represent X and A. For this object you can define a printString method or printOn: and get the result printed. Or you can cheat a bit and return a point by doing X#A.
If you are talking about actually printing the thing somewhere then you have to tell more about where do you want to do it. You can print it in Transcript or similar, but there you have to explicitly send a message to the Transcript with what you want to be printed.
Now if you want to use this for "debugging/testing" reasons, it can be easier to go with "inspect it". In your code you can send inspect messages to the objects that you want to look at, and during the execution inspectors will open showing this objects.
Also I encourage you to follow conventions and make your variable names start with lowercase letter.
Smalltalk has no equivalent of print() or println() or the like, since most Smalltalk environments live in a window environment. There are ways to write output to stdout or std error, but this is very dialect specific.
One of the places that somehow replaces stdout in most dialects is a place/stream/window called Transcript, in most dialects this is the window that launches first when your start the IDE.
To write something there you simple do:
Transcript show: 'A=', A asString, ' ; X=', X asString.
(please note that in Smalltalk, Strings and Collections are concatenated with a comma)
You can also write a newLine by sending the message cr to the Transcript like so:
Transcript cr.
Does this answer your question?
A hint for further learning/investigation: Transcript is just a Variable that holds a Stream object. show: is a message that writes some String onto that Stream. asString is a method that returns a String representation of an object.
Related
I found this one liner which joins same lines from multiple files.
How to add a space between two lines?
If line 1 from file A is blue and line 1 from file B is sky, a get bluesky,
but need blue sky.
say $_ for [Z~] #*ARGS.map: *.IO.lines;
This is using the side-effect of .Str on a List to add spaces between the elements:
say .Str for [Z] #*ARGS.map: *.IO.lines
The Z will create 2 element List objects, which the .Str will then stringify.
Or even shorter:
.put for [Z] #*ARGS.map: *.IO.lines
where the .put will call the .Str for you and output that.
If you want anything else inbetween, then you could probably use .join:
say .join(",") for [Z] #*ARGS.map: *.IO.lines
would put comma's between the words.
Note: definitely don't do this in anything approaching real code. Use (one of) the readable ways in Liz's answer.
If you really want to use the same structure as [Z~] – that is, an operator modified by the Zip meta-operator, all inside the Reduce meta-operator – you can. But it's not pretty:
say $_ for [Z[&(*~"\x20"~*)]] #*ARGS.map: *.IO.lines
Here's how that works: Z can take an operator, so we need to give it an operator that concatenates two strings with a space in between. But there's no operator like that built in. No problem – we can turn any function into an infix operator by surrounding it with [ ] (the infix form).
So all we need is a function that joins two strings with a space between them. That also doesn't exist, but we can create one: * ~ ' ' ~ *. So, we should be able to shove that into our infix form and pass the whole thing to the Zip operator Z[* ~ ' ' ~ *].
Except that doesn't work. Because Zip isn't really expecting an infix form, we need to give it a hint that we're passing in a function … that is, we need to put our function into a callable context with &( ), which gets us to Z[&(* ~ ' ' ~ *)].
That Zip expression does what we want when used in infix position – but it still doesn't work once we put it back into the Reduce/[ ] operator that we want to use. This time, the problem is due to something that may or may not be a bug – even after discussing it with jnthn on github, I'm still not sure whether this behavior is intended/correct.
Specifically, the issue is that the Reduction meta-operator doesn't allow whitespace – even in strings. Thus, we need to replace * ~ ' ' ~ * with *~"\c[space]"~* or *~"\x20"~* (where \x20 is the hex value of in Unicode/ASCII). Since we've come this far into obfuscated code, I figure we might as well go all the way. And that gets us back to
say $_ for [Z[&(*~"\x20"~*)]] #*ARGS.map: *.IO.lines
Again, I'm not recommending that you do this. (And, if you do, you could at least make it slightly more readable by saving the * ~ ' ' ~ * function as a named variable in the previous line, which at least gets you whitespace. But, really, just use one of Liz's suggestions).
I just thought this gives a useful window into some of the darker and more interesting corners of Raku's strangely consistent behavior.
In Perl 6, what is the difference between print, put and say?
I can see how print 5 is different, but put 5 and say 5 look the same.
put $a is like print $a.Str ~ “\n”
say $a is like print $a.gist ~ “\n”
put is more computer readable.
say is more human readable.
put 1 .. 8 # 1 2 3 4 5 6 7 8
say 1 .. 8 # 1..8
Learn more about .gist here.
———
More accurately, put and say append the value of the nl-out attribute of the output filehandle, which by default is \n. You can override it, though. Thanks Brad Gilbert for pointing that out.
Handy Perl 6 FAQ: How and why do say, put and print differ?
The most obvious difference is that say and put append a newline at the end of the output, and print does not.
But there's another difference: print and put converts its arguments to a string by calling the Str method on each item passed to, say uses the gist method instead. The gist method, which you can also create for your own classes, is intended to create a Str for human interpretation. So it is free to leave out information about the object deemed unimportant to understand the essence of the object.
...
So, say is optimized for casual human interpretation, dd is optimized for casual debugging output and print and put are more generally suitable for producing output.
...
I have been trying to redefine the printOn method by using this code:
coordinates do: [:elem | aStream print: elem] separatedBy: [aStream print: ' ,']
where "coordinates" stands for the name of the collection (OrderedCollection), but i was expecting to print this when calling to Transcript show:
(2/2) ,(1/1) ,(3/3) ,(-4/4)
I got this instead:
(2/2)','(1/1)','(3/3)','(-4/4)
i. e the quotes was printed as well.
I have tried to play with it, defining a local variable and use it, etc.
Nothing worked.
Don't use #print: to print strings. Use #nextPutAll: to be safe (works for all collections). #print: writes a string representation on the stream and surrounds the argument with quotes, that's why you get quotes in the output.
i want to do something like this: Transcript show: '\n'. how?
Use the following:
Transcript cr
You can use it after a value via a cascade:
Transcript show: 123; cr
From my (long) experience, missing character escapes are one of the few things that are missing in Smalltalk. For streaming, solutions using cr, tab etc. are ok.
However, if you need a particular control character in a string, this may be ugly and hard to read (using "streamContents:", or "withCRs" to add a newLine). Alternatively, you may want to use one of the (non-standard) string expansion mechanisms. For example, in VisualWorks or Smalltalk/X, you can write (if I remember correctly):
'someString with newline<n>and<t>tabs' expandMacros
or even with printf-like slicing of other object's printStrings:
'anotherString<n><t>with newlines<n>and<t>tabs and<p>' expandMacrosWith:(Float pi)
I guess, there is something similar in Squeak and V'Age as well.
But, be aware: these expansions are done at execution time. So you may encounter a penalty when heavily using them on many strings.
The character itself can be reached as Character cr. So, you could also do this:
Transcript show: 'Bla! , Character cr asString.
But of course,
Transcript show: 'Bla!' ; cr.
is way more elegant.
What I do as a convenience is add a method "line" to the String class:
line
^self, String lf
Then you can just say obj showSomething: 'Hello world!' line.
Or call it newline, endl, lf, etc...
Let's say I have
o: context [
f: func[message /refine message2][
print [message]
if refine [print message 2]
]
]
I can call it like this
do get in o 'f "hello"
But how can I do for the refinement ? something like this that would work
>> do get in o 'f/refine "hello" "world"
** Script Error: in expected word argument of type: any-word
** Near: do get in o 'f/refine
>>
I don't know if there's a way to directly tell the interpreter to use a refinement in invoking a function value. That would require some parameterization of do when its argument is a function! Nothing like that seems to exist...but maybe it's hidden somewhere else.
The only way I know to use a refinement is with a path. To make it clear, I'll first use a temporary word:
>> fword: get in o 'f
>> do compose [(to-path [fword refine]) "hello" "world"]
hello
world
What that second statement evaluates to after the compose is:
do [fword/refine "hello" "world"]
You can actually put function values into paths too. It gets rid of the need for the intermediary:
>> do compose [(to-path compose [(get in o 'f) refine]) "hello" "world"]
hello
world
P.S. you have an extra space between message and 2 above, where it should just be message2
Do this:
o/('f)/refine "hello" "world"
Parens in a path expression are evaluated if they correspond to object field or series pick/poke index references. That makes the above code equivalent to this:
apply get in o 'f ["hello" true "world"]
Note that apply arguments are positional, so you need to know the order the arguments were declared in. You can't do that trick with the function refinements themselves, so you have to use apply or create path expressions to evaluate if you want to parameterize the refinements of the function call.
Use the simple path o/f/refine