posted 29 May 2013 04:53            

I just joined this amazing environment and like probably most of you have I'm reading the manual.
One of the things I seems not to fully understand is the concept of "Keywords".

At page 225 at the bottom the book states: "A keyword message takes two or more arguments (all EventExpressions), and is composed of a sequence of keywords, each of which is followed by a colon ( and an argument."
Thats fine, but considering the colon rule above I don't understand why a Keyword message like "60 nn hz" is not "60 nn: hz:"

Could anybody clear this out for me?

Tazio

posted 30 May 2013 23:43            

I'm no Smalltalk expert (Smalltalk being the language that Capytalk is derived from - they share syntax, and this question relates to basic Smalltalk syntax) - I'm sure there are a lot of people more qualified to answer this question here, but I'll give it a shot.

Keyword messages are one of several different kinds of message, in which the message involves one or more arguments. Take for example the Capytalk message:

!KeyNumber gt: 60

Here the receiver (the recipient of the message) is the hot parameter !Keynumber, the message is gt: (greater than), and the parameter involved is 60. Basically it's saying something like "given the variable number !KeyNumber, tell me when it is greater than 60." So when !KeyNumber is greater than 60, the whole expression equals 1, and when !KeyNumber is not greater than 60, the expression equals 0.

If there's more than one parameter, the Keyword expression takes form:
[Receiver] keywordPart1: argument keywordPart2: argument.

Together, what I'm calling keywordPart1: and keywordPart2: are a single message which takes 2 arguments.

For example, here is the message true: false: in use:

[comparison expression] true: 0 false: !KeyNumber

Pasting in our other expression for the [comparison expression], you could turn this into:

((!KeyNumber gt: 60) true:0 false:!KeyNumber)

Now when our original expression asking if !KeyNumber is greater than 60 becomes a 1 (true), that triggers the true: part of the message, which makes the entire expression equal to the argument 0. If, however, !KeyNumber is 60 or under, the false: argument is invoked, and !KeyNumber is returned (or, !Keynumber is allowed to pass through unaltered, so that effectively you've just turned !KeyNumber values above 60 to 0).

Hope that makes some sense.

The other message type you mention is binary, which don't have any arguments.

In the expression "60 nn" the receiver, the NUMBER 60, is converted by the message "nn" into a different type of object, a NOTE NUMBER (basically a midi note number, where 60 equals middle c). The expression "hz", when sent to a receiver that is a note number, converts the note number into hz. So it wouldn't be 60 nn: hz, because hertz isn't functioning as an argument in the expression - the whole expression is actually one binary receiver/message pair, followed by another receiver/message pair. The first pair is "60 nn," which is converting a number 60 into a note number 60, and the second receiver/message pair is the note number 60, which is receiving the message from hz, converting it to hz (which I believe rounds to 261 hz).

Hope that helps.

You might try looking online for resources explaining Smalltalk syntax. I just found a bunch of videos that I should watch at:
http://smalltalk.org/videos/video_Basics_Block.html

Good luck!

Phil

[This message has been edited by Phi Curtis (edited 30 May 2013).]

posted 31 May 2013 11:00            

There are also some examples and explanations in Kyma X Revealed which you can access from the Help menu in Kyma and search for "keyword". For example on page 225:

quote:

---

A unary message has one argument (the receiver), for example

!Fader negated

A binary message has two arguments (also EventExpressions), for example

!Fader1 + !Fader2

A keyword message takes two or more arguments (all EventExpressions), and is composed of a sequence of keywords, each of which is followed by a colon ( :) and an argument. The number of keywords equals the number of arguments, and the ordering of the keywords is an essential property of the message. In other words, all of the keywords taken together form the “keyword message”. For example, if you wanted to define the CapyTalk keyword message

!Trig bpm: !BPM dutyCycle: !Duty

with all of the keywords combined to form the name of the function as a C function, it would probably come out looking something like this:

bpmWithDutyCycle (!Trig, !BPM, !Duty)

---

posted 31 May 2013 19:54            

I think what can be initially confusing about a message like "1 bpm: 60" is that the receiver, 1, is just a number (a number acting as a trigger, but still just a number). The idea that numbers can be made to launch a repeating pulse seems a little abstract.

posted 31 May 2013 20:27            

"I think what can be initially confusing about a message like "1 bpm: 60" is that the receiver, 1, is just a number (a number acting as a trigger, but still just a number). The idea that numbers can be made to launch a repeating pulse seems a little abstract."

That's true. Maybe it would be more clear if we started with an example where the metronome can be turned on or off, so

!Gate bpm: 60

and then explain that a !Gate value of 0 is off and !Gate value of 1 is on, and only then proceed to:

1 bpm: 60

as a gate that is permanently stuck in the ON position.

posted 20 June 2013 20:01            

This aspect of 1 !BPM has had me wondering why it was so since the first time I saw it.

Finally the penny drops.