A Strong Working Knowledge of K

Dennis Shasha
Courant Institute of Mathematical Sciences
Department of Computer Science
New York University
shasha@cs.nyu.edu
http://cs.nyu.edu/cs/faculty/shasha/index.html

Goal of the GUI

Make it simple to do common operations.
Tie graphics to the data.
We illustrate the GUI facilities through examples of increasing complexity all having to do with game playing.

Basic Scoreboard

Suppose we want to design a scoreboard in k. We have a home team and a guest team and we have two scores.

The strings here indicate operations that occur when a button is hit.

Forms are a kind of display (like a box with numbers). Try playing with the arrangements.


\d scores
home: 0
homeinc:"home+:1"
homeinc..c:`button
guest:0
guestinc:"guest+:1"
guestinc..c:`button

/ go up and set arrangement
\d ^
scores..c: `form / all the scores are a form
scores..a: ,`home `guest  `homeinc `guestinc 
	/ they have a horizontal arrangement
scores..a: `home `guest  `homeinc `guestinc 
	/ they have a vertical arrangement
scores..a: (`home `homeinc;  `guest `guestinc)
	/ they have a mixed arrangement
`show $ `scores / Note that you must have the backquote on scores.
	/ If you do `show $ scores, you won't get that and the arrangement
	/ won't work, but some things will work.
/ As you increment and decrement, you will get different scores.

Note that one sets attributes on the whole scores form in the directory above.

Change Colors

foreground color is the attribute fg.
background is the attribute bg.

\d scores2
home: 0
home..fg: 99 / foreground color should be blue.
homeinc:"home+:1"
homeinc..bg: 99 / background color should be blue.
homeinc..c:`button
guest:0
guestinc:"guest+:1"
guest..fg: 990000 / foreground should be red
guestinc..bg: 990000 / background should be red
guestinc..c:`button

\d ^
scores2..c: `form / all the scores are a form
scores2..a: (`home `homeinc;  `guest `guestinc)
        / they have a mixed arrangement
`show $ `scores2 / Note that you must have the backquote on scores.

Vectors of Scores

Suppose now that we wish to modify a vector of home and guest scores each of size 10.

\d scores3
n: 10
position: 0
position..fg: 9900 / green
home: n # 0
home..fg: 99 / foreground color should be blue.
homeinc:"home[position]+:1"
homeinc..c:`button
guest:n # 0
guest..fg: 990000 / foreground should be red
guestinc:"guest[position]+:1"
guestinc..c:`button
\d ~ / attribute directory of the scores3 directory
	/ Note that this is an alternative to \d ^
	/ followed by scores3..a
a:( `home `guest;  `homeinc `guestinc; `position) / arrangment
\d ^
`show $ `scores3

Other Graphics, e.g. charts

Here, we want the display to be a chart for the home team.


\d scores4
n: 10
position: 0
position..fg: 9900 / green
home: n # 0
home..fg: 99 / foreground color should be blue.
homeinc:"home[position]+:1"
homeinc..c:`button
home..c: `chart
guest:n # 0
guest..fg: 990000 / foreground should be red
guestinc:"guest[position]+:1"
guestinc..c:`button
\d ~ / attribute for the scores4 directory
a:( `home `guest;  `homeinc `guestinc; `position) / arrangment

\d ^
`show $ `scores4

A Betting Game

Let's create a betting game. We agree on a bet amount.
Home presses for a number.
Guest presses for a number.
The higher number wins the bet except that home wins on ties. The bet occurs when the guestflip button is hit.

\d scores5
balance: 0
wager: 1
home: 0
home..fg: 99 / foreground color should be blue.
homeflip:"home:*1 _draw 100"
homeflip..c:`button
guest:0
guest..fg: 990000 / foreground should be red
guestflip:"guest:*1 _draw 100; :[home

Home Has an Edge

Let's redo the betting game using functions. We agree on a bet amount. Home presses for a number. Guest presses for a number. The higher number wins the bet except that home wins on ties. In this case, home also has a 10% edge. The bet occurs when the guestflip button is hit.
```
\d scores6
balance: 0
wager: 1
home: 0
home..fg: 99 / foreground color should be blue.
homeflip:"home:*1 _draw 100"
homeflip..c:`button
guest:0
guest..fg: 990000 / foreground should be red
f:{[wager; home; guest; balance]
  :[home
```

Bank

There are n bank accounts. Each has a randomly chosen name. Triggers are used to update names and balances based on acctid. Another trigger changes the color of the name based on whether the balance is positive or negative.

\d .k
\d bank
n: 100
names: `alice `bob `carol `david 
names,: `eliot `fred `gary `harry `isaac `jack
acctnames: names[n _draw #names]
balances: n # 0
/ fields
name: acctnames[0]
bal: 0
amount: 0
acctid: 0
deposit:"balances[acctid]+: amount; name: acctnames[acctid]; bal: balances[acctid]"
deposit..c:`button
withdraw..fg: 990000 / foreground should be red
withdraw:"balances[acctid]-: amount; name: acctnames[acctid]; bal: balances[acctid]"
withdraw..c:`button
acctid..t: "bal: balances[acctid]; name: acctnames[acctid]"
	/ This updates all other fields whenever acctid is updated.
bal..t: ":[bal < 0; name..fg: 990000; name..fg:99]" 
	/ changes color based on value.
\d ~ / attribute for the bank directory
a:( `acctid `bal `name; `deposit `withdraw; `amount) / arrangement

\d ^
`show $ `bank

Simple Spreadsheet

(Advanced topic) We will write a simple 4 by 10 spreadsheet which processes top-down and left-to-right.

S:D:.+(`a`b`c`d; 4 10#,"") / dictionary of blanks
S[.;`f]: 19 $ D[] / initialize to 19 blanks per cell
S..t: ".[`D;(;);{. y}; S[]]; S[.;`f]: 19 $ D[]" 
	/ at all locations in D update based on S.
	/ Then make the format of S be 19 spaces wide and let it take
	/ the data from D.
`show$`S

Spreadsheet with Fixed Point

(Advanced topic) We will now ensure that the spreadsheet does the correct processing, reaching a fixed point. Not the most efficient, but it works.

S:D:.+(`a`b`c`d; 4 10#,"") / dictionary of blanks
S[.;`f]: 19 $ D[] / initialize to 19 blanks per cell
update:{[]
   oldD: D
   reachedfixed: 0
   while[~ reachedfixed
	.[`D;(;);{. y}; S[]] / note that this affects the global
	if[D ~ oldD; reachedfixed: 1]
	oldD: D ]
}
	
S..t: "update[]; S[.;`f]: 19 $ D[]" 
`show$`S

Check Boxes

Check boxes are sometimes a convenient way to represent information.


n: 100
names: ` $' "abc" ,/: $(!n)
chk: .+(names; n # 0)
chk[~!chk;`c]: `check    / check box did not reflect back to the data
`show $ `chk
/ after you do the selections, can get these.
selected: & chk[!chk] = 1
selectednames: (!chk)[selected]

/ Now show that selected gets updated automatically as you process.
n: 100
names: ` $' "abc" ,/: $(!n)
chk2: .+(names; n # 0)
chk2[~!chk2;`c]: `check    / check box did not reflect back to the data
`show $ `chk2
/ after you do the selections, can get these.
/ chk2..t: " selected: & chk2[!chk2] = 1; selectednames: (!chk2)[selected]; chk2: .+(selectednames; chk2[selectednames]); `show $ `chk2"
chk2..t: " selected: & chk2[!chk2] = 1; selectednames: (!chk2)[selected]"

Fonts (from Mike Whitney)

You can use environment vars KFONT and KLFONT (for data and label fonts, respectively) in the NT environment. Remember that the dimensions of the KFONT must be no less than those for the KLFONT for consistent-looking output, since the K GUI works in units of KFONT height and width.
In NT console, before starting K, you can say
set KFONT=Courier 12
set KLFONT=Arial 11 or some such. (This is similar to the Unix k.)
You can also say, in a K session,
\m fCourier New Bold8
\m lGaramond
You can also say
\m f
\m l
which give you the ability to choose these two fonts from an NT dialog box. This is the most reliable, since the numbers in the earlier examples are width (not pointsize), and on some platforms the height is not scaled appropriately.
One more thing: the KFONT (\m f) must be constant width, or the GUI will not work properly. This confines you to Courier and Courier New, plus perhaps a few others which I have not discovered.