Grammer2/docs/tutorials/controlflow.md

Control Flow

If you already know how to use BASIC control flow you can skip to the next section on Grammer's control flow perks. If not, then read up on this section before moving on. There is a lot of info to retain.

Control Flow is the ability to control the flow of your program. We do this by using commands such as If, While, Repeat, For, and Goto/Lbl.

Code Blocks and Loops

Using If-Then-Else

If I use If in a program Then, if the statement is true then the following code will be executed until the corresponding End token is reached.

Code:

If 1
Then
<<<code to execute>>>
End

Note: In Grammer, true simply means non-zero, while 0 is false, as in TI-BASIC.

However, as in TI-BASIC, if we only need to execute one line of code, Then and End can be omitted.

Code:

If 1
<<<code to execute>>>

If I use an If, Then, and Else in a single block then if the statement is true, the following code will be executed until the Else token. If the statement is false the code under Else will be executed until the corresponding End token is reached.

Code:

If 0
Then
<<<code to execute if true>>>
Else
<<<code to execute if false>>>
End

A statement is any block of math to be used after the If. I used 1 and 0 as to represent not just how If sees the equation but all control flow commands. However, you can use a variable such as A or an expression like A>1 which would return 1 if A is greater than 1 and 0 if less than A.

While loops

While loops repeat while the statement is true.

Repeat loops

For loops

Pause & Pause If

A pause is pretty much like a loop. The only difference is the way that it loops. In Grammer Pause can be used in 3 ways, so long as you don't count the ! modifier. The syntax is as follows...

Pause xx   ;Pauses for approx. xx/100 seconds(useful for delays)
Pause If   ;Pauses while a statement is true
Pause      ;Pauses until [ENTER] is pressed(same as BASIC)

Pause xx

Pause xx is kind of like For xx:End It repeats that many times. Don't get the 2 mixed up though! Let's say you were displaying text and you want to display it in intervals. Pause xx will allow you to do that.

Code:

.0:Return
102→A
ClrDraw
Text(°"Super Cool Text!
DispGraph
Pause A       ;This pauses for about 102/100 of a second.
Text(°" Using Pause !
Pause 50
Text(°" Oh and pvars!
Stop

Pause

Pause is kind of like doing Repeat getKey(9:End. It loops over and over until you press [ENTER] Its best use is probably waiting for the user to press Enter... ;P

Code:

.0:Return
ClrDraw
Text(°"Press Enter
DispGraph
Pause
Stop

Pause If

Pause If is a way to use conditional statements with Pause. Please remember that you can't exit a statement that is always true without pressing [ON]. There are too ways to use this (as far as I'm concerned). The main use for this is to pause and either wait for a keypress, or wait for the keypress to be done.

Code:

.0:Return
ClrDraw
Text(°"Press [MODE]
!Pause If getKey(55              ;Note the use of the ! modifier
Text(10,0,"Thanks!
Stop

You might also want to wait for an interrupt to signal for some reason. In this example, Pause If S looks like it should loop forever, but the interrupt is decrementing S and eventually S will be 0, causing the Pause If to finish.

Code:

.0:Return
FuncLbl "APPLE
100→S
Pause If S
Text(10,0,"Continues executing once S equals 0.
Stop
.APPLE
ClrDraw
Text('°S
GetDec(S
DispGraph
End

Note: This works because interrupts are set. Without them this code wouldn't really have a way to exit.

Labels and Subroutines

Lbl

Return

Goto

▶Nom(

Line Jumping With ln(

prgm

Passing Parameters

Asm(

AsmPrgm

Others

expr(

Interrupts

Interrupts are pretty handy when you want a task to be able to run separately from your main code. For example, with grayscale, maybe you want to be able to pause but still have grayscale going:

.0:Return

FuncLbl "Draw         ;Setup the interrupt to execute .Draw

SetBuf(°gbuf'→B       ;Set up the gray/secondary buffer
2→SetBuf(             ;Set 4-level grayscale

Rect(0,0,16,8         ;Draw a 16x8 rect on the main buffer
Rect(0,0,8,16,1,B     ;Draw an 8x16 rect on the secondary buffer

!Pause If getKey      ;Now wait for a keypress
Stop

.Draw
DispGraph
End

This still does DispGraph while the program is Paused!

Execute a line of code