basic Basic

basic Basic is a one pass basic Basic compiler for a basic dialect of Basic.

It supports the following commands:

command	syntax	description
LET	cnum LET v e	Assigns variable v to the value of expression e
GOTO	cnum GOTO ‘cnum	Goes to the command numbered ‘cnum
IF	cnum IF p THEN t ELSE e	if p is not 0 execute command t else execute command e
PLOT	cnum PLOT x y color	Fills the pixel at x,y with the given color
FOR	cnum FOR i init TO end …new lines containing commands… cnum NEXT i	Repeats the commands between the FOR and the NEXT while end >= i. i is incremented once in every iteration

Example

look at pirate-ship.bas for an example. It will produce the following image

LET red 13583410
LET lightRed 16541523
LET blue 7574225 
LET white 16777215
LET brown 7355966
LET lightBrown 9393750
LET grey 10921638
LET lightGrey 12105912

LET height 800
LET width 800
LET seaLevel (height/4)*3

FOR x 0 TO width-1
FOR y 0 TO height-1
IF y > seaLevel THEN LET color blue ELSE LET color white
PLOT x y color
NEXT y
NEXT x

LET startAt width/20
LET diagonalLen width/6
LET sink 25
LET borderWidth 4

FOR c 0 TO diagonalLen

LET y (seaLevel +  c) - diagonalLen + sink

FOR f startAt + c TO width - (startAt + c) 
PLOT f y brown
NEXT f
LET x startAt + c
FOR depth 0 TO borderWidth
LET ywithDepth y + depth
PLOT x ywithDepth lightBrown
PLOT width - x ywithDepth lightBrown
NEXT depth

NEXT c


LET lowestX (startAt + diagonalLen)
LET y seaLevel + sink
FOR x lowestX TO (width - lowestX)
FOR depth 0 TO borderWidth
PLOT x y + depth   lightBrown
NEXT depth
NEXT x

LET boatTop seaLevel - diagonalLen + sink

FOR x startAt TO (width - startAt)
FOR depth 0 TO borderWidth
PLOT x boatTop-depth lightBrown
NEXT depth
NEXT x

LET poleXStart startAt*4+10
LET poleWidth 5
FOR y height/3-50 TO boatTop-borderWidth-1

FOR depth 0 TO 3
PLOT poleXStart-depth y lightGrey
PLOT poleXStart-depth y lightGrey
NEXT depth

FOR depth 0 TO poleWidth
PLOT poleXStart+depth y grey
NEXT depth
NEXT y

LET flagEnd width/2 + poleXStart 
FOR y height/3-50 TO boatTop-80
FOR x poleXStart + poleWidth + 1 TO flagEnd
PLOT x y red
NEXT x
NEXT y

FOR depth 0 TO 2
FOR x poleXStart + poleWidth + 1 TO flagEnd
PLOT x y+depth lightRed
NEXT x
NEXT depth

LET red 16711680 
LET blue 255
LET width 800
LET halfWidth width/2

FOR c 0 TO width-1
IF halfWidth > c THEN LET color red ELSE LET color blue
PLOT (width-c) (width-c) color
PLOT c (width-c) color
PLOT halfWidth c color
PLOT halfWidth+1 c color
PLOT c halfWidth color
PLOT c halfWidth+1 color
NEXT c

Usage

The following command will compile example.bas to UVM assembly.

clj -M basic.clj example.bas

You will need to download UVM and use it to run the generated assembly.

Reqs

• UVM (https://github.com/maximecb/uvm)
• clojure