So, you want to build a compiler huh?

Well, You downloaded the right manual. This document will show you how to START a compiler, not build a full one. Please also note that this is NOT for beginners.

Chapter 1	Planning

Okay, now we need to plan what's going to be what. What the language is called, what language does it output, comments, that kind of stuff. Let's start by defining the language:
Language name: Let's call it STAR, okay
Output: What is it going to output? Hmmm... how about Qbasic code. 
Comments: We'll use the % sign for comments
Statements: We'll borrow a couple statements from Qbasic
INPUT for input
PRINT for printing stuff on the screen
PRINTVAR for printing variables on the screen
VAR to declare variables
And > to end the program
Okay now that it's planned out, let's begin.

Chapter 2	Beginning

THE FOLLOWING IS QBASIC CODE:
'----------------------------------------------
compname$ = "STAR to Qbasic compiler"
cls
print compname$
print "1.Begin programming"
print "2.Quit"
input choice
if choice = 1 goto new
endprog:
end
new:
cls
'Stop cutting
'---------------------------------------------
Q: What was that?!!
A: That was the beginning of our compiler. It starts out with a basic menu
 The endprog label is there for future end statements

Now we can continue with the editor
THE FOLLOWING IS QBASIC CODE
'--------------------------------------------------
cls
input "File name? ", filname$
color 10,1
cls
txt:
input "",txt$
if txt$ = "" goto txt
if txt$ = "%" goto comment
if txt$ = "print" goto prnt
if txt$ = "input" goto input
if txt$ = "var" goto var
if txt$ = "printvar" goto prntvar
if txt$ = ">" goto ending
'Stop cutting
'---------------------------------------------------
Okay, we now have our commands laid out. Now, we will have the compiler turn them  into Qbasic code

THE FOLLOWING IS QBASIC CODE
'---------------------------------------------------
print "Syntax error"
print ""
play "d"
goto txt
comment:
input txt$
close
open filname$ for append as #1
print #1, "'";txt$
close
goto txt

prnt:
input txt$
close
open filname$ for append as #1
print #1, "PRINT ";chr$(34);txt$;chr$(34)
close
goto txt

input:
input txt$
close
open filname$ for append as #1
print #1, "Input ";txt$
close
goto txt
'Stop cutting
'--------------------------------------------------
Now we have the basic PRINT, COMMENT and INPUT functions.
Note: I'm not sure if chr$(34) = "" so if I'm wrong I'M SORRY!
Note that the compiler saves to the program after every line. 
Now, we finish our compiler

THE FOLLOWING IS QBASIC CODE
'-----------------------------------------------------------
var:
input txt$
close
open filname$ for append as #1
print #1, txt$
close
goto txt

prntvar:
input txt$
close
open filname$ for append as #1
print #1, "PRINT ";txt$
close
goto txt

ending:
close
open filname$ for append as #1
print #1, "'>"
goto endprog
'Stop cutting
'---------------------------------------------------------
Well, there ya have it. Test this compiler with this program

%
The classic (and cheesy) Hello world program
Print
Hello world!
>

Name the file HELLO.BAS because it's gonna be compiled by Qbasic eventually.
This is about as simple as it gets. The CRAPPIEST and EASIEST compiler to ever be built. But it works (or at least it should.). There is a downloadable example of this.
It's called the Saturn 1 to MOONROCK compiler version xxx, where xxx is the version.
Download it from:
www.qb4all.com in the Compilers section.
Moonrock comes with it.  Version 0.02 SUCKS but version 0.05 is a little better.
Well, that just about ends it. Bye Bye!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Made on AUGUST 3rd 2004 by BRENDEN "b-man" HOMAN