04a readme and corrections

03/README.md

@@ -165,4 +165,4 @@ you need to make sure you store away any information you'll need after the funct
 And the language definitely won't be as nice to use as something with real variables. But overall,
 I'm very happy with this compiler, especially considering it's written in a language with 2-letter label
 names.
-
+With that, let's move on to the [next stage](../04a/README.md).

04a/Makefile

@@ -1,6 +1,8 @@
-all: out03
+all: out03 out04a README.html
 out03: in03 ../03/out02
 	../03/out02
+out04a: out03 in04a
+	./out03 in04a out04a
 %.html: %.md ../markdown
 	../markdown $<
 clean:

04a/README.md

@@ -0,0 +1,23 @@
+# stage 04a
+
+Rather than a compiler, this stage only consists of a simple [preprocessor](https://en.wikipedia.org/wiki/Preprocessor).
+In the future, we'll run our code through this program, then run its output
+through a compiler.
+
+It take lines like:
+```
+#define THREE d3
+```
+and then replaces `THREE` anywhere in the rest of the code with `d3`.
+I've provided `in04a` as a little example.
+Unlike previous programs, you can control the input and output file names
+without recompiling it. So to compile the example program:
+```
+make out03
+./out03 in04a out04a
+```
+
+Although it seems simple, this program will be very useful:
+it'll let us define constants and it'll work in any language.
+There really isn't much else to say about this program. With that,
+we can move on to [the next stage](../04b/README.md) which should be more exciting.

04a/in03

@@ -68,7 +68,7 @@ R=:line
 		; check if we reached the end of the line
 		C=1R
 		D=xa
-		?C=A:read_line
+		?C=D:read_line
 		; increment R, keep looping
 		R+=d1
 		!:process_line_loop

04a/in04a

@@ -1,7 +1,3 @@
-A+B=hello A adfhsakjfhjksah+B
-#define COLON d1
-#define SEMICOLON d2
-#define COMMA d3
-
-A=COLON
-1B=A
+#define H Hello,
+#define W world
+H W!

bootstrap.sh

@@ -39,7 +39,7 @@ cd ..
 
 echo 'Processing stage 01...'
 cd 01
-rm -f out0[01]
+rm -f out*
 make -s out01
 if [ "$(./out01)" != 'Hello, world!' ]; then
 	echo_red 'Stage 01 failed.'
@@ -50,7 +50,7 @@ cd ..
 
 echo 'Processing stage 02...'
 cd 02
-rm -rf out0[12]
+rm -f out*
 make -s out02
 if [ "$(./out02)" != 'Hello, world!' ]; then
 	echo_red 'Stage 02 failed.'
@@ -60,7 +60,7 @@ cd ..
 
 echo 'Processing stage 03...'
 cd 03
-rm -rf out0[23]
+rm -f out*
 make -s out03
 if [ "$(./out03)" != 'Hello, world!' ]; then
 	echo_red 'Stage 03 failed.'
@@ -68,5 +68,15 @@ if [ "$(./out03)" != 'Hello, world!' ]; then
 fi
 cd ..
 
+echo 'Processing stage 04a...'
+cd 04a
+rm -f out*
+make -s out04a
+if [ "$(cat out04a)" != "$(printf '\n\nHello, world!')" ]; then
+	echo_red 'Stage 04a failed.'
+	exit 1
+fi
+cd ..
+
 
 echo_green 'all stages completed successfully!'