+# Overview #
+
+This example starts with the `Hello, world!` example from Wikipedia's
+Whitespace page, gradually rewriting it to use the ASCII string feature of the
+VVhitespace compiler and the `printf` subroutine from the stdlib.
+
+# "Hello, World!" in VVhitespace #
+
+Wikipedia's `Hello, World!` example is reproduced below. It follows a simple
+form, pushing an integer corresponding to an ASCII character onto the stack and
+then printing it with an IO instruction, repeating this two part process for
+each character before terminating with the final instruction.
+
+ SSSTSSTSSSN | Push +72 (ASCII H)
+ TNSS | Output character
+ SSSTTSSTSTN | Push +101 (ASCII e)
+ TNSS | Output character
+ SSSTTSTTSSN | Push +108 (ASCII l)
+ TNSS | Output character
+ SSSTTSTTSSN | Push +108 (ASCII l)
+ TNSS | Output character
+ SSSTTSTTTTN | Push +111 (ASCII o)
+ TNSS | Output character
+ SSSTSTTSSN | Push +44 (ASCII ,)
+ TNSS | Output character
+ SSSTSSSSSN | Push +32 (ASCII space)
+ TNSS | Output character
+ SSSTTTSTTTN | Push +119 (ASCII w)
+ TNSS | Output character
+ SSSTTSTTTTN | Push +111 (ASCII o)
+ TNSS | Output character
+ SSSTTTSSTSN | Push +114 (ASCII r)
+ TNSS | Output character
+ SSSTTSTTSSN | Push +108 (ASCII l)
+ TNSS | Output character
+ SSSTTSSTSSN | Push +100 (ASCII d)
+ TNSS | Output character
+ SSSTSSSSTN | Push +33 (ASCII !)
+ TNSS | Output character
+ SSSTSTSN | Push +10 (ASCII '\n')
+ TNSS | Output character
+ NNN | Terminate program
+
+If we push the string onto the stack in reverse order we can rearrange the
+code as shown below. Now we're first pushing all the ASCII characters onto the
+stack, then printing them all at once.
+
+ SSSTSTSN | Push +10 (ASCII '\n')
+ SSSTSSSSTN | Push +33 (ASCII !)
+ SSSTTSSTSSN | Push +100 (ASCII d)
+ SSSTTSTTSSN | Push +108 (ASCII l)
+ SSSTTTSSTSN | Push +114 (ASCII r)
+ SSSTTSTTTTN | Push +111 (ASCII o)
+ SSSTTTSTTTN | Push +119 (ASCII w)
+ SSSTSSSSSN | Push +32 (ASCII space)
+ SSSTSTTSSN | Push +44 (ASCII ,)
+ SSSTTSTTTTN | Push +111 (ASCII o)
+ SSSTTSTTSSN | Push +108 (ASCII l)
+ SSSTTSTTSSN | Push +108 (ASCII l)
+ SSSTTSSTSTN | Push +101 (ASCII e)
+ SSSTSSTSSSN | Push +72 (ASCII H)
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ NNN | Terminate program
+
+As a convenience, the VVhitespace compiler will accept `A""` syntax, generating
+a sequence of `PUSH` instructions, just like the prior examples, that places a
+null-terminated ASCII string on the stack. This allows us to shorten the
+program. Like before, the start of the string is closest to the top of the
+stack. Unlike before, there is now a null terminator at the end of the string.
+For now, we'll just leave that on the stack when the program terminates.
+
+ A"Hello, world!\n"
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ TNSS | Output character
+ NNN | Terminate program
+
+Finally, we will use `printf` from the stdlib to shorten that mass of IO
+instructions. Every stdlib subroutine includes a text description as well as
+diagrams of the call and return stack. From `stdio.pvvs` we see the call stack
+for `printf` reproduced below.
+
+ Call Stack:
+ ACSII '\0'
+ string word n
+ ...
+ string word 1
+ substitution n
+ ...
+ substitution 1
+ number of substitutions <-- TOS
+
+The text description for `printf` also informs us that, if we are printing a
+static string (i.e. no substitutions like '%d'), the `number of substitutions`
+should be `0` and it should be immediately followed by `string word 1`. Looking
+at the call stack, that makes sense since we have no substitutions to place
+between those two things.
+
+Note the ASCII `\0` on the call stack. That corresponds to the null terminator
+at the end of our string that was automatically placed by the `A""` syntax.
+
+Don't forget to `#include` the relevant stdlib files. This is done at the
+bottom of the file since VVhitespace files are executed from top to bottom. You
+wouldn't want to accidentally start executing random library code!
+
+Putting all that together, we discover a greatly simplified program.
+
+ A"Hello, world!\n"
+ SSSSN | PUSH 0 (number of substitutions)
+ NSTTSSSN | JSR > 1000 (stdlib:printf)
+ NNN | Terminate program
+ #include <stdio.pvvs>
+
+This is already saved in `hello.pvvs` which you can execute with `make run`.