-# 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`.
projects / vvhitespace / blobdiff