projects / vvhitespace / blame
| Commit | Line | Data |
|---|---|---|
| 048de9cc AT |
1 | # Overview # |
| 2 | ||
| 3 | This example starts with the `Hello, world!` example from Wikipedia's | |
| 4 | Whitespace page, gradually rewriting it to use the ASCII string feature of the | |
| 5 | VVhitespace compiler and the `printf` subroutine from the stdlib. | |
| 6 | ||
| b3a0b302 | 7 | # Code Commentary # |
| 048de9cc AT |
8 | |
| 9 | Wikipedia's `Hello, World!` example is reproduced below. It follows a simple | |
| 10 | form, pushing an integer corresponding to an ASCII character onto the stack and | |
| 11 | then printing it with an IO instruction, repeating this two part process for | |
| 12 | each character before terminating with the final instruction. | |
| 13 | ||
| 14 | SSSTSSTSSSN | Push +72 (ASCII H) | |
| 15 | TNSS | Output character | |
| 16 | SSSTTSSTSTN | Push +101 (ASCII e) | |
| 17 | TNSS | Output character | |
| 18 | SSSTTSTTSSN | Push +108 (ASCII l) | |
| 19 | TNSS | Output character | |
| 20 | SSSTTSTTSSN | Push +108 (ASCII l) | |
| 21 | TNSS | Output character | |
| 22 | SSSTTSTTTTN | Push +111 (ASCII o) | |
| 23 | TNSS | Output character | |
| 24 | SSSTSTTSSN | Push +44 (ASCII ,) | |
| 25 | TNSS | Output character | |
| 26 | SSSTSSSSSN | Push +32 (ASCII space) | |
| 27 | TNSS | Output character | |
| 28 | SSSTTTSTTTN | Push +119 (ASCII w) | |
| 29 | TNSS | Output character | |
| 30 | SSSTTSTTTTN | Push +111 (ASCII o) | |
| 31 | TNSS | Output character | |
| 32 | SSSTTTSSTSN | Push +114 (ASCII r) | |
| 33 | TNSS | Output character | |
| 34 | SSSTTSTTSSN | Push +108 (ASCII l) | |
| 35 | TNSS | Output character | |
| 36 | SSSTTSSTSSN | Push +100 (ASCII d) | |
| 37 | TNSS | Output character | |
| 38 | SSSTSSSSTN | Push +33 (ASCII !) | |
| 39 | TNSS | Output character | |
| 40 | SSSTSTSN | Push +10 (ASCII '\n') | |
| 41 | TNSS | Output character | |
| 42 | NNN | Terminate program | |
| 43 | ||
| 44 | If we push the string onto the stack in reverse order we can rearrange the | |
| 45 | code as shown below. Now we're first pushing all the ASCII characters onto the | |
| 46 | stack, then printing them all at once. | |
| 47 | ||
| 48 | SSSTSTSN | Push +10 (ASCII '\n') | |
| 49 | SSSTSSSSTN | Push +33 (ASCII !) | |
| 50 | SSSTTSSTSSN | Push +100 (ASCII d) | |
| 51 | SSSTTSTTSSN | Push +108 (ASCII l) | |
| 52 | SSSTTTSSTSN | Push +114 (ASCII r) | |
| 53 | SSSTTSTTTTN | Push +111 (ASCII o) | |
| 54 | SSSTTTSTTTN | Push +119 (ASCII w) | |
| 55 | SSSTSSSSSN | Push +32 (ASCII space) | |
| 56 | SSSTSTTSSN | Push +44 (ASCII ,) | |
| 57 | SSSTTSTTTTN | Push +111 (ASCII o) | |
| 58 | SSSTTSTTSSN | Push +108 (ASCII l) | |
| 59 | SSSTTSTTSSN | Push +108 (ASCII l) | |
| 60 | SSSTTSSTSTN | Push +101 (ASCII e) | |
| 61 | SSSTSSTSSSN | Push +72 (ASCII H) | |
| 62 | TNSS | Output character | |
| 63 | TNSS | Output character | |
| 64 | TNSS | Output character | |
| 65 | TNSS | Output character | |
| 66 | TNSS | Output character | |
| 67 | TNSS | Output character | |
| 68 | TNSS | Output character | |
| 69 | TNSS | Output character | |
| 70 | TNSS | Output character | |
| 71 | TNSS | Output character | |
| 72 | TNSS | Output character | |
| 73 | TNSS | Output character | |
| 74 | TNSS | Output character | |
| 75 | TNSS | Output character | |
| 76 | NNN | Terminate program | |
| 77 | ||
| 78 | As a convenience, the VVhitespace compiler will accept `A""` syntax, generating | |
| 79 | a sequence of `PUSH` instructions, just like the prior examples, that places a | |
| 80 | null-terminated ASCII string on the stack. This allows us to shorten the | |
| 81 | program. Like before, the start of the string is closest to the top of the | |
| 82 | stack. Unlike before, there is now a null terminator at the end of the string. | |
| 83 | For now, we'll just leave that on the stack when the program terminates. | |
| 84 | ||
| 85 | A"Hello, world!\n" | |
| 86 | TNSS | Output character | |
| 87 | TNSS | Output character | |
| 88 | TNSS | Output character | |
| 89 | TNSS | Output character | |
| 90 | TNSS | Output character | |
| 91 | TNSS | Output character | |
| 92 | TNSS | Output character | |
| 93 | TNSS | Output character | |
| 94 | TNSS | Output character | |
| 95 | TNSS | Output character | |
| 96 | TNSS | Output character | |
| 97 | TNSS | Output character | |
| 98 | TNSS | Output character | |
| 99 | TNSS | Output character | |
| 100 | NNN | Terminate program | |
| 101 | ||
| 102 | Finally, we will use `printf` from the stdlib to shorten that mass of IO | |
| 103 | instructions. Every stdlib subroutine includes a text description as well as | |
| 104 | diagrams of the call and return stack. From `stdio.pvvs` we see the call stack | |
| 105 | for `printf` reproduced below. | |
| 106 | ||
| 107 | Call Stack: | |
| 108 | ACSII '\0' | |
| 109 | string word n | |
| 110 | ... | |
| 111 | string word 1 | |
| 112 | substitution n | |
| 113 | ... | |
| 114 | substitution 1 | |
| 115 | number of substitutions <-- TOS | |
| 116 | ||
| 117 | The text description for `printf` also informs us that, if we are printing a | |
| 118 | static string (i.e. no substitutions like '%d'), the `number of substitutions` | |
| 119 | should be `0` and it should be immediately followed by `string word 1`. Looking | |
| 120 | at the call stack, that makes sense since we have no substitutions to place | |
| 121 | between those two things. | |
| 122 | ||
| 123 | Note the ASCII `\0` on the call stack. That corresponds to the null terminator | |
| 124 | at the end of our string that was automatically placed by the `A""` syntax. | |
| 125 | ||
| 126 | Don't forget to `#include` the relevant stdlib files. This is done at the | |
| 127 | bottom of the file since VVhitespace files are executed from top to bottom. You | |
| 128 | wouldn't want to accidentally start executing random library code! | |
| 129 | ||
| 130 | Putting all that together, we discover a greatly simplified program. | |
| 131 | ||
| 132 | A"Hello, world!\n" | |
| 133 | SSSSN | PUSH 0 (number of substitutions) | |
| 134 | NSTTSSSN | JSR > 1000 (stdlib:printf) | |
| 135 | NNN | Terminate program | |
| 136 | #include <stdio.pvvs> | |
| 137 | ||
| 138 | This is already saved in `hello.pvvs` which you can execute with `make run`. |