40 lines
1.9 KiB
Markdown
40 lines
1.9 KiB
Markdown
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# LVTL-X: a compact and fair VTL-2 port to POSIX AWK
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## About
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LVTL-X is a port of the [VTL-2](https://rosettacode.org/wiki/Category:VTL-2) retro programming language interpreter to the POSIX AWK runtime. Unlike the previous effort, LVTL-W, that only worked in BusyBox and GAWK, this version works in any POSIX-compliant environment. On top of that, LVTL-X is extremely compact and takes under 100 SLOC of portable and readable AWK code.
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## Usage
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The easiest way is to run the `./lvtl` shell wrapper, either stand-alone or with a program file path to preload. You can also specify a non-default AWK interpreter to use with the `AWK` environment variable for the wrapper to use.
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Alternatively, you can run the LVTL-X script directly like this:
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```sh
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POSIXLY_CORRECT=1 awk -f lvtl-x.awk -- [/path/to/your/vtl/program.vtl] -
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```
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If running without a wrapper and specifying a program to preload, don't forget to put another `-` after it.
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## Differences from the Altair original
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LVTL-X stands out from other LVTL versions by being closer to the original VTL-2, but still has some important differences that shouldn't be ignored:
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- both LF and CRLF are accepted (but not saved into RAM)
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- only LFs are printed instead of CRLFs
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- maximum line length is not enforced
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- all whitespace after the line number is fully ignored
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- any whitespace within expressions is also insignificant
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- parentheses are NOT auto-closed at the end of the statement
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- only 26 characters (A-Z) are valid generic variable names
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- supports all standard VTL-2 binary operators: +, -, *, /, =, >, <
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- jumps to itself (like 10 #=10) are prohibited and counted as nops
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- no file I/O (only the option to preload VTL code from a file)
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- self-modifying programs won't work correctly
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Nevertheless, any program that's valid on LVTL-X will run on the original VTL-2/02 implementations too.
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## Credits
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Created by Luxferre in 2026, released into the public domain with no warranties.
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