mirror of
https://github.com/russolsen/sallyforth
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108 lines
2.3 KiB
Markdown
108 lines
2.3 KiB
Markdown
# SallyForth: A simple Forth-like language implemented in Python.
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SallyForth is a simple hobby implementation of a FORTH-like programming
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language. Possibly the most interesting thing about SallyForth is the
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name, which
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[Michael Nygard suggested](https://twitter.com/mtnygard/status/1249781530219642883)
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as a name for a FORTH implementation
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at exactly the same time that I happened to be writing this code.
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## Running SallyForth
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SallyForth is writting in Python 3 and will happily run with
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either the standard C Python implementation or Pypy. To
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run SallyForth just kick off the sallyforth.py file:
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````
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$ python sallyforth/sallyforth.py
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````
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## The Sally Language
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Like FORTH, Sally is a stack oriented concatenative programming language.
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What this means is that any constant value in a sallyforth program,
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like a number or a string:
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```
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sallySh> "Hello, world!"
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```
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Has the effect of pushing the value onto an ever present data stack.
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There are also commands or functions -- called *words* -- that you
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can use to do things.
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So the word `p` will pop the value off of the top of the stack
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and print it:
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```
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sallySh> "Hello, world!"
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sallySh> p
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Hello, world!
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```
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Sally parsing is about as simple as you can get: words and constant
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values are separated by whitespace. So if you wanted to print
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a number of values, you could do this:
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```
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sallySh> 1 2 3 p p p
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3
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2
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1
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```
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The only execeptions to the _separated by whitespace rule_ are
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double quoted strings, which work about the way you would expect:
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```
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sallySh> "I can have spaces in my string"
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sallySh> p
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I can have spaces in my string
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```
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Sally comes prepackaged with a host of useful words, everything
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from basic arithmetic:
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```
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sallySh> 1 2 + p
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3
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sallySh> 10 10 * 1 + p
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101
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```
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To boolean logic:
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```
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sallySh> true false and p
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False
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sallySh> false true or p
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True
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```
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To IO:
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```
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sallySh> "hello.txt" read-file
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sallySh> p
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This is the contents of hello.txt.
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Use it wisely.
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```
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You can also define your own words. A word defintion starts with
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a colon, followed by the name of your new word, followed by
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the contents of your new word, enclosed in braces.
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Keep in mind that everything -- including the colon and the braces --
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needs to be set off with whitespace:
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```
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: hello-world { "Hello, world!" p }
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```
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Once your new word is defined you can use it like any other word:
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```
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sallySh> hello-world
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Hello, world!
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```
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