95 lines
3.9 KiB
Markdown
95 lines
3.9 KiB
Markdown
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---
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title: "How to be an Irredeemable Nerd and Look Good Doing It"
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date: 2020-11-06
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description: ""
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---
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In a [previous post](/posts/c), I talked a bit about my endeavour to build
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myself a lil' Lisp: PebbLisp. It's a project I work off and on depending on my
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motivation. Recently, I was pretty bored with it, and found myself looking for
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a new project. Having read a bit about Forth, I thought it wouldn't be too hard
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to try implementing it. Plus, this would be a great opportunity do some
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practice with Rust.
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If you're not familiar with Forth, it's a weird little interpreted language
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built around a stack. Passing in a number will add it to the top of the stack,
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passing in a function will (usually) do something with numbers on the stack.
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For example, what happens when you run the following?
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2 3 + .
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First, `2` and `3` are added to the stack. Then, `+` pops the top two items off
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the stack, and adds them. Then it pushes the result back onto the stack.
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Finally, the `.` pops the top item off of the stack, and prints it out:
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5
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You can also compile functions that add some of these elements, and the
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language can become surprisingly expressive:
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: feet 12 * ;
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: yards feet 3 * ;
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5 feet .
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\ This prints 60 (5 feet in inches)
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8 yards .
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\ This prints 288 (6 yards in inches)
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5 yards 2 feet + .
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\ This prints 204 (5 yards + 2 feet)
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So, I figured "hey, looks simple enough", and got to work. Got basic parsing
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going, got the stack pretty functional, added a few functions, whoo. Rust
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turned out to be a great choice. Expressive, safe, and with built-in testing.
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Good stuff. Almost too good. I'd started looking at PebbLisp again. Could I
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write an interpreted language using my own interpreted language? Forth is
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pretty simple, conceptually. How hard could it be?
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Actually, it hasn't been the unholy mess that I was expecting. Yes, my PebbLisp
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is severely lacking (there was no way to take user input before?). No, it has
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nothing anything even remotely resembling a formal language definition (I've
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operated on the "this seems to make sense" principle). With some tweaks though,
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it has kind of worked!
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My to-be-named Forth (Forbble? PLForth? PebForListhble?) is <em>incredibly</em>
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buggy, and pretty tedious even when it does work, but it sort of kind of does!
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$ "feet" 12 * "END"
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$ "yards" 36 * "END"
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5 "yards" 2 "feet" +
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.
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\ This prints 204
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So, for reasons I've yet to suss out:
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* Functions can't be defined using other functions
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* Functions need to be defined using quotes, for goofy string/symbol reasons in PebbLisp.
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* Statements that use a user-defined function seem to ignore the dot operator at the end.
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_Please ignore the awful END symbol it should be easy to fix._
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Anyway, it's been pretty neat to actually try doing something with PebbLisp.
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I've cleaned up a bunch of hacky ways of doing things, and added a few more.
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Some of it is super useful outside of Forbble (Flisbble? Porlth?) too. Since I
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added an `eval` function, and a way to take input, it's actually super easy to
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write up a REPL in PebbLisp itself. Very fun!
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PebbLisp was never intended to be a terrifically practical language. Have I
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mentioned it was originally created to be written and run on a smartwatch?
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Yeah, the Pebble (hence the name). Enjoy typing on its four buttons. This is
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also the reason PebbLisp is written in C, as nothing else worked with their
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SDK. Nonetheless, it is incredibly satisfying to get your own language running
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something even remotely real. Even if that something is another, even less
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useful language.
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I love it.
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If you, like me, enjoy programming enough to do it in your free time, try
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writing a little lang. Forth is a great place to start, and Rust is a great
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language to write in, but there are certainly others that would be cool to work
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with. Or just try _using_ a different language. I'm not saying your
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Forth knowledge will get you hired anywhere, but it's a good excuse to look at
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your code differently, which is always a good idea.
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