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Remko Tronçon 2019-11-08 22:47:01 +01:00
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@ -4,12 +4,11 @@ WAForth is a bootstrapping Forth interpreter and dynamic compiler for
[WebAssembly](https://webassembly.org). You can see it in a demo [WebAssembly](https://webassembly.org). You can see it in a demo
[here](https://el-tramo.be/waforth/). [here](https://el-tramo.be/waforth/).
It is (almost) entirely written in WebAssembly and Forth, and the compiler It is entirely written in (raw) WebAssembly, and the compiler
generates WebAssembly code on the fly. The only parts for which it relies on generates WebAssembly code on the fly. The only parts for which it relies on
external (JavaScript) code is the dynamic loader (since WebAssembly [doesn't external (JavaScript) code is to dynamically load modules (since WebAssembly [doesn't
support JIT support JIT yet](https://webassembly.org/docs/future-features/#platform-independent-just-in-time-jit-compilation)),
yet](https://webassembly.org/docs/future-features/#platform-independent-just-in-time-jit-compilation)), and the I/O primitives to read and write a character to a screen.
and the I/O primitives to read and write a character.
Parts of the implementation were influenced by Parts of the implementation were influenced by
[jonesforth](http://git.annexia.org/?p=jonesforth.git;a=summary). [jonesforth](http://git.annexia.org/?p=jonesforth.git;a=summary).
@ -22,12 +21,12 @@ core word tests.
## Install Dependencies ## Install Dependencies
The build uses [Racket](https://racket-lang.org) for processing the WebAssembly The build uses the [WebAssembly Binary
code, the [WebAssembly Binary Toolkit](https://github.com/WebAssembly/wabt) for Toolkit](https://github.com/WebAssembly/wabt) for converting raw WebAssembly
converting it in binary format,and [Yarn](https://yarnpkg.com) for managing the text format into the binary format, and [Yarn](https://yarnpkg.com) for
dependencies of the shell. managing the dependencies of the shell.
brew install wabt yarn minimal-racket brew install wabt yarn
yarn yarn
@ -60,7 +59,7 @@ format](https://webassembly.github.io/spec/core/text/index.html). The text
format isn't really meant for writing code in, so it has no facilities like a format isn't really meant for writing code in, so it has no facilities like a
real assembler (e.g. constant definitions, macro expansion, ...). real assembler (e.g. constant definitions, macro expansion, ...).
To help with maintenance, the WebAssembly file is piped through a simple string To help with maintenance, the WebAssembly file is piped through a simple string
preprocessor that replaces constants with defined values. preprocessing script that replaces constants with defined values.
### The Interpreter ### The Interpreter
@ -88,7 +87,7 @@ the next offset, which in turn is recorded in the word dictionary.
Because words reside in different modules, all calls to and from the words need Because words reside in different modules, all calls to and from the words need
to happen as indirect `call_indirect` calls through the shared function table. to happen as indirect `call_indirect` calls through the shared function table.
This of course introduces some overhead, although it seems limited. This of course introduces some overhead, although it appears limited.
As WebAssembly doesn't support unstructured jumps, control flow words As WebAssembly doesn't support unstructured jumps, control flow words
(`IF/ELSE/THEN`, `LOOP`, `REPEAT`, ...) can't be implemented in terms of more (`IF/ELSE/THEN`, `LOOP`, `REPEAT`, ...) can't be implemented in terms of more