Trealla Prolog

This is a fork of Trealla Prolog for experimenting with WebAssembly/WASI. For more info on Trealla, check out the parent repository.

We endeavor to keep this fork as close as possible to the upstream and contribute all stable changes upstream. Ideally, when Wasm support is better stablized, this fork won't need to exist.

Download

You can find binaries on the Releases page.

Differences from upstream

• library(wasm) JSON-based programmatic toplevel.
• library(wasm_*) host-guest interop.
• library(pseudojson) Very fast JSON parser/generator (but not validator).
• Wasm system predicates: '$host_call'/2 and '$host_resume'/1 (see js_eval/2 in library/wasm_js.pl).

Compile targets

There's a bunch of new compile targets for Wasm.

wasm

make wasm will build a pure WASI version of Trealla: tpl.wasm. This binary can be executed by any runtime that supports WASI. (Mostly) upstreamed.

libtpl

make libtpl will build a Wasm binary with host calls enabled: libtpl.wasm. This adds host-guest interop exports and imports that break pure WASI compatibility. This is currently used by the Go port.

libtpl-js

make libtpl-js builds the trealla-js version of libtpl. Includes JS-specific predicates.

libtpl-spin

You can use Trealla Prolog with Spin, a server-side runtime for WebAssembly.

make libtpl-spin builds the Spin-flavored libtpl.

make SPINDIR=path/to/spin/source wit to generate the Wasm component code via wit-bindgen. These files are included in the repository so you won't need to generate them unless adding support for a new one. Currently requires wit-bindgen v0.2.0.

Spin Components

👉 For a helpful template and README to get started, check out trealla-spin. See also library/spin.pl.

• Inbound HTTP (via http_handler/4 multifile predicate)
• Outbound HTTP (via http_fetch/3)
• Outbound PostgreSQL
• SQLite
• Inbound Redis
• Outbound Redis
• Key-value store

Place a file called init.pl or lib.pl in your root directory of the Spin component. From there you can load other modules, etc. You can also use set the INIT environment variable to a file path to use that file instead.

Example of a visit counter using Spin:

:- use_module(library(spin)).

% Roughly:
% http_handler(verb(Path, QueryParams), Headers, RequestBody, ResponseCode) :-
%	http_header_set("cache-control", "no-cache"),
%   write(http_body, 'response body').

http_handler(get("/", _), _, _, 200) :-
	html_content,
	setup_call_cleanup(
		store_open(default, Store),
		(
			(  store_get(Store, counter, N0)
			-> true
			;  N0 = 0
			),
			succ(N0, N),
			store_set(Store, counter, N)
		),
		store_close(Store)
	),
	format(http_body, "Welcome, visitor #~d!", [N]).

• Trealla Prolog: parent repository
• trealla-js: Trealla for Javascript
• trealla-prolog/go: Trealla for Go