Trealla for Spin

This is a collection of Spin templates for using the WebAssembly build of Trealla Prolog.

Currently a work in progress. See here for more info about what's supported.

Usage

Installing/updating

You'll need to install Spin first.

Then, add the templates from this repository to Spin:

spin templates install --git https://github.com/guregu/trealla-spin --update

Start a new project

$ spin new http-prolog
Enter a name for your new application: hello-world
Description: prolog is web scale
HTTP base: /
HTTP path: /...

$ cd hello-world; ls 
spin.toml src

Write some Prolog

The Prolog program in src/init.pl will be consulted automatically. From here, you can use/consult other files. A couple example handlers for HTTP are included.

Here's a minimal example of an HTTP handler that returns a JSON message with the current time.

:- use_module(library(spin)).

http_handler(get("/json", _), _, _, 200) :-
	wall_time(Time),
	% json_content({"time": Time}) works too
	json_content(pairs([string("time")-number(Time)])).

Write to the http_body stream or use one of the *_content predicates to respond.

format(http_body, "Welcome, visitor #<b>~d!</b>", [N]).

http_handler/4

http_handler/4 is a multifile predicate, just make sure to :- use_module(library(spin)) to import it.

%% http_handler(+Spec, +Headers, +Body, -Status).
%
% Spec is a term representing the request method, path, and query parameters.
% For example, a GET request to /foo?id=xyz&a=123 is get("/foo", ["a"-"123","id"-"xyz"]).
% Headers are the request headers.
% Body is the request body.
% Status is the response status code.
http_handler(Spec, Headers, Body, Status) :- ... .

Run it

$ spin up
Serving http://127.0.0.1:3000
Available Routes:
  my-cool-project: http://127.0.0.1:3000 (wildcard)

Deploy it

The easiest way is to use Fermyon Cloud. Note that Fermyon Cloud doesn't support key-value stores yet, so the default visitor counter example won't work.

$ spin deploy

You can also create OCI images, and Fermyon Platform is a self-hosted platform for running Spin.

Spin library

# library(spin)

# response handler
http_handler/4 (+spec,+list,+body,-integer) [multifile]
# request info
current_http_uri/1      (?string)
current_http_method/1   (?string)
current_http_body/1     (?string)
current_http_param/2
current_http_header/2   (?string,?string) # name,value
# response i/o
http_header_set/2       (+string,+string) # name,value
http_body_output/1      (-stream)
html_content/0  # sets mime header
html_content/1          (+string)
text_content/0
text_content/1          (+string)
prolog_content/0
prolog_content/1        (+term)
# key-value store
store_open/1            (-handle)
store_open/2            (+atom,-handle)
store_close/1           (+handle)
store_get/3             (+handle,?term,?term) # key,value
store_exists/2          (+handle,+term) # key
store_keys/2            (+handle,-list) # all keys 
store_set/3             (+handle,+term,+term) # key,value
store_delete/2          (+handle,+term) # key
# outbound http
http_fetch/3    (+string,-body,+options)

What's next?

• Supporting more Spin components like Redis and SQL.
• Considering stealing the HTTP library's syntax from Scryer Prolog
• Porting php (Prolog Home Page) from CGI to Spin components.
• Document the Spin-related predicates