Computer

Experimental fork of Marelle to create a simple shell hack as a front-end for a distributed peer-to-peer search engine using Prolog..

Computer uses logic programming to describe search terms, contexts, and rules to provide a recursive search mechanism. Prolog's built-in unification and search mechanisms makes writing and using Web search terms and their dependencies elegant. Anecdotally, writing search terms for Computer has the feel of teaching it about types, rather than the feel of writing a list of searches one does on any given centralized search engine today.

Current status

Experimental but working.

Features

Computer has a few features

• Checking and meeting dependencies (preconditions)
• Testing whether a search term has already been discerned (post-conditions)
• Ability to specify context-dependent search.

It also has some interesting differences:

• Can write checks (trusts predicates) without needing to say how to meet them (discern predicates)
• The dependencies of a search term can vary by context.
• Succinct definition of new types of search terms using logical rules

Installing 'computer'

Quickstart

Pick a bootstrap script from the options below. If you're not sure, choose the stable version.

Version	Bootstrap command
master (dev)	bash -c "$(curl -fsSL https://raw.githubusercontent.com/monadicus/computer/master/bootstrap.sh)"

This will install computer for all users, putting the executable in /usr/local/bin/computer.

Manual version

1. Get Prolog
   • On OS X, with Homebrew: brew install swi-prolog
   • On Ubuntu, with apt-get: sudo apt-get install swi-prolog-nox
   • On FreeBSD, with pkgng: sudo pkg install swi-pl
2. Get git
   • On OS X, with Homebrew: brew install git
   • On Ubuntu, with apt-get: sudo apt-get install git
   • On FreeBSD, with pkgng: sudo pkg install git
3. Clone and set up computer

# clone the repo
mkdir -p ~/.computer
git clone https://github.com/monadicus/computer ~/.computer/computer

# set up an executable in ~/.computer/bin
mkdir -p ~/.computer/bin
cat >~/.computer/bin/computer <<EOF
#!/bin/sh
exec swipl -q -t main -s ~/.computer/computer/computer.pl "\$@"
EOF
chmod a+x ~/.computer/bin/computer

# add ~/.computer/bin to your PATH
# (the exact commands depend on the shell you use)
echo 'export PATH=~/.computer/bin:$PATH' >>~/.profile
source ~/.profile

Writing deps

Make a computer-deps/ folder inside your project repo. Each package has two components, a met/2 goal which checks if the dependency is met, and an meet/2 goal with instructions on how to actually meet it if it's missing.

For example, suppose I want to write a dep for Python that works on recent Ubuntu flavours. I might write:

% python is a target to meet
pkg(python).

% it's installed if it exists at /usr/bin/python
met(python, linux(_)) :- exists_file('/usr/bin/python').

% we can install by running apt-get in shell
meet(python, linux(_)) :-
    % could also use: install_apt('python-dev')
    sh('sudo apt-get install -y python-dev').

To install python on a machine, I'd now run computer meet python.

To install pip, I might write:

pkg(pip).

% pip is installed if we can run it
met(pip, _) :- which(pip).

% on all flavours of linux, try to install the python-pip package
meet(pip, linux(_)) :- install_apt('python-pip').

% on all platforms, pip depends on python
depends(pip, _, [python]).

Note our our use of platform specifiers and the _ wildcard in their place. To see your current platform as described by computer, run computer platform. Examples include: osx, linux(precise) and linux(raring).

Running deps

See available deps

This runs every met/2 statement that's valid for your platform.

computer scan

Install something

This will run the meet/2 clause for your package, provided a valid one exists for your current platform.

computer meet python

See your platform

To find the right platform code to use in deps you're writing, run:

computer platform

It reports the code for the platform you're currently on.

Where to put your deps

Like both Babushka and Babashka, Computer looks for deps in ~/.computer/deps and in a folder called computer-deps in the current directory, if either exists. This allows you to set up a personal set of deps for your environment, as well as project-specific deps.

Examples

See computer-deps repo for working examples.

Developing

Run make test to run the test suite.