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https://github.com/lambduli/minilog
A small logic programming language.
https://github.com/lambduli/minilog
language logic-programming programming-language prolog prolog-implementation repl unification
Last synced: 3 months ago
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A small logic programming language.
- Host: GitHub
- URL: https://github.com/lambduli/minilog
- Owner: lambduli
- License: mit
- Created: 2022-12-01T08:15:22.000Z (almost 2 years ago)
- Default Branch: main
- Last Pushed: 2024-05-14T10:44:46.000Z (6 months ago)
- Last Synced: 2024-05-14T11:49:33.267Z (6 months ago)
- Topics: language, logic-programming, programming-language, prolog, prolog-implementation, repl, unification
- Language: Haskell
- Homepage:
- Size: 89.8 KB
- Stars: 17
- Watchers: 2
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
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README
# Minilog
Minilog is a very small programming language implementation.
It's goal is to capture the essence of logic programming.
> For the implementation write up see: [the write up](./WRITEUP.md).
It is very much a subset of Prolog, at least in terms of the syntax.
The biggest (intended) difference in terms of a runtime behaviour is the strict
`occurs` checking.
Unlike Prolog, Minilog does not accept infinite terms.
This means that the following snippet will succeed in Prolog but not in Minilog:
```prolog
X = foo(X).
```
## Syntax
As stated above, Minilog's syntax is a subset of the syntax of Prolog.
In Minilog you have:
- Atoms
`foo`, `z`
- Variables
`X`, `Y`
- Wildcards
`_`
- Structs
`foo(X, thing)`
- Facts
`plus(z, N, N).`
- Rules
`plus(s(N), M, s(R)) :- plus(N, M, R).`
- Conjunctions
`times(N, M, R), plus(R, M, A).`
- Unification Operator
`X = something`
----
Here is an example of a valid Minilog knowledge base definition:
```prolog
plus(z, N, N).
plus(s(N), M, s(R)) :- plus(N, M, R).
times(z, _, z).
times(s(N), M, A) :- times(N, M, R), plus(R, M, A).
fact(z, s(z)).
fact(s(N), R) :- fact(N, PR), times(s(N), PR, R).
```
And here is an example of a valid query:
```prolog
?- fact(A, B) , plus(A,B, s(s(z))) .
```
---
## What is not in Minilog?
- numbers
- arithmetics (obviously)
- strings
- explicit or (`;`)
- cuts (`!`)
## What is it for?
The implementation is just a complement of the [write up](./WRITEUP.md).
The goal of this project is to offer an introductory level almost tutorial-like description of an implementation of a simple abstract machine for a logic language.
The design of the implementation is not aming to represent a practical implementation of a logic programming language.
It should not be considered more than an initial exposition to the ideas behind concepts like
unification, proof search that happens during the evaluation and a backtracking in such a proof search.
You could also say that the design of the implementation was chosen to be observable by default. Indeed, as the runtime is implemented
as a simple "stepping" interpreter, we can very much see "inside" the process.
The write up goes into more detail on that topic.
The goal of the project is not to be a rigorous introduction into the matter! At best it should serve as a toy-like demonstration; similar to when a math or physics teacher reaches for a vast (but still valid) simplification to make some complicated sounding concept more approachable.
## How can you use it?
1) You run `cabal build` and if that succeeded `cabal run`.
2) You can use the knowledge base in the repository, modify it, or use your own. It is loaded into the repl using a command `:load ` like `:load factorial.pl`.
3) You write Prolog-like query and hit enter.
4) When presented with a result, you either write `:next` and hit enter (to backtrack) or you write `:done` and hit enter to conclude the computation.
5) When you want to quit the REPL, you submit `:q` or `:Q`.