pltools / ocanren

Statically typed embedding of miniKanren relational programming language into OCaml

OCanren is a strongly-typed embedding of relational programming language miniKanren into OCaml. Nowadays, the implementation of OCanren strongly reminds faster-miniKanren. Previous implementation was based on microKanren with disequality constraints.

See installation instructions, API documentation for more details, or ReadTheDocs for detailed information. (All papers about OCanren are not located in the separate repo.)

Check our template repository for OCanren projects for faster startup!

Installation

To try out developer version of OCanren and OCanren-ppx both, use

  opam pin add https://github.com/PLTools/OCanren.git --yes

OCanren is available in the main OPAM repository, but it's version may be lagging behind.

  opam install OCanren-ppx OCanren --yes

ocanren's Issues

@YueLiPicasso tutorial

• It feels like the wrong type (In tutorial / in OCanren)

• And what is the project and where should it come from (here, here and here) By the way, I couldn't run the example. Is it even correct?

• From time to time I encounter unification of both (==) and (===). What is it correct? There is only one option in the first chapter of the tutorial.

• I didn't find this type in Logic.mli.

Unused variable self warning when using ppx_distrib

When trying to use ppx_distrib on a type with no parameters, warning 27 [unused-var-strict] is emitted:

3 | [%%distrib
4 | type nonrec t = 
5 |   | Integer 
6 |   | Boolean
7 | [@@deriving gt ~options:{ show; fmt; gmap }]
8 | 
9 | type ground = t ]
Error (warning 27 [unused-var-strict]): unused variable self.

wrong type signature for distrib from Fmap2

For two argument type constructors, the distrib function shall have type:

(('a,'b) injected, ('c, 'd) injected) T.t -> (('a, 'c) t, ('b, 'd) T.t) injected

instead of the wrong one as appear in the source.

Integrate @YueLiPicasso's tutorial

List of subtasks copy-pasted from YueLiPicasso/OCanrenTutorial#2

Group S: Problems that have straightforward fix or cause disputes on trivial matters (S for straight)

• spell errors
• text formatting (such as adding newlines and indentation)
• removal of double semi-colons ( ;; ) at end of OCaml code lines
• Alternative commands for the install/uninstall of OCanren.
• Write in infix or prefix style, for infix operators ?
• change of jargon: groundi -> injected
• two versions of build system
• favor of explict lambda abstraction in function definition

Group M: Moderate technical clarifications (M for moderate)

• How to briefly introduce GT? Shall we say that "it provides a Haskell type class style feature to OCaml" or we could say something better?
• Clarify that we do not allow infinite programs, but the programs we write may be viewed as being infinite in theory.
• Description of simple concepts like "stream" in complex/advanced ways could be kept, but a more intuitive explanation can also be added.
• The term "zip" has many meanings, but that adopted in the tutorial is clarified by an example. A deterministic and implementation oriented definition of zipping is good to be added.
• GT.string vs. string to be clarified
• The notion of guarded type may be not useful for some people, but I found it illuminating, so I choose to keep it.
• When does a ground type coincide with its corresponding (fully) abstract type? This may worth some more discussion.
• The comments on the use of -rectypes compiler option serve to explain why we need that flag.
• Explain the two type parameters of the "injected" type constructor could be added.
• Clarify that there are a few syntaxes for OCanren and we are using one of them.

Group P: Philosophical questions

• Shall the author focus the tutorial on the major implementation technique of OCanren and the ideas
  of relational programming, which he is better at, or he should do what he is not good at and update the tutorial very often to explain how to install the latest version of OCanren where there is no fundamental change in its concepts and implementation?