package tezos-lwt-result-stdlib

Lwtreslib: an Lwt- and Result-friendly addition/replacement for the Stdlib

The OCaml's Stdlib modules are orthogonal: each define their own datatype and a set of functions operating on this datatype. Result for result, Option for option, List for list, etc. This orthogonality provides a high expressive power for a low lines-of-code count. E.g.,

let fold f init xs =
   List.fold_left
      (fun acc x -> Result.bind acc (fun acc -> f acc x))
      (Result.ok init)
      xs

However, in code-bases that make heavy uses of some datatypes, a little more integration is welcome. For example, in code bases that use the result type pervasively, the fold function above should be available in a module of list-traversing functions.

Lwtreslib is a library that supplement some of the OCaml's Stdlib modules with a tight integration of Lwt and Result. It focuses on data-structures that can be traversed (iterated, mapped, folded, what have you).

Design principles

1. Exception-safety

   The functions exported by Lwtreslib do not raise exceptions. These functions may return option or result to indicate that some error happened during traversal, and they may propagate result.

   (For convenience, the module WithExceptions provides a few exception-raising functions because they are convenient in specific contexts.)

2. Consistency

   Exported functions and values have consistent names that reflect their consistent semantic.

Reading guide

The sources of Lwtreslib are organised as follow:

• bare/ contains the sources for a bare-bones implementation of Lwtreslib that provides monadic combinators and collection traversals.

  • bare/sigs/ contains the sources for the signatures of all the modules exported by bare/

  • bare/functor_outputs contains the sources for the signatures of all the modules constructed by functors exported by bare/

  • bare/structs contains the sources for of all the modules exported by bare/

• examples/traces/ contains multiple example implementation of traces. A trace is a data-structure that holds multiple errors organised in a way that reflects the way the errors happened. Specifically, errors can be stringed together to represent that the control flow traversed multiple points, or they can be held side-by-side to indicate that they happen in to simultaneously evaluating promises.

  The code in this directory is meant more as examples than fully-fledged traces, but they can also be used for prototyping or as a basis for a more complete trace implementation.

• traced/ contains the sources for a trace-enabled implementation of Lwtreslib that provides monadic combinators and collection traversals. This implementation provides all the functionality of bare/ with added support for traces (i.e., structured collections of errors).

  • traced/sigs/ contains the sources for the signatures of all the modules exported by traced/

  • traced/functor_outputs contains the sources for the signatures of all the modules constructed by functors exported by bare/

  • traced/structs contains the sources for of all the modules exported by bare/. These modules are functorised over the implementation of a trace. The file traced/structs/structs.ml contains an all-in-one functor for instantiating all of the modules.

• test/ contains code to test the library.