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a simple functional language implementing a generalized exception-like control flow mechanism

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Functional Jump

This is an example implementation of a simple pure ML-like functional language with a non-standard control flow mechanism, which we can call functional jump for now.

It is a simple generalized control flow mechanism for implementing both iteration and branching. Roughly speaking, it tries to unify the following concepts:

  • pattern matching
  • ad-hoc exception introduction and handling
  • goto (yay! the considered-harmful one!)
  • related to continuations

Example

A function computing the sum of the first n integers:

let sum = fun n ->
  >> (n, 0) where
  | (0, acc) -> acc
  | (k, acc) -> >> (k-1, acc+k)
  end

Goals

Potentially, this mechanism can be useful for simplifying recursive function definitions that describe iterations, but involve complicated logic or order of execution that is painful to express in a clear way with normal recursion.

It provides seamless integration of finite-automaton-like control flow into a functional language. Kinda wondering if there is any relation to co-induction or any other fancy topics.

It seems that the correctness of labels and jumps can be statically type-checked, but I haven't proved it yet.

How to build and run

You have to install ocaml compiler and menhir parser generator. It is recommended to use OCaml package manager opam to install menhir.

make
./jump < test/sum.jump

In addition, the file "jump.vim" provides some basic syntax highlighting for Vim text editor. (Please follow/search for the official Vim instructions for installing such syntax files.)

Status

  • Practically no error reporting.
  • No documentation about this control flow mechanism.

References

  1. Edsger Dijkstra (March 1968). "Go To Statement Considered Harmful". Communications of the ACM 11 (3): 147–148.

License

The software is distributed under the conditions of the BSD 3-clause license.

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