This repository contains supplementary material related to the paper

Foundational Extensible Corecursion
Jasmin Christian Blanchette, Andrei Popescu, and Dmitriy Traytel

The archive corec.tgz provides the Isabelle formalization of the

1. examples from Section 2 and Hinze and James [28]
2. metatheory from Section 3
3. prototype package from Section 4

The formalization has been processed with Isabelle2014 which is available here:

http://isabelle.in.tum.de/website-Isabelle2014

1. Examples

All definitions and proofs from Section 2 as well as all examples from Hinze and James [28] have been formalized and can be browsed in both pdf (stream_examples.pdf, tree_examples.pdf, llist_examples.pdf and ufp_examples.pdf) and html (html/Corec/index.html) formats. The raw Isabelle sources which were used to generate this pdf and html output are contained in the following folders:

src/Stream_User
src/Tree_User
src/Binary_Tree_User
src/LList_User

To ease the experimentation we also provide a Haskell file (Examples.hs) containing many examples (operating on plain Haskell lists rather than streams).

2. Metatheory

The metatheory from Section 3 has been formalized for an arbitrary axiomatized functor F (more precisely bounded natural functor). Only html (html/Corec/index.html) is available for browsing the formalization here. The raw Isabelle sources which were used to generate this html output are contained in the src/Metatheory folder.

3. Prototype package

The rudimentary automation that we sketch in Section 4 consists of two shell scripts

src/Metatheory/corecupto_init.sh <name> <editor>
src/Metatheory/corecupto_step.sh <name> <editor>

which are used to initialize the corecursion state and to make a step (i.e. register a new well-behaved operation) based on the previous corecursion state, respectively. The scripts copy the metatheory theories to the folder , rename the theory files and constants in the files according to the current step number and open the files that the user is supposed to adjust (replacing the axiomatization with the concrete functor/operation of interest) with the given .

The scripts were used to register the example functions on streams and trees as well-behaved. The output of the scripts can be found in src/Stream, src/Tree, src/LList, and src/Binary_Tree; where only the theory files with "Input" in their names have been further edited manually. This output was itself used to define the examples from Section 2.