What is this?

This is a program synthesizer for well-behaved bidirectional program written in HOBiT (https://doi.org/10.1007/978-3-319-89884-1_2).

You can obtain a bidirectional program from an unidirectional program and input-output examples.

How to Build

Install stack first. Then, type the following command.

stack build

How to use

To synthesize a bidirectional program, you need to specify the spec file that contains the file name of unidirectional programs and backward-behavior examples.

For example, if you want to synthesize bidirectional appendPair, which is the running example in our paper, you need to specify the spec file paper_experiments/List/append/spec.hobit as follows:

stack exec synbit paper_experiments/List/append/spec.hobit

After running the command, bidirectional appendPair that meets backward behaciors written in paper_experiments/List/append/examples.hobit will be shown.

Benchmarks

Run stack bench --benchmark-arguments "PATH_TO_SPEC_FILE", where the part PATH_TO_SPEC_FILE is supposed to be related with the path to a spec.hobit in the paper_experiments directory. For example, to benchmark the append example, run:

stack bench --benchmark-arguments "paper_experiments/List/append/spec.hobit"

We used the criterion package (https://hackage.haskell.org/package/criterion) for benchmarks.

About HOBiT (Reprint)

A prototype implementation of a higher-order bidirectional programming language HOBiT.

How to Use

Just run hobit. Then, one will see the following prompt of HOBiT's read-eval-print loop.

HOBiT>

You can type expressions to evaluate.

HOBiT> 1 + 2
3

The read-eval-print loop also accepts some commands, where valid commands are displayed by typing :h.

HOBiT> :h
:quit
    Quit REPL.
:load FILEPATH
    Load a program.
:reload
    Reload the last program.
:put EXP [EXP [EXP]]
    Evaluate a function as "put".
:get Exp [Exp]
    Evaluate a function as "get".
:set verbosity INT
    Set verbosity to the specified number.
:help
    Show this help.
:type EXP
    Show expression's type.

The ":get" and ":put" are most interesting parts of HOBiT's functionality. To explain the behavior, we first load the file ./example/Unlines.hobit.

 HOBiT> :l examples/Unlines.hobit
 ...
 unlinesB :: BX [[Char]] -> BX [[Char]]
 ...

The type constructor "BX" indicates that the values can be updated. To run the unlinesB function forward, just use the :get command.

 HOBiT> :get unlinesB ["a", "b", "c"]
 "a\nb\nc\n"

The command :put is used to invoke the backward execution of unlinesB.

 HOBiT> :put unlinesB ["a", "b", "c"] "AA\nBB\nCC\n"
 ...
 ["AA","BB","CC"]
 HOBiT> :put unlinesB ["a", "b", "c"] "AA\nBB\n"
 ...
 ["AA","BB"]
 HOBiT> :put unlinesB ["a", "b", "c"] "AA\nBB\nCC\nDD\n"
 ...
 ["AA","BB","CC","DD"]

The directory examples contains several examples. Enjoy!

Differences from the Paper

where clauses are not implemented.
Some arithmetic operators are not implemented (such as /=, <, *...).
Bidirectional case expressions and let expressions are case* and let*.
We do not provide direct ways to write bidirectional constructors. Instead, we adopt the syntactic notion called the bidirectional context, under which constructors are turned into bidirectional ones automatically.
- There are three forms of expressions that open bidirectional contexts: (1) let*, case* (except exit-conditions and reconcilers), and constructors in bidirectional contexts.
- Bidirectional contexts are explicitly opened by (| and |).
- The bidirectional context is shallow in the sense that arguments of functions are unaffected. For example, [] in (| f [] |) is not promoted.

Note

The executable creates the file named .HOBiT_history in the home directory.

If the error gcc' failed in phase Linker'. (Exit code: 1) is showen, sudo apt install libtinfo-dev may resolve it.

kztk-m/synbit