# `wrapper`

This is a prototype tool to help port a plain Prolog application to Logtalk. It can also be used to enable applying other Logtalk developer tools, such as the documenting and diagramming tools, to plain Prolog code.

The tool takes a directory of Prolog files or a list of Prolog files, loads and wraps the code in each file using an object wrapper, and advises on missing directives to be added to those objects by using the compiler lint checker and the reflection API. The user can then either save the generated wrapper objects or copy and paste the printed advice into the Prolog files (updating them to Logtalk files by adding the object opening and closing directives to the Prolog files). The wrapper objects use `include/1` directives to include the Prolog files and can be loaded for testing and for use with other tools. The wrapped Prolog files are not modified and thus require only read permission.

## API documentation

This tool API documentation is available at:

../../apis/library_index.html#wrapper

## Loading

This tool can be loaded using the query:

    | ?- logtalk_load(wrapper(loader)).

## Workflows

The typical porting workflow is:

    | ?- wrapper::rdirectory(root_directory_of_prolog_code).
    ...
    | ?- wrapper::save.
    ...

See the next section on how to customize the API calls for more flexible processing.

## Customization

The tool can be customized by extending the `wrapper` object. A common scenario is when wrapping plain Prolog code just to take advantage, for example, of the documenting tool or for generating cross-referencing diagrams. In this case, we can workaround any compiler errors by specializing the inherited definitions for the `term_expansion/2` and `goal_expansion/2` predicates and then load the wrapper objects for further processing by using the `include_wrapped_files(false)` option described below.

The API predicates also accept a set of options for customization:

- `prolog_extensions(Extensions)`
  list of file name extensions used to recognize Prolog source files (default is `['.pl', '.pro', '.prolog']`)
- `logtalk_extension(Extension)`
  Logtalk file name extension to be used for the generated wrapper files (default is `'.lgt'`)
- `exclude_files(Files)`
  list of Prolog source files to exclude (default is `[]`)
- `exclude_directories(Directories)`
  list of sub-directories to exclude (default is `[]`)
- `include_wrapped_files(Boolean)`
  generate `include/1` directives for the wrapped Prolog source files (default is `true`)

The use, by default, of `include/1` directives to wrap the code in Prolog source files facilitates running in parallel the Logtalk port and the original Prolog code. This is specially useful when the Prolog code being ported lacks a comprehensive set of tests that could be adapted to verify the Logtalk port. The generated Logtalk files can also take advantage of `uses/2` directives, including predicate aliases and predicate shorthands to minimize the changes to the original Prolog code and help verify if replacement calls to Logtalk library predicates provide the same semantics as the original calls.

## Current limitations

- The tool cannot deal with syntax errors in the Prolog files. These errors usually occur when using a backend Prolog system different from the one used to compile the original plain Prolog code. A common cause of syntax errors is operator definitions. These can often be solved by defining those operators for the Prolog backend used to run Logtalk and this tool. An alternative is to preload the Prolog files where those operators are declared. Preloading the plain Prolog application can also help in wrapping it by ensuring that its dependencies are also loaded.

- The tool assumes that all files to be wrapped have different names (even if found in different directories). If that is not the case, the name conflicts must be manually solved before using the tool.

- There’s only preliminary support for dealing with meta-predicates and advise on missing meta-predicate directives.