# mlkit-postgresql

Postgresql library for Standard ML / MLKit

This library provides access to the postgresql database from within SML using the libpq API. The functionality is provided through several layers:

• High-level API. Structure PgDb : DB.

• Medium-level API. Structure PgDb.Handle : DB_HANDLE.

• Low-level API. Structure Postgresql : POSTGRESQL.

With the medium-level and low-level APIs, the programmer manages and propagates connection information explicitly, whereas, with the high-level API, a single connection is setup and managed through side-effecting functions.

There are two versions of the PgDb and PgDb.Handle structures, one that treats SQL code as Standard ML strings (available through pgdb.mlb) and one that treats SQL code as MLKit quotations (available through pgdb-quot.mlb), which requires -quot to be passed to mlkit.

Overview of MLB files

• lib/github.com/melsman/mlkit-postgresql/pgdb.mlb:

  • structure PgDb :> DB where type sql = string

• lib/github.com/melsman/mlkit-postgresql/pgdb-quot.mlb:

  • structure PgDb :> DB where type sql = quot

• lib/github.com/melsman/mlkit-postgresql/pgdb-fn.mlb:

  • signature DB
  • signature DB_HANDLE
  • functor PgDbFn : (X : ...) -> DB

• lib/github.com/melsman/mlkit-postgresql/postgresql.mlb:

  • signature POSTGRESQL
  • structure Postgresql :> POSTGRESQL

Assumptions

A working MLKit installation (see https://github.com/melsman/mlkit). Use brew install mlkit on macOS.

Testing

To test the library, first do as follows:

$ cd src
$ make

Notice that, dependent on the architecture, you may need first to set the environment variable MLKIT_INCLUDEDIR to something different than the default value /usr/share/mlkit/include/. For instance, if you use brew under macOS, you should do as follows:

$ cd src
$ MLKIT_INCLUDEDIR=/usr/local/share/mlkit/include/ make

Then, proceed as follows:

$ cd ../test
$ make init
$ make

Notice that it may be necessary to tweak the src/Makefile and the test/Makefile to specify the location of the MLKit compiler binary, the MLKit include files, and the MLKit basis library.

Use of the package

This library is set up to work well with the SML package manager smlpkg. To use the package, in the root of your project directory, execute the command:

$ smlpkg add github.com/melsman/mlkit-postgresql

This command will add a requirement (a line) to the sml.pkg file in your project directory (and create the file, if there is no file sml.pkg already).

To download the library into the directory lib/github.com/melsman/mlkit-postgresql (along with other necessary libraries), execute the command:

$ smlpkg sync

You can now reference the mlb-file using relative paths from within your project's mlb-files.

Notice that you can choose either to treat the downloaded package as part of your own project sources (vendoring) or you can add the sml.pkg file to your project sources and make the smlpkg sync command part of your build process.

Authors

Copyright (c) 2019-2021 Martin Elsman, University of Copenhagen.

License

See LICENSE (MIT License).