# Visual Haskell User's Guide

Simon
Marlow
simonmar@microsoft.com
Krasimir
Angelov
kr.angelov@gmail.com

## Introduction

Visual Haskell is a plugin for Microsoft's Visual Studio development environment to support development of Haskell software. Like the other Visual languages, Visual Haskell integrates with the Visual Studio editor to provide interactive features to aid Haskell development, and it enables the construction of projects consisting of multiple Haskell modules.

### Installing Visual Haskell

In order to use Visual Haskell, you need Visual Studio .NET 2003. Right now, this is the only supported version of Visual Studio - unfortunately we haven't yet added support for the 2005 Beta. The Express languages (Visual C++ Express etc.) also will not work, because they don't have support for plugins.

You don't need to install GHC separately: Visual Haskell is bundled with a complete GHC distribution, and various other tools (Happy, Alex, Haddock).

The latest Visual Haskell installer can be obtained from here:

`http://www.haskell.org/visualhaskell/`

### Release Notes

#### Version 0.0, first release

This release is a technology preview, and should be considered alpha quality. It works for us, but you are fairly likely to encounter problems. If you're willing to try it out and report bugs, we'd be grateful for the feedback.

- This release of Visual Haskell is bundled with a development snapshot of GHC, version 6.5 from around 14 September 2005. This version of GHC is used to provide the interactive editing features, and will be used to compile all code inside Visual Haskell. It is possible that in future releases we may be able to relax this tight coupling between Visual Haskell and the bundled GHC.

  Please note that future releases of Visual Haskell will update the compiler, and hence the packages, and so may break your code. Also note that because the bundled GHC is not a released version, it may have bugs and quirks itself: please report them as usual to glasgow-haskell-bugs@haskell.org.

- We're not making source code for the plugin generally available at this time, due to licensing restrictions on the Visual Studio APIs that the plugin uses (for more information see Visual Studio Extensibility Center). If you're interested in contributing to Visual Haskell, please get in touch with the authors.

### Getting support, reporting bugs

Please report bugs to glasgow-haskell-bugs@haskell.org (subscribe here), clearly indicating that your bug report relates to Visual Haskell, and giving as much information as possible so that we can reproduce the bug. Even if you can't reproduce the bug reliably, it is still useful to report what you've seen.

For help and support, use the glasgow-haskell-users@haskell.org (subscribe here) mailing list.

### License

> Copyright © Microsoft Corporation. All rights reserved.

> Copyright © The University of Glasgow. All rights reserved.

> Copyright © Krasimir Angelov. All rights reserved.

> Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

> - Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

> - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

> - The names of the copyright holders may not be used to endorse or promote products derived from this software without specific prior written permission.

> THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

## Using Visual Haskell

### Overview of features

The following features are provided in the Visual Studio editor when editing Haskell code:

- Automatic checking of code as you type, and visual indication of parse errors, scoping errors and type errors.

- Quick info: hovering the mouse over an identifier pops up an information box, including the type of the identifier.

- A drop-down bar at the top of the editing window lists the top-level declarations in the module, and allows quick navigation to a declaration.

- Name completion for identifiers in scope: press Ctrl+Space after a partial identifier to see the completions.

- Go to declaration: right clicking on an identifier and selecting "Go to declaration" will jump the cursor to the declaration of the identifier. This works for locally-defined identifiers and those defined in another module of the project; it does not work for library functions currently.

The following features are provided by the project system for constructing Haskell projects:

- Multi-module Haskell projects are fully supported, based on the Cabal infrastructure. A project in Visual Haskell is a Cabal package, and vice-versa. A Visual Studio project can be taken to a machine without Visual Haskell and built/installed as a normal Cabal package, and an existing Cabal package can be edited directly in Visual Haskell This works as long as the Cabal package is using Cabal's simple build system; Cabal packages using their own build systems cannot be edited in Visual Haskell. .

- Editing of most of the package meta-data is supported through the project property pages.

- The interactive editing features work across multiple modules in a project. When one module is edited, changes are automatically propagated to dependent modules, even if the edited module has not yet been saved.

- Building is supported through the Cabal build system, and build errors are communicated back to the editor and placed in the task list. Use any of the Visual Studio build commands (e.g. Build Project from the context menu on the project, or Ctrl-Shift-B to build the whole solution).

Additionally, Visual Haskell is bundled with a large collection of documentation: the GHC manual, the hierarchical libraries reference, and other material all of which can be browsed within Visual Studio itself.

### Getting Started

After installing Visual Haskell, start up Visual Studio as you would normally, and observe that on the splash screen where it lists the supported languages you should now see an icon for Visual Haskell (if you don't see this, something has gone wrong... please let us know).

Firstly, take a look at the bundled documentation. Go to Help->Contents, and you should see the “Visual Haskell Help Collection”, which contains a large collection of GHC and Haskell-related documentaiton, including this document.

To start using Visual Haskell right away, create a new project (File->New->Project...). Select one of the Haskell project types (Console Application or Library Package), and hit Ok. The project will be created for you, and an example module added: `Main.hs` for an application, or `Module1.hs` for a library.

You can now start adding code to `Main.hs`, or adding new modules. To add a new module, right-click on the `src` directory, and select Add->New Item. Visual Haskell supports hierarchical modules too: you can add new folders using the same Add menu to create new nodes in the hierarchy.

If you have any errors in your code, they will be underlined with a red squiggly line. Select the Tasks window (usually a tab near the bottom of the Visual Studio window) to see the error messages, and click on an error message to jump to it in the editor.

To build the program, hit Ctrl-Shift-B, or select one of the options from the Build menu.

### Editing Haskell code

(ToDo: more detail here)

Your module must be plain Haskell (`.hs`) for the interactive features to fully work. If your module is pre-processed with CPP or Literate Haskell, then Visual Haskell will only check the module when it is saved; between saves the source will not be checked for errors and the type information will not be updated. If the source file is pre-processed with Happy or another pre-processor, then you may have to build the project before the type information will be updated (because the pre-processor is only run as part of the build process). Pre-processed source files work fine in a multi-module setting; you can have modules which depend on a pre-processed module and full interactive checking will still be available in those modules.

Because Visual Haskell is using GHC as a backend for its interactive editing features, it supports the full GHC language, including all extensions.

### Using Projects

(ToDo: more detail here)