Tags

Introduction

"Tags" are a listing of source code definitions in a group of files, together with their precise location, often used by text editors to quickly jump around in a program. For example, they allow you in a editor that supports tags to jump to the definition of a function when you come across a use of that function. ctags (for C) was the first tag-generation program. See the wikipedia article for more information.

There are currently a number of different ways to generate tags with Haskell.

Tags Formats

Tag files can be produced in a number of different formats supported by different editors. The two most common formats are 'ctags', which is supported by Vim and others, and 'etags', which is supported by Emacs. Note that the default names for the file in ctags format and the file in etags format are 'tags' and 'TAGS' respectively

Haskell tag generators

GHC

• GHC can generate tag files from GHCi. Use either the ':ctags' or ':etags' commands to produce a tags file for the currently loaded modules.

For example:

echo ":ctags" | ghci -v0 Main.hs

echo ":etags" | ghci -v0 Main.hs

Actively developed

• Hasktags: Can produce either a ctags or etags compatible tag file. Uses its own parser.
• hothasktags: Knows about import lists and qualified imports. Vim tags only. Uses haskell-src-exts for parsing.
• lushtags: Designed to have smooth integration with the Vim Tagbar plugin.

Other

• haskdogs: Wrapper script for hasktags. (last update 2013)
• fast-tags: Incremental Vim tag generation. Designed to be fast. Uses its own parser. (last update 2012)
• gasbag: Attempts to choose the best available definition for a given tag. Will notice bindings that don't have an accompanying type signature. (last update 2011)
• htags: Haskell 98 only. Uses haskell-src for parsing. (last update 2008)

GHC development

• Use `make tags` in the root of the ghc source tree when hacking on GHC itself.

• Use `make TAGS` to generate Emacs tags.

You can also find the source code for a tag generator in Chris Ryder and Simon Thompson paper on porting the Haskell Refactoring tool, HaRe, to the GHC API.

More Information

Vim

• Using tags in Vim
• :help tags
• insert-mode tag completion (ctrl-x ctrl-])
• :help cursorhold-example
• Vim plugin to view all tags in a window
• Another plugin; newer's not always better, but this is still actively maintained as of 2012

Others

• NEdit documentation for using tags
• Chapter 14 of the BBEdit manual covers using tags