Safe Haskell | None |
---|---|
Language | Haskell2010 |
Dig metadata out of the description of your project.
This uses the evil Template Haskell to run code at compile time that parses the .cabal file for your Haskell project and extracts various meaningful fields.
Synopsis
- data Version
- fromPackage :: Q Exp
- versionNumberFrom :: Version -> String
- projectNameFrom :: Version -> String
- projectSynopsisFrom :: Version -> String
Documentation
Information about the version number of this piece of software and other
related metadata related to the project it was built from. This is supplied
to your program when you call configure
. This value
is used if the user requests it by specifying the --version
option on the
command-line.
Simply providing an overloaded string literal such as version "1.0"
will give you a Version
with that value:
{-# LANGUAGE OverloadedStrings #-} main ::IO
() main = do context <-configure
"1.0"None
(simple
...
For more complex usage you can populate a Version
object using the
fromPackage
splice below. You can then call various accessors like
versionNumberFrom
to access individual fields.
Splice
fromPackage :: Q Exp Source #
This is a splice which includes key built-time metadata, including the number from the version field from your project's .cabal file (as written by hand or generated from package.yaml).
While we generally discourage the use of Template Haskell by beginners (there are more important things to learn first) it is a way to execute code at compile time and that is what what we need in order to have the version number extracted from the .cabal file rather than requiring the user to specify (and synchronize) it in multiple places.
To use this, enable the Template Haskell language extension in your
Main.hs file. Then use the special $( ... )
"insert splice here"
syntax that extension provides to get a Version
object with the desired
metadata about your project:
{-# LANGUAGE TemplateHaskell #-} version ::Version
version = $(fromPackage
) main ::IO
() main = do context <-configure
versionNone
(simple
...
(Using Template Haskell slows down compilation of this file, but the upside of this technique is that it avoids linking the Haskell build machinery into your executable, saving you about 10 MB in the size of the resultant binary)
Internals
versionNumberFrom :: Version -> String Source #
projectNameFrom :: Version -> String Source #
projectSynopsisFrom :: Version -> String Source #