haskell-formatter alternatives and similar packages
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README
Haskell Formatter
The Haskell Formatter formats Haskell source code. It is strict in that it fundamentally rearranges code.
Installation
Install it by running
stack install haskell-formatter
or
cabal new-install haskell-formatter
You are ready when
haskell-formatter --help
works.
Usage
Basics
Read source code from Input.hs
, format it, and write it to Output.hs
by
haskell-formatter --input Input.hs --output Output.hs
If the input or output file is not given, it defaults to the corresponding standard stream. This allows commands like
haskell-formatter < Input.hs
To format a file in-place, use the --force
option as in
# Warning: this overwrites the file `Code.hs`.
haskell-formatter --force --input Code.hs --output Code.hs
For more help about the usage, call
haskell-formatter --help
Formatting Many Files
For a diff of how code in the current folder would be formatted, without actually changing anything, run
find . -name '*.hs' -type f -print0 \
| xargs -0 -n 1 bash -c 'haskell-formatter < "$@" | diff -u "$@" -' --
The returned exit status is nonzero if there are unformatted files. This may be useful for continuous integration.
To format any *.hs
files in a folder code/
or (recursively) in its subfolders, run
# Warning: this overwrites files, so better back them up first.
find code/ -name '*.hs' -type f -print0 \
| xargs -0 -I {} -n 1 haskell-formatter --force --input {} --output {}
Style Configuration
The formatting style can be configured with a file referred by the --style
option. For instance, the call
haskell-formatter --style my_style.yaml --input Input.hs --output Output.hs
uses my_style.yaml
as a style file. Such files are in the YAML format. The following is an [example style file](testsuite/resources/examples/default_style.yaml), which at the same time shows the available keys with their default values.
<!--- GitHub does currently not allow to include files (https://github.com/github/markup/issues/346).
Thus, the file content is replicated here. There is a test which checks that the strings of both sources are equal. --->
# Lines should be no longer than this length in characters.
line_length_limit: 80
# How much to spread code over multiple lines instead of trying to fill a single
# line. More precisely, this guides the ratio of "line_length_limit" to the
# ribbon length (the number of characters on a line without leading and trailing
# whitespace). Only the lowest value of 1 forces "line_length_limit" to be
# applied strictly.
# Reference: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.38.8777
ribbons_per_line: 1
# More than this number of empty lines in succession are merged.
successive_empty_lines_limit: 1
# Indentation lengths in characters.
indentations:
class: 8 # "class" and "instance" declarations.
do: 3 # "do" notation.
case: 4 # Body of "case" expressions.
let: 4 # Declarations in "let" expressions.
where: 6 # Declarations in "where" clauses.
onside: 2 # Continuation lines which would otherwise be offside.
# Decides which parts of the code to sort.
order:
# Sequence of import declarations.
import_declarations: true
# Entities of import lists.
import_entities: true
Related Projects
You may like to have a look at the following projects, which aim at formatting Haskell code, too.
*Note that all licence references and agreements mentioned in the haskell-formatter README section above
are relevant to that project's source code only.