CONFIGURATION.md

Configuration Format

The floskell configuration file is a JSON file. The basic structure is as follows:

{
  "language": "Haskell2010",
  "extensions": [],
  "style": "base",
  "formatting": {
    "penalty": {...},
    "layout": {...},
    "indent": {...},
    "align": {...},
    "group": {...},
    "op": {...},
    "options": {...}
    }
  }
}

Parser Settings

• language (Haskell2010): The Haskell language standard for parsing source files. Either Haskell98 or Haskell2010.

  {
    "language": "Haskell2010"
  }

• extensions ([]): A list of extensions to be enabled or disabled. Check the output of floskell --help for the full list of extensions. To disable an extension, prefix the extension with No.

  {
    "extensions": ["RecordWildCards", "NoTypeFamilies"]
  }

• fixities ([]): A list of additional infix declarations to use while parsing. Check the output of floskell --help for a list of built-in declarations.

  {
    "fixities": ["infixr 9 ."]
  }

Style Definition

• style (base): The formatting style to use. The style can be fine-tuned using the formatting configuration element. Check the output of floskell --help for the full list of styles.

• formatting ({}): Formatting settings, applied on top of the selected style.

Line Penalty

• penalty: Defines the parameters for the penalty function used to judge the overall layout.

  • indent (1): Penalty for each indentation character.
  • linebreak (10): Penalty for each line.
  • max-line-length (80): Character limit for each line.
  • overfull (10): Penalty for each character over the line limit.
  • overfull-once (200): Penalty for each overfull line.

Layout Rules

• layout: Defines the accepted layout choices for all configurable language constructs.

  Allowed values are flex, vertical, or try-oneline.

  • app (flex): Function application
  • con-decls (flex): Data constructor declarations
  • declaration (flex): Declarations
  • export-spec-list (flex): Module export list
  • if (flex): If-then-else
  • import-spec-list (flex): Module import lists
  • infix-app (flex): Infix operator application
  • let (flex): Let-in
  • list-comp (flex): List comprehensions
  • record (flex): Record declaration, construction, and update
  • type (flex): Types in signatures

Indentation Rules

• indent: Defines the indentation choices for all configurable language constructs.

  Allowed values (except for onside, deriving, where) are align, indent-by n, and align-or-indent-by n.

  Allowed values for onside are all integers greater than zero.

  Allowed values for deriving and where are all integers greater than or equal to zero.

  • onside (4): Onside indentation
  • deriving (4): Indentation for deriving lists
  • where (2): Indentation for where keyword after functions
  • case (indent-by 4): Case analysis
  • class (indent-by 4): Class and instance declarations
  • do (indent-by 4): Do and recursive do blocks
  • export-spec-list (indent-by 4): Module export list
  • if (indent-by 4): If-then-else
  • import-spec-list (indent-by 4): Module import lists
  • let (indent-by 4): Let bindings
  • let-binds (indent-by 4): Let bindings
  • let-in (indent-by 4): Expression in let
  • multi-if (indent-by 4): Guards and multi-way if
  • typesig (indent-by 4): Type signatures
  • where-binds (indent-by 2): Bindings in where block after functions

Tabstop Alignment

• align: Defines the enabled tabstop alignments and their limitations.

  Allowed values, except for limits, are true and false.

  The item limits must be a list with two integers, the first integer is a number of character (absolute limit), the second a percentage (relative limit). Alignment will be disabled if the length of any inserted padding is larger than absolute limit and is larger than relative limit of the maximum field length (tabstop column minus indentation).

  • limits ([10, 25]): Alignment limits
  • case (false): Case patterns
  • class (false): Declarations inside class and instance declarations
  • import-module (false): Names of imported modules
  • import-spec (false): Module import lists
  • let-binds (false): Let bindings
  • matches (false): Function match clauses
  • record-fields (false): Record field assignments and type signatures
  • where (false): Declarations in where bindings for functions

Whitespace Rules

• group: Defines whitespace rules for parentheses, brackets, braces, and other enclosing punctuation characters.

  The group item is a map from enclosing punctuation (identified by the opening characters) and optional context to a whitespace configuration. The key can be either

  • default: Defines the fallback whitespace configuration,

  • * in <context>: Defines the default whitespace configuration within the given context,

  • <punct> in *: Defines the default whitespace configuration for the given punctuation, or

  • <punct> in <context>: Defines the whitespace configuration for the given punctuation within the given context,

  where context is one of declaration, type, pattern, expression, or other.

  The value is an object with the following fields:

  • spaces: Where to insert spaces.
  • linebreaks: Where to insert linebreaks.
  • force-linebreak: Whether to enforce vertical layout.

  An example:

  {
    "group": {
      "default": {
        "spaces": "none",
        "linebreaks": "after",
        "force-linebreak": false
      },
      "(": {
        "spaces": "both",
        "linebreaks": "after",
        "force-linebreak": false
      },
      "( in pattern": {
        "spaces": "none",
        "linebreaks": "none",
        "force-linebreak": false
      }
    }
  }

• op: Defines whitespacce rules for infix operators.

  See group above.

Other Style Options

• options: Defines additional formatting rules for module heads.

  • align-sum-type-decl (false): Whether to align = with | in the declaration of sum types.
  • preserve-vertical-space (false): Whether to preserve additional vertical space between declarations, statements, and a few other places.
  • decl-no-blank-lines ([]): Where to (not) insert blank lines between declarations (module, class, instance, where).
  • sort-import-lists (false): Whether to sort import statements by the name of the imported module.
  • sort-imports (false): How to sort import lists (see below).
  • sort-pragmas (false): Whether to sort module pragmas (LANGUAGE, OPTION, and ANN).
  • flexible-oneline (false): Allow do, mdo, case ... of, \case, and \... -> in try-oneline layout.
  • split-language-pragmas (false): Whether to split LANGUAGE pragmas.
  • align-let-binds-and-in-expr (false): Whether to align let bindings and the in expression, in a let expression.

Sorting Imports

There are three import sorting modes:

• No sorting (sort-imports: false). This mode will retain the order of imports and any blank lines between imports.

• Sort imports and group by the first component of the module path (sort-imports: true): Data.Maybe goes with Data.Either, Control.Monad goes with Control.Applicative.

  This mode is equivalent to:

  "sort-imports": [
    {
      "prefixes": [""],
      "order": "grouped"
    }
  ]

• Configurable grouping and sorting (sort-imports: [...]). sort-imports is a list of group declarations, where each group defines a set of module prefixes and an order.

  Each import is assigned to a group based on the longest matching prefix. Imports without a match are assigned to an implicit final group with order keep. You can manually collect all left-over imports by specifying a group with an empty prefix.

  The order can be one of keep, sorted, or grouped. keep retains the manual order of imports of the input file, sorted will sort imports within the group, and grouped will sort and then group imports within the group based on the first component after the common prefix of the group's prefixes.

  For example:

  "sort-imports": [
    {
      "prefixes": [ "" ],
      "order": "grouped"
    },
    {
      "prefixes": [ "Floskell" ],
      "order": "sorted"
    },
    {
      "prefixes": [ "Test" ],
      "order": "grouped"
    },
    {
      "prefixes": [ "Prelude" ],
      "order": "sorted"
    }
  ]

  This configuration will first place all 'generic' imports, sorted and grouped on the top-level module name component. E.g. all of "Control", then "Data", etc.

  After that, there is a sorted section of 'local' imports (everything within "Floskell"), without any subdivision.

  Following are all imports from "Test", again sorted and grouped based on the first component after "Test".

  Lastly, any imports of "Prelude".