hlint-2.1.24: Source code suggestions

Safe HaskellNone




WARNING: This module represents the evolving version of the HLint API. It will be renamed to drop the "4" in the next major version.

This module provides a way to apply HLint hints. If you want to just run hlint in-process and collect the results see hlint. If you want to approximate the hlint experience with a more structured API try:

(flags, classify, hint) <- autoSettings
Right m <- parseModuleEx flags "MyFile.hs" Nothing
print $ applyHints classify hint [m]


hlint :: [String] -> IO [Idea] Source #

This function takes a list of command line arguments, and returns the given hints. To see a list of arguments type hlint --help at the console. This function writes to the stdout/stderr streams, unless --quiet is specified.

As an example:

do hints <- hlint ["src", "--ignore=Use map","--quiet"]
   when (length hints > 3) $ error "Too many hints!"

Warning: The flags provided by HLint are relatively stable, but do not have the same API stability guarantees as the rest of the strongly-typed API. Do not run this function on your server with untrusted input.

applyHints :: [Classify] -> Hint -> [ModuleEx] -> [Idea] Source #

Given a way of classifying results, and a Hint, apply to a set of modules generating a list of Ideas. The Idea values will be ordered within a file.

Given a set of modules, it may be faster to pass each to applyHints in a singleton list. When given multiple modules at once this function attempts to find hints between modules, which is slower and often pointless (by default HLint passes modules singularly, using --cross to pass all modules together).

Idea data type

data Idea Source #

An idea suggest by a Hint.




Eq Idea Source # 
Instance details

Defined in Idea


(==) :: Idea -> Idea -> Bool #

(/=) :: Idea -> Idea -> Bool #

Ord Idea Source # 
Instance details

Defined in Idea


compare :: Idea -> Idea -> Ordering #

(<) :: Idea -> Idea -> Bool #

(<=) :: Idea -> Idea -> Bool #

(>) :: Idea -> Idea -> Bool #

(>=) :: Idea -> Idea -> Bool #

max :: Idea -> Idea -> Idea #

min :: Idea -> Idea -> Idea #

Show Idea Source # 
Instance details

Defined in Idea


showsPrec :: Int -> Idea -> ShowS #

show :: Idea -> String #

showList :: [Idea] -> ShowS #

data Severity Source #

How severe an issue is.



The issue has been explicitly ignored and will usually be hidden (pass --show on the command line to see ignored ideas).


Suggestions are things that some people may consider improvements, but some may not.


Warnings are suggestions that are nearly always a good idea to apply.


Available as a setting for the user.

data Note Source #

A note describing the impact of the replacement.



The replacement is increases laziness, for example replacing reverse (reverse x) with x makes the code lazier.


The replacement is decreases laziness, for example replacing (fst x, snd x) with x makes the code stricter.

RemovesError String

The replacement removes errors, for example replacing foldr1 (+) with sum removes an error on [], and might contain the text "on []".

ValidInstance String String

The replacement assumes standard type class lemmas, a hint with the note ValidInstance "Eq" "x" might only be valid if the x variable has a reflexive Eq instance.

RequiresExtension String

The replacement requires this extension to be available.

Note String

An arbitrary note.

Eq Note Source # 
Instance details

Defined in Config.Type


(==) :: Note -> Note -> Bool #

(/=) :: Note -> Note -> Bool #

Ord Note Source # 
Instance details

Defined in Config.Type


compare :: Note -> Note -> Ordering #

(<) :: Note -> Note -> Bool #

(<=) :: Note -> Note -> Bool #

(>) :: Note -> Note -> Bool #

(>=) :: Note -> Note -> Bool #

max :: Note -> Note -> Note #

min :: Note -> Note -> Note #

Show Note Source # 
Instance details

Defined in Config.Type


showsPrec :: Int -> Note -> ShowS #

show :: Note -> String #

showList :: [Note] -> ShowS #


data Classify Source #

How to classify an Idea. If any matching field is "" then it matches everything.




Show Classify Source # 
Instance details

Defined in Config.Type

getHLintDataDir :: IO FilePath Source #

Get the Cabal configured data directory of HLint.

autoSettings :: IO (ParseFlags, [Classify], Hint) Source #

The function produces a tuple containg ParseFlags (for parseModuleEx), and Classify and Hint for applyHints. It approximates the normal HLint configuration steps, roughly:

  1. Use findSettings with readSettingsFile to find and load the HLint settings files.
  2. Use parseFlagsAddFixities and resolveHints to transform the outputs of findSettings.

If you want to do anything custom (e.g. using a different data directory, storing intermediate outputs, loading hints from a database) you are expected to copy and paste this function, then change it to your needs.

argsSettings :: [String] -> IO (ParseFlags, [Classify], Hint) Source #

A version of autoSettings which respects some of the arguments supported by HLint. If arguments unrecognised by HLint are used it will result in an error. Arguments which have no representation in the return type are silently ignored.

findSettings :: (String -> IO (FilePath, Maybe String)) -> Maybe String -> IO ([Fixity], [Classify], Hint) Source #

Given a function to load a module (typically readSettingsFile), and a module to start from (defaults to hlint.yaml) find the information from all settings files.

readSettingsFile :: Maybe FilePath -> String -> IO (FilePath, Maybe String) Source #

Given a directory (or Nothing to imply getHLintDataDir), and a module name (e.g. HLint.Default), find the settings file associated with it, returning the name of the file, and (optionally) the contents.

This function looks for all settings files starting with HLint. in the directory argument, and all other files relative to the current directory.


data Hint Source #

Functions to generate hints, combined using the Monoid instance.

Semigroup Hint Source # 
Instance details

Defined in Hint.Type


(<>) :: Hint -> Hint -> Hint #

sconcat :: NonEmpty Hint -> Hint #

stimes :: Integral b => b -> Hint -> Hint #

Monoid Hint Source # 
Instance details

Defined in Hint.Type


mempty :: Hint #

mappend :: Hint -> Hint -> Hint #

mconcat :: [Hint] -> Hint #

resolveHints :: Hint -> Hint Source #

The identity function. In previous versions of HLint this function was useful. Now, it isn't.

Parse files

data ModuleEx Source #

Result of parseModuleEx, representing a parsed module.

parseModuleEx :: ParseFlags -> FilePath -> Maybe String -> IO (Either ParseError ModuleEx) Source #

Parse a Haskell module. Applies the C pre processor, and uses best-guess fixity resolution if there are ambiguities. The filename - is treated as stdin. Requires some flags (often defaultParseFlags), the filename, and optionally the contents of that file. This version uses both hs-src-exts AND ghc-lib.

parseFlagsAddFixities :: [Fixity] -> ParseFlags -> ParseFlags Source #

Given some fixities, add them to the existing fixities in ParseFlags.

data ParseError Source #

A parse error.




data ParseFlags Source #

Created with defaultParseFlags, used by parseModuleEx.




  • cppFlags :: CppFlags

    How the file is preprocessed (defaults to NoCpp).

  • hseFlags :: ParseMode

    How the file is parsed (defaults to all fixities in the base package and most non-conflicting extensions).

data CppFlags Source #

What C pre processor should be used.



No pre processing is done.


Lines prefixed with # are stripped.

Cpphs CpphsOptions

The cpphs library is used.