Language.Haskell.HLint3

WARNING: This module represents the evolving second version of the HLint API. It will be renamed to drop the "3" 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]

Documentation

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

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 a your server with untrusted input.

applyHints :: [Classify] -> Hint -> [(Module_, [Comment])] -> [Idea]

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 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

An idea suggest by a Hint.

Constructors

Idea

Fields

• ideaModule :: String

  The module the idea applies to, may be "" if the module cannot be determined or is a result of cross-module hints.

• ideaDecl :: String

  The declaration the idea applies to, typically the function name, but may be a type name.

• ideaSeverity :: Severity

  The severity of the idea, e.g. Warning.

• ideaHint :: String

  The name of the hint that generated the idea, e.g. "Use reverse".

• ideaSpan :: SrcSpan

  The source code the idea relates to.

• ideaFrom :: String

  The contents of the source code the idea relates to.

• ideaTo :: Maybe String

  The suggested replacement, or Nothing for no replacement (e.g. on parse errors).

• ideaNote :: [Note]

  Notes about the effect of applying the replacement.

• ideaRefactoring :: [Refactoring SrcSpan]

  How to perform this idea

Instances

Eq Idea

Methods

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

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

Ord Idea

Methods

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

Methods

showsPrec :: Int -> Idea -> ShowS

show :: Idea -> String

showList :: [Idea] -> ShowS

data Severity

How severe an issue is.

Constructors

Ignore

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

Suggestion

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

Warning

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

Error

Available as a setting for the user.

Instances

Bounded Severity

Methods

minBound :: Severity

maxBound :: Severity

Enum Severity

Methods

succ :: Severity -> Severity

pred :: Severity -> Severity

toEnum :: Int -> Severity

fromEnum :: Severity -> Int

enumFrom :: Severity -> [Severity]

enumFromThen :: Severity -> Severity -> [Severity]

enumFromTo :: Severity -> Severity -> [Severity]

enumFromThenTo :: Severity -> Severity -> Severity -> [Severity]

Eq Severity

Methods

(==) :: Severity -> Severity -> Bool

(/=) :: Severity -> Severity -> Bool

Ord Severity

Methods

compare :: Severity -> Severity -> Ordering

(<) :: Severity -> Severity -> Bool

(<=) :: Severity -> Severity -> Bool

(>) :: Severity -> Severity -> Bool

(>=) :: Severity -> Severity -> Bool

max :: Severity -> Severity -> Severity

min :: Severity -> Severity -> Severity

Read Severity

Methods

readsPrec :: Int -> ReadS Severity

readList :: ReadS [Severity]

readPrec :: ReadPrec Severity

readListPrec :: ReadPrec [Severity]

Show Severity

Methods

showsPrec :: Int -> Severity -> ShowS

show :: Severity -> String

showList :: [Severity] -> ShowS

data Note

A note describing the impact of the replacement.

Constructors

IncreasesLaziness

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

DecreasesLaziness

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.

Note String

An arbitrary note.

Instances

Eq Note

Methods

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

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

Ord Note

Methods

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

Methods

showsPrec :: Int -> Note -> ShowS

show :: Note -> String

showList :: [Note] -> ShowS

Settings

data Classify

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

Constructors

Classify

Fields

• classifySeverity :: Severity

  Severity to set the Idea to.

• classifyHint :: String

  Match on Idea field ideaHint.

• classifyModule :: String

  Match on Idea field ideaModule.

• classifyDecl :: String

  Match on Idea field ideaDecl.

Instances

Show Classify

Methods

showsPrec :: Int -> Classify -> ShowS

show :: Classify -> String

showList :: [Classify] -> ShowS

getHLintDataDir :: IO FilePath

Get the Cabal configured data directory of HLint.

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

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)

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], [Either HintBuiltin HintRule])

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

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

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.

Hints

data HintBuiltin

A list of the builtin hints wired into HLint. This list is likely to grow over time.

Constructors

HintList

HintListRec

HintMonad

HintLambda

HintBracket

HintNaming

HintPattern

HintImport

HintExport

HintPragma

HintExtensions

HintUnsafe

HintDuplicate

HintRestrict

HintComment

HintNewType

Instances

Bounded HintBuiltin

Methods

minBound :: HintBuiltin

maxBound :: HintBuiltin

Enum HintBuiltin

Methods

succ :: HintBuiltin -> HintBuiltin

pred :: HintBuiltin -> HintBuiltin

toEnum :: Int -> HintBuiltin

fromEnum :: HintBuiltin -> Int

enumFrom :: HintBuiltin -> [HintBuiltin]

enumFromThen :: HintBuiltin -> HintBuiltin -> [HintBuiltin]

enumFromTo :: HintBuiltin -> HintBuiltin -> [HintBuiltin]

enumFromThenTo :: HintBuiltin -> HintBuiltin -> HintBuiltin -> [HintBuiltin]

Eq HintBuiltin

Methods

(==) :: HintBuiltin -> HintBuiltin -> Bool

(/=) :: HintBuiltin -> HintBuiltin -> Bool

Ord HintBuiltin

Methods

compare :: HintBuiltin -> HintBuiltin -> Ordering

(<) :: HintBuiltin -> HintBuiltin -> Bool

(<=) :: HintBuiltin -> HintBuiltin -> Bool

(>) :: HintBuiltin -> HintBuiltin -> Bool

(>=) :: HintBuiltin -> HintBuiltin -> Bool

max :: HintBuiltin -> HintBuiltin -> HintBuiltin

min :: HintBuiltin -> HintBuiltin -> HintBuiltin

Show HintBuiltin

Methods

showsPrec :: Int -> HintBuiltin -> ShowS

show :: HintBuiltin -> String

showList :: [HintBuiltin] -> ShowS

data HintRule

A LHS ==> RHS style hint rule.

Constructors

HintRule

Fields

• hintRuleSeverity :: Severity

  Default severity for the hint.

• hintRuleName :: String

  Name for the hint.

• hintRuleScope :: Scope

  Module scope in which the hint operates.

• hintRuleLHS :: Exp_

  LHS

• hintRuleRHS :: Exp_

  RHS

• hintRuleSide :: Maybe Exp_

  Side condition, typically specified with where _ = ....

• hintRuleNotes :: [Note]

  Notes about application of the hint.

Instances

Show HintRule

Methods

showsPrec :: Int -> HintRule -> ShowS

show :: HintRule -> String

showList :: [HintRule] -> ShowS

data Hint

Functions to generate hints, combined using the Monoid instance.

Constructors

Hint

Fields

• hintModules :: [Setting] -> [(Scope, Module_)] -> [Idea]

  Given a list of modules (and their scope information) generate some Ideas.

• hintModule :: [Setting] -> Scope -> Module_ -> [Idea]

  Given a single module and its scope information generate some Ideas.

• hintDecl :: [Setting] -> Scope -> Module_ -> Decl_ -> [Idea]

  Given a declaration (with a module and scope) generate some Ideas. This function will be partially applied with one module/scope, then used on multiple Decl values.

• hintComment :: [Setting] -> Comment -> [Idea]

  Given a comment generate some Ideas.

Instances

Monoid Hint

Methods

mempty :: Hint

mappend :: Hint -> Hint -> Hint

mconcat :: [Hint] -> Hint

resolveHints :: [Either HintBuiltin HintRule] -> Hint

Transform a list of HintBuiltin or HintRule into a Hint.

Scopes

data Scope

Data type representing the modules in scope within a module. Created with scopeCreate and queried with scopeMatch and scopeMove. Note that the mempty Scope is not equivalent to scopeCreate on an empty module, due to the implicit import of Prelude.

Instances

Show Scope

Methods

showsPrec :: Int -> Scope -> ShowS

show :: Scope -> String

showList :: [Scope] -> ShowS

Monoid Scope

Methods

mempty :: Scope

mappend :: Scope -> Scope -> Scope

mconcat :: [Scope] -> Scope

scopeCreate :: Module_ -> Scope

Create a Scope value from a module, based on the modules imports.

scopeMatch :: (Scope, QName S) -> (Scope, QName S) -> Bool

Given a two names in scopes, could they possibly refer to the same thing. This property is reflexive.

scopeMove :: (Scope, QName S) -> Scope -> QName S

Given a name in a scope, and a new scope, create a name for the new scope that will refer to the same thing. If the resulting name is ambiguous, it picks a plausible candidate.

Haskell-src-exts

parseModuleEx :: ParseFlags -> FilePath -> Maybe String -> IO (Either ParseError (Module_, [Comment]))

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.

defaultParseFlags :: ParseFlags

Default value for ParseFlags.

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

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

data ParseError

A parse error from parseModuleEx.

Constructors

ParseError

Fields

• parseErrorLocation :: SrcLoc

  Location of the error.

• parseErrorMessage :: String

  Message about the cause of the error.

• parseErrorContents :: String

  Snippet of several lines (typically 5) including a > character pointing at the faulty line.

data ParseFlags

Created with defaultParseFlags, used by parseModuleEx.

Constructors

ParseFlags

Fields

• 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

What C pre processor should be used.

Constructors

NoCpp

No pre processing is done.

CppSimple

Lines prefixed with # are stripped.

Cpphs CpphsOptions

The cpphs library is used.