ListLike-3.1.7.1: Generic support for list-like structures

Portabilityportable
Stabilityprovisional
MaintainerJohn Goerzen <jgoerzen@complete.org>
Safe HaskellSafe-Inferred

Data.ListLike

Contents

Description

Generic operations over list-like structures

Written by John Goerzen, jgoerzen@complete.org

Please start with the introduction at Data.ListLike.

Synopsis

Introduction

Welcome to ListLike.

This module provides abstractions over typical list operations. It is designed to let you freely interchange different ways to represent sequences of data. It works with lists, various types of ByteStrings, and much more.

In this module, you'll find generic versions of most of the functions you're used to using in the Prelude, Data.List, and System.IO. They carry the same names, too. Therefore, you'll want to be careful how you import the module. I suggest using: 

import qualified Data.ListLike as LL

Then, you can use LL.fold, LL.map, etc. to get the generic version of the functions you want. Alternatively, you can hide the other versions from Prelude and import specific generic functions from here, such as: 

import Prelude hiding (map)
import Data.ListLike (map)

The module Data.ListLike actually simply re-exports the items found in a number of its sub-modules. If you want a smaller subset of Data.ListLike, look at the documentation for its sub-modules and import the relevant one.

In most cases, functions here can act as drop-in replacements for their list-specific counterparts. They will use the same underlying implementations for lists, so there should be no performance difference.

You can make your own types instances of ListLike as well. For more details, see the notes for the ListLike typeclass.

Creation & Basic Functions

List transformations

Conversions

Reducing lists (folds), from FoldableLL

Special folds

and :: ListLike full Bool => full -> BoolSource

Returns True if all elements are True

or :: ListLike full Bool => full -> BoolSource

Returns True if any element is True

sum :: (Num a, ListLike full a) => full -> aSource

The sum of the list

product :: (Num a, ListLike full a) => full -> aSource

The product of the list

fold :: (FoldableLL full item, Monoid item) => full -> itemSource

Combine the elements of a structure using a monoid. fold = foldMap id

foldMap :: (FoldableLL full item, Monoid m) => (item -> m) -> full -> mSource

Map each element to a monoid, then combine the results

Building lists

Scans

Accumulating maps

Infinite lists

Unfolding

Sublists

Extracting sublists

Predicates

Searching lists

Searching by equality

Searching with a predicate

Indexing lists

Zipping and unzipping lists

zip :: (ListLike full item, ListLike fullb itemb, ListLike result (item, itemb)) => full -> fullb -> resultSource

Takes two lists and returns a list of corresponding pairs.

zipWith :: (ListLike full item, ListLike fullb itemb, ListLike result resultitem) => (item -> itemb -> resultitem) -> full -> fullb -> resultSource

Takes two lists and combines them with a custom combining function

unzip :: (ListLike full (itema, itemb), ListLike ra itema, ListLike rb itemb) => full -> (ra, rb)Source

Converts a list of pairs into two separate lists of elements

Monadic Operations

sequence_ :: (Monad m, FoldableLL full (m item)) => full -> m ()Source

Evaluate each action, ignoring the results. Same as mapM_ id.

mapM_ :: (Monad m, FoldableLL full item) => (item -> m b) -> full -> m ()Source

A map in monad space, discarding results.

Input and Output

class ListLike full item => ListLikeIO full item | full -> item whereSource

An extension to ListLike for those data types that support I/O. These functions mirror those in System.IO for the most part. They also share the same names; see the comments in Data.ListLike for help importing them.

Note that some types may not be capable of lazy reading or writing. Therefore, the usual semantics of System.IO functions regarding laziness may or may not be available from a particular implementation.

Minimal complete definition:

  • hGetLine
  • hGetContents
  • hGet
  • hGetNonBlocking
  • hPutStr

Methods

hGetLine :: Handle -> IO fullSource

Reads a line from the specified handle

hGetContents :: Handle -> IO fullSource

Read entire handle contents. May be done lazily like hGetContents.

hGet :: Handle -> Int -> IO fullSource

Read specified number of bytes. See hGet for particular semantics.

hGetNonBlocking :: Handle -> Int -> IO fullSource

Non-blocking read. See hGetNonBlocking for more.

hPutStr :: Handle -> full -> IO ()Source

Writing entire data.

hPutStrLn :: Handle -> full -> IO ()Source

Write data plus newline character.

getLine :: IO fullSource

Read one line

getContents :: IO fullSource

Read entire content from stdin. See hGetContents.

putStr :: full -> IO ()Source

Write data to stdout.

putStrLn :: full -> IO ()Source

Write data plus newline character to stdout.

interact :: (full -> full) -> IO ()Source

Interact with stdin and stdout by using a function to transform input to output. May be lazy. See interact for more.

readFile :: FilePath -> IO fullSource

Read file. May be lazy.

writeFile :: FilePath -> full -> IO ()Source

Write data to file.

appendFile :: FilePath -> full -> IO ()Source

Append data to file.

Instances

Special lists

Strings

"Set" operations

Ordered lists

Generalized functions

The "By" operations

User-supplied equality (replacing an Eq context)

User-supplied comparison (replacing an Ord context)

The "generic" operations

Notes on specific instances

Lists

Functions for operating on regular lists almost all use the native implementations in Data.List, Prelude, or similar standard modules. The exceptions are:

Arrays

Array is an instance of ListLike. Here are some notes about it:

  • The index you use must be an integral
  • ListLike functions that take an index always take a 0-based index for compatibility with other ListLike instances. This is translated by the instance functions into the proper offset from the bounds in the Array.
  • ListLike functions preserve the original Array index numbers when possible. Functions such as cons will reduce the lower bound to do their job. snoc and append increase the upper bound. drop raises the lower bound and take lowers the upper bound.
  • Functions that change the length of the array by an amount not known in advance, such as filter, will generate a new array with the lower bound set to 0. Furthermore, these functions cannot operate on infinite lists because they must know their length in order to generate the array. hGetContents and its friends will therefore require the entire file to be read into memory before processing is possible.
  • empty, singleton, and fromList also generate an array with the lower bound set to 0.
  • Many of these functions will generate runtime exceptions if you have not assigned a value to every slot in the array.

ByteStrings

Both strict and lazy ByteStreams can be used with ListLike.

ByteString ListLike instances operate on Word8 elements. This is because both Data.ByteString.ByteString and Data.ByteString.Char8.ByteString have the same underlying type. If you wish to use the Char8 representation, the newtype wrappers CharString and CharStringLazy are available.

Most ListLike operations map directly to ByteStream options. Notable exceptions:

  • map uses the ListLike implementation. rigidMap is more efficient. The same goes for concatMap vs. rigidConcatMap.
  • isInfixOf, sequence, mapM and similar monad operations, insert, union, intersect, sortBy, and similar functions are not implemented in ByteStream and use a naive default implementation.
  • The lazy ByteStream module implements fewer funtions than the strict ByteStream module. In some cases, default implementations are used. In others, notably related to I/O, the lazy ByteStreams are converted back and forth to strict ones as appropriate.

newtype CharString Source

Newtype wrapper around Data.ByteString.Char8.ByteString, this allows for ListLike instances with Char elements.

Constructors

CS 

Fields

unCS :: ByteString
 

Instances

newtype CharStringLazy Source

Newtype wrapper around Data.ByteString.Lazy.Char8.ByteString, this allows for ListLike instances with Char elements.

Constructors

CSL 

Fields

unCSL :: ByteString
 

Instances

Base Typeclasses

The ListLike class

class (FoldableLL full item, Monoid full) => ListLike full item | full -> item whereSource

The class implementing list-like functions.

It is worth noting that types such as Map can be instances of ListLike. Due to their specific ways of operating, they may not behave in the expected way in some cases. For instance, cons may not increase the size of a map if the key you have given is already in the map; it will just replace the value already there.

Implementators must define at least:

  • singleton
  • head
  • tail
  • null or genericLength

Methods

empty :: fullSource

The empty list

singleton :: item -> fullSource

Creates a single-element list out of an element

cons :: item -> full -> fullSource

Like (:) for lists: adds an element to the beginning of a list

snoc :: full -> item -> fullSource

Adds an element to the *end* of a ListLike.

append :: full -> full -> fullSource

Combines two lists. Like (++).

head :: full -> itemSource

Extracts the first element of a ListLike.

last :: full -> itemSource

Extracts the last element of a ListLike.

tail :: full -> fullSource

Gives all elements after the head.

init :: full -> fullSource

All elements of the list except the last one. See also inits.

null :: full -> BoolSource

Tests whether the list is empty.

length :: full -> IntSource

Length of the list. See also genericLength.

map :: ListLike full' item' => (item -> item') -> full -> full'Source

Apply a function to each element, returning any other valid ListLike. rigidMap will always be at least as fast, if not faster, than this function and is recommended if it will work for your purposes. See also mapM.

rigidMap :: (item -> item) -> full -> fullSource

Like map, but without the possibility of changing the type of the item. This can have performance benefits for things such as ByteStrings, since it will let the ByteString use its native low-level map implementation.

reverse :: full -> fullSource

Reverse the elements in a list.

intersperse :: item -> full -> fullSource

Add an item between each element in the structure

concat :: (ListLike full' full, Monoid full) => full' -> fullSource

Flatten the structure.

concatMap :: ListLike full' item' => (item -> full') -> full -> full'Source

Map a function over the items and concatenate the results. See also rigidConcatMap.

rigidConcatMap :: (item -> full) -> full -> fullSource

Like concatMap, but without the possibility of changing the type of the item. This can have performance benefits for some things such as ByteString.

any :: (item -> Bool) -> full -> BoolSource

True if any items satisfy the function

all :: (item -> Bool) -> full -> BoolSource

True if all items satisfy the function

maximum :: Ord item => full -> itemSource

The maximum value of the list

minimum :: Ord item => full -> itemSource

The minimum value of the list

replicate :: Int -> item -> fullSource

Generate a structure with the specified length with every element set to the item passed in. See also genericReplicate

take :: Int -> full -> fullSource

Takes the first n elements of the list. See also genericTake.

drop :: Int -> full -> fullSource

Drops the first n elements of the list. See also genericDrop

splitAt :: Int -> full -> (full, full)Source

Equivalent to (take n xs, drop n xs). See also genericSplitAt.

takeWhile :: (item -> Bool) -> full -> fullSource

Returns all elements at start of list that satisfy the function.

dropWhile :: (item -> Bool) -> full -> fullSource

Drops all elements form the start of the list that satisfy the function.

span :: (item -> Bool) -> full -> (full, full)Source

The equivalent of (takeWhile f xs, dropWhile f xs)

break :: (item -> Bool) -> full -> (full, full)Source

The equivalent of span (not . f)

group :: (ListLike full' full, Eq item) => full -> full'Source

Split a list into sublists, each which contains equal arguments. For order-preserving types, concatenating these sublists will produce the original list. See also groupBy.

inits :: ListLike full' full => full -> full'Source

All initial segments of the list, shortest first

tails :: ListLike full' full => full -> full'Source

All final segnemts, longest first

isPrefixOf :: Eq item => full -> full -> BoolSource

True when the first list is at the beginning of the second.

isSuffixOf :: Eq item => full -> full -> BoolSource

True when the first list is at the beginning of the second.

isInfixOf :: Eq item => full -> full -> BoolSource

True when the first list is wholly containted within the second

elem :: Eq item => item -> full -> BoolSource

True if the item occurs in the list

notElem :: Eq item => item -> full -> BoolSource

True if the item does not occur in the list

find :: (item -> Bool) -> full -> Maybe itemSource

Take a function and return the first matching element, or Nothing if there is no such element.

filter :: (item -> Bool) -> full -> fullSource

Returns only the elements that satisfy the function.

partition :: (item -> Bool) -> full -> (full, full)Source

Returns the lists that do and do not satisfy the function. Same as (filter p xs, filter (not . p) xs)

index :: full -> Int -> itemSource

The element at 0-based index i. Raises an exception if i is out of bounds. Like (!!) for lists.

elemIndex :: Eq item => item -> full -> Maybe IntSource

Returns the index of the element, if it exists.

elemIndices :: (Eq item, ListLike result Int) => item -> full -> resultSource

Returns the indices of the matching elements. See also findIndices

findIndex :: (item -> Bool) -> full -> Maybe IntSource

Take a function and return the index of the first matching element, or Nothing if no element matches

findIndices :: ListLike result Int => (item -> Bool) -> full -> resultSource

Returns the indices of all elements satisfying the function

sequence :: (Monad m, ListLike fullinp (m item)) => fullinp -> m fullSource

Evaluate each action in the sequence and collect the results

mapM :: (Monad m, ListLike full' item') => (item -> m item') -> full -> m full'Source

A map in monad space. Same as sequence . map

See also rigidMapM

rigidMapM :: Monad m => (item -> m item) -> full -> m fullSource

Like mapM, but without the possibility of changing the type of the item. This can have performance benefits with some types.

nub :: Eq item => full -> fullSource

Removes duplicate elements from the list. See also nubBy

delete :: Eq item => item -> full -> fullSource

Removes the first instance of the element from the list. See also deleteBy

deleteFirsts :: Eq item => full -> full -> fullSource

List difference. Removes from the first list the first instance of each element of the second list. See '(\)' and deleteFirstsBy

union :: Eq item => full -> full -> fullSource

List union: the set of elements that occur in either list. Duplicate elements in the first list will remain duplicate. See also unionBy.

intersect :: Eq item => full -> full -> fullSource

List intersection: the set of elements that occur in both lists. See also intersectBy

sort :: Ord item => full -> fullSource

Sorts the list. On data types that do not preserve ordering, or enforce their own ordering, the result may not be what you expect. See also sortBy.

insert :: Ord item => item -> full -> fullSource

Inserts the element at the last place where it is still less than or equal to the next element. On data types that do not preserve ordering, or enforce their own ordering, the result may not be what you expect. On types such as maps, this may result in changing an existing item. See also insertBy.

toList :: full -> [item]Source

Converts the structure to a list. This is logically equivolent to fromListLike, but may have a more optimized implementation.

fromList :: [item] -> fullSource

Generates the structure from a list.

fromListLike :: ListLike full' item => full -> full'Source

Converts one ListLike to another. See also toList. Default implementation is fromListLike = map id

nubBy :: (item -> item -> Bool) -> full -> fullSource

Generic version of nub

deleteBy :: (item -> item -> Bool) -> item -> full -> fullSource

Generic version of deleteBy

deleteFirstsBy :: (item -> item -> Bool) -> full -> full -> fullSource

Generic version of deleteFirsts

unionBy :: (item -> item -> Bool) -> full -> full -> fullSource

Generic version of union

intersectBy :: (item -> item -> Bool) -> full -> full -> fullSource

Generic version of intersect

groupBy :: (ListLike full' full, Eq item) => (item -> item -> Bool) -> full -> full'Source

Generic version of group.

sortBy :: (item -> item -> Ordering) -> full -> fullSource

Sort function taking a custom comparison function

insertBy :: (item -> item -> Ordering) -> item -> full -> fullSource

Like insert, but with a custom comparison function

genericLength :: Num a => full -> aSource

Length of the list

genericTake :: Integral a => a -> full -> fullSource

Generic version of take

genericDrop :: Integral a => a -> full -> fullSource

Generic version of drop

genericSplitAt :: Integral a => a -> full -> (full, full)Source

Generic version of splitAt

genericReplicate :: Integral a => a -> item -> fullSource

Generic version of replicate

Instances

The FoldableLL class

class FoldableLL full item | full -> item whereSource

This is the primary class for structures that are to be considered foldable. A minimum complete definition provides foldl and foldr.

Instances of FoldableLL can be folded, and can be many and varied.

These functions are used heavily in Data.ListLike.

Methods

foldl :: (a -> item -> a) -> a -> full -> aSource

Left-associative fold

foldl' :: (a -> item -> a) -> a -> full -> aSource

Strict version of foldl.

foldl1 :: (item -> item -> item) -> full -> itemSource

A variant of foldl with no base case. Requires at least 1 list element.

foldr :: (item -> b -> b) -> b -> full -> bSource

Right-associative fold

foldr' :: (item -> b -> b) -> b -> full -> bSource

Strict version of foldr

foldr1 :: (item -> item -> item) -> full -> itemSource

Like foldr, but with no starting value

Instances

The StringLike class

class StringLike s whereSource

An extension to ListLike for those data types that are similar to a String. Minimal complete definition is toString and fromString.

Methods

toString :: s -> StringSource

Converts the structure to a String

fromString :: String -> sSource

Converts a String to a list

lines :: ListLike full s => s -> fullSource

Breaks a string into a list of strings

words :: ListLike full s => s -> fullSource

Breaks a string into a list of words

Instances

The InfiniteListLike class

class ListLike full item => InfiniteListLike full item | full -> item whereSource

An extension to ListLike for those data types that are capable of dealing with infinite lists. Some ListLike functions are capable of working with finite or infinite lists. The functions here require infinite list capability in order to work at all.

Methods

iterate :: (item -> item) -> item -> fullSource

An infinite list of repeated calls of the function to args

repeat :: item -> fullSource

An infinite list where each element is the same

cycle :: full -> fullSource

Converts a finite list into a circular one

Instances

ListLike [a] a => InfiniteListLike [a] a