6  Library overview

All that you need to do to use libraries is to import them using an import declaration. For example:
 module MandlebrotSet where
 import Array
 import Complex
 ...
Of course, this assumes that HUGSPATH has been set to point to the directories where the libraries are stored, and that import chasing is enabled. The default search path includes the directories containing both the standard and unofficial libraries.

6.1  Standard Libraries

6.2  The Hugs-GHC Extension Libraries

The specifications and implementations of all of these libraries are still evolving, and are subject to change.

6.3  Portable Libraries

• ListUtils This module provides list functions that were removed from the Prelude in the move from Haskell 1.2 to Haskell 1.3.
    module ListUtils where
  
    sums, products   :: Num a => [a] -> [a]
    subsequences     :: [a] -> [[a]]
    permutations     :: [a] -> [[a]]
  
• ParseLib This module provides a library of parser combinators, as described in the paper on Monadic Parser Combinators by Graham Hutton and Erik Meijer [MonParse].
• Interact: This library provides facilities for writing simple interactive programs.
    module Interact where
  
    type Interact = String -> String
  
    end                :: Interact
    readChar, peekChar :: Interact -> (Char -> Interact) -> Interact
    pressAnyKey        :: Interact -> Interact
    unreadChar         :: Char -> Interact -> Interact
    writeChar          :: Char -> Interact -> Interact
    writeStr           :: String -> Interact -> Interact
    ringBell           :: Interact -> Interact
    readLine           :: String -> (String -> Interact) -> Interact
  An expression e of type Interact can be executed as a program by evaluating run e.
• AnsiScreen This library defines some basic ANSI escape seqences for terminal control.
    module AnsiScreen where
  
    type Pos  = (Int,Int)
  
    at        :: Pos -> String -> String
    highlight :: String -> String
    goto      :: Int -> Int -> String
    home      :: String
    cls       :: String
  The definitions in this module will need to be adapted to work with terminals that do not support ANSI escape sequences.
• AnsiInteract This library includes both Interact and AnsiScreen, and also contains further support for screen oriented interactive I/O.
    module AnsiInteract(module AnsiInteract,
                        module Interact,
                        module AnsiScreen) where
    import AnsiScreen
    import Interact
  
    clearScreen       :: Interact -> Interact
    writeAt           :: Pos -> String -> Interact -> Interact
    moveTo            :: Pos -> Interact -> Interact
    readAt            :: Pos                  -> -- start coords
                         Int                  -> -- max input length
                         (String -> Interact) -> -- continuation
                         Interact
    defReadAt         :: Pos                  -> -- start coords
                         Int                  -> -- max input length
                         String               -> -- default value
                         (String -> Interact) -> -- continuation
                         Interact
    promptReadAt      :: Pos                  -> -- start coords
                         Int                  -> -- max input length     
                         String               -> -- prompt
                         (String -> Interact) -> -- continuation
                         Interact
    defPromptReadAt   :: Pos                  -> -- start coords
                         Int                  -> -- max input length     
                         String               -> -- prompt
                         String               -> -- default value
                         (String -> Interact) -> -- continuation
                         Interact
  

6.4  Hugs-Specific Libraries

• Number This library defines a numeric datatype of fixed width integers (whatever Int supplies). However, unlike the built-in Int type, overflows are detected and cause a run-time error. To ensure that all integer arithmetic in a given module includes overflow protection you must include a default declaration for Number.
    module Number where
    data Number              -- fixed width integers
    instance Eq       Number -- class instances
    instance Ord      Number
    instance Show     Number
    instance Enum     Number
    instance Num      Number
    instance Bounded  Number
    instance Real     Number
    instance Ix       Number
    instance Integral Number
  This library cannot be used when Hugs is running in Haskell 98 mode because it requires features that are only supported in full Hugs mode.
• IOExtensions This module provides non-standard extensions to the IO monad.
    module IOExtensions where
  
    readBinaryFile     :: FilePath -> IO String
    writeBinaryFile    :: FilePath -> String -> IO ()
    appendBinaryFile   :: FilePath -> String -> IO ()
    openBinaryFile     :: FilePath -> IOMode -> IO Handle
  
    getCh              :: IO Char
    argv               :: [String]
  
• Trace: This library provides a single function, that can sometimes be useful for debugging:
    module Trace where
    trace     :: String -> a -> a
    traceShow :: Show a => String -> a -> a
  When called, trace prints the string in its first argument, and then returns the second argument as its result. The traceShow function is a variant of trace that generates its output message by concatenating the supplied String argument with the result of applying show to its value argument. These functions are not referentially transparent, and should only be used for debugging, or for monitoring execution. You should also be warned that, unless you understand some of the details about the way that Hugs programs are executed, results obtained using trace can be rather confusing. For example, the messages may not appear in the order that you expect. Even ignoring the output that they produce, adding calls to trace can change the semantics of your program. Consider this a warning!
• Trex This library supports Trex extensible records. These can only be used when Hugs is compiled with Trex support using the -enable-TREX configuration option. Trex is described in more details in Section 7.2.
• HugsInternals This library provides primitives for accessing Hugs internals; for example, they provide the means with which to implement simple error-recovery and debugging facilities in Haskell. They should be regarded as an experimental feature and may not be supported in future versions of Hugs. They can only be used if hugs was configured with the --enable-internal-prims flag.
• GenericPrint This library provides a "generic" (or "polymorphic") print function in Haskell, that works in essentially the same way as Hugs' builtin printer when the -u option is used. The module HugsInternals is required.
• CVHAssert This library provides a simple implementation of Cordy Hall's assertions for performance debugging. These primitives are an experimental feature that may be removed in future versions of Hugs. They can only be used if hugs was configured with the --enable-internal-prims flag.
• Win32 This library contains Haskell versions for many of the functions in the Microsoft Win32 library. It is only available on Windows 95/NT. The --with-plugins configuration option must be used in conjunction with this and the other Microsoft libraries.