Hugs (interpreter)
| Developer(s) | Mark P. Jones, others |
|---|---|
| Stable release | September 2006
/ September 21, 2006 |
| Operating system | Cross-platform |
| Type | Compiler |
| License | BSD |
| Website | Hugs 98 homepage |
Hugs (Haskell User's Gofer System), also Hugs 98, is a bytecode interpreter for the functional programming language Haskell. Hugs is the successor to Gofer, and was originally derived from Gofer version 2.30b.[2] Hugs and Gofer were originally developed by Mark P. Jones, now a professor at Portland State University.
Hugs comes with a simple graphics library. As a complete Haskell implementation that is portable and simple to install, Hugs is sometimes recommended for new Haskell users.
Hugs deviates from the Haskell 98 specification[3] in several minor ways.[4] For example, Hugs does not support mutually recursive modules. A list of differences exists.[5]
The Hugs prompt (a Haskell REPL) accepts expressions for evaluation, but not module, type or function definitions. Hugs can load Haskell modules at start-up.[6]
Examples
Extensible records
An example of "Typed records with extensibility", a non standard feature unique to Hugs.[7]
module Main where
import Hugs.Trex
type Coord = Double
type Point2D = Rec (x::Coord, y::Coord)
type Point3D = Rec (x::Coord, y::Coord, z::Coord)
point2D = (x=1, y=1) :: Point2D
-- emptyRec :: Rec EmptyRow -- predefined
-- (x=1 | (y=1)) -- rec. extension
-- (x=v | rec) -- record value decomposition, pattern fields must be non empty
-- (x::type | rec) -- record type decomposition
-- (rec\z) in the context means ''rec'' does not contain field ''z''
-- add a field z with the same type as field x
addZCoord :: (r\z, r\x) => t -> Rec ( x::t | r) -> Rec ( x::t, z::t | r)
addZCoord z ( x = x | other) = (x = x, z = z | other)
point3D = addZCoord 3 point2D -- :: Point3D
-- admit any record with ''showable'' fields x and y
printXY :: (Show t, r\x, r\y) => Rec (x::t, y::t | r) -> IO ()
printXY point = putStrLn xy
-- with SML style field accessors ('#' prefix)
where xy = show (#x point) ++", "++ show (#y point)
incrementX :: (Num t, r\x) => Rec (x::t | r) -> Rec (x::t | r)
incrementX (x=v | rest) = (x=v+1 | rest)
main = do
let point3D' = incrementX point3D
printXY point2D
printXY point3D'
Running with H98 compatibility turned off to activate language extensions:[8]
runhugs -98 test.hs
References
- ^ "Hugs 98". www.haskell.org.
- ^ "Frequently Asked Questions about Hugs". Retrieved 2006-08-04.
- ^ Simon Peyton Jones (editor) (December 2002). "Haskell 98 Language and Libraries: The Revised Report". Retrieved 2006-08-03.
{{cite web}}:|author=has generic name (help) - ^ "Haskell 98 non-compliance". The Hugs 98 User's Guide. Retrieved 2006-08-04.
- ^ "List of differences with H98 standard".
- ^ "Loading and editing Haskell module files". The Hugs 98 User's Guide. Retrieved 2006-08-04.
- ^ "Hugs-specific language extensions". www.haskell.org.
- ^ "Changing the behaviour of Hugs". www.haskell.org.