The ~= operator can be seen as pattern equality. Stealing the ~= operator for the moment, imagine: One extension I often find myself wanting is some kind of "pattern match equality". The reason is that in Haskell pattern matching is used to control program flow, not as an expression. Unfortunately the definition of isStar - something that is conceptually very simple - is rather verbose: Now imagine you want to check that all atoms in a regular expression are Star's. However, there is one operation that I think would be useful - pattern equality. I realise that most people would demand to add higher ranked types and multi-parameter type classes, but the only extension I'm crying out for is pattern guards. Python.Haskell 98 + Hierarchical modules is pretty much feature complete as far as I'm concerned. The syntax for guards is almost identical
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If you don't need the full power of pattern matching and just want a neater Note that if you are using IPython, Hask's Polymorphic, to allow for any operator overloading. List import zipWith, take > take( 5) % zipWith( _ * _, L, L)Īs you can see, this much easier than using List import takeWhile > takeWhile( _ > ( _ + _)( 'Hello ', 'world')ġ024 > from hask. It is also possible to create type synonyms using
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This can lead to shorter, more elegant code in many cases. Unlike many other languages, Haskell gives a lot of flexibility to developers to define custom operators. Print "Launching missiles! Bombs away!" % num_missiles Operator Glossary One aspect of Haskell that many new users find difficult to get a handle on is operators. # type signature for a function that returns nothing sig( H / int > None) def launch_missiles( num_missiles): Return Nothing if y = 0 else Just( x / y) # type signature with a type constructor (Maybe) that has type arguments sig( H / int > int > t( Maybe, int)) def safe_div( x, y): # type signature with an Eq constraint sig( H / "a" > bool) def not_in( y, xs):
# map a typed function over a List sig( H / ( H / "a" > "b") > ) def map( f, xs): # map a Python (untyped) function over a Python (untyped) set sig( H / func > set > set) def set_map( fn, lst): Return x + y # reverse order of arguments to a function sig( H / ( H / "a" > "b" > "c") > "b" > "a" > "c") def flip( f, b, a): # add two ints together sig( H / int > int > int) def add( x, y): Records are an extension of sum algebraic data type that allow fields to be named: data StandardType StandardType String Int Bool -standard. Bang patterns and strict matching do not affect the type system in any way. The latter two extensions are simply a way to avoid littering high-performance code with bang patterns, making it harder to read. Type, a lazy and statically-typed list, similar to Strict pattern ( Strict) makes all patterns and let bindings strict by default, on a per-module basis. I recommend playing around in the REPL while going through the examples. The rest of this README lays out the basics. Hask is a grab-bag of features that add up to one big pseudo-Haskell functional Of this project, abusing the Python language as much as possible is encouraged.
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I wanted to cram as much of Haskell into Python as possible while still beingġ00% compatible with the rest of Python, just to see if any useful ideas cameĬontributions, forks, and extensions to this experiment are always welcome!įeel free to submit a pull request, open an issue, or email me. Note that all of this is still very much pre-alpha, and some things may be buggy! Python port of (some of) the standard libraries from Haskell'sįeatures not yet implemented, but coming soon:īetter support for polymorphic return values/type defaultingīetter support for lazy evaluation (beyond just the Hask is a pure-Python, zero-dependencies library that mimics most of the coreįull Hindley-Milner type system (with typeclasses) that will typecheck anyįunction decorated with a Hask type signatureĮasy creation of new algebraic data types and new typeclasses, withĪutomagical function currying/partial application and function compositionĪll your favorite syntax and control flow tools, including operator sections,
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