1. Art and Diseño

Haskell in the Software
Industry
What is Haskell?
Haskell in a nutshell
Haskell is a pure, non-strict, statically typed, garbage collected, general purpose, functional
programming language.
Early history
➞
Growing interest towards lazy languages in the late 70s and early 80s led to the creation
of several academic languages.
➞
Haskell was designed by a committee of researchers to combine the best features from
the existing lazy languages.
The escape from the Ivory Tower
➞
Haskell stayed relatively unknown outside research circles until at least early 2000s.
➞
Uncertain what caused the sudden growth of interest, but can be partly attributed to the
combination of
1
The Haskell standard reaching maturity with the revised edition of The Haskell
Language Report ‘98
2
The Haskell library ecosystem having a critical mass of high quality libraries for real
applications
3
The global resurgence of interest towards the functional paradigm in general
Standard versus Implementation
➞
Standard Haskell is defined in The Haskell Language Report
➞
Some library authors like to ensure that their can be compiled with any compliant
compiler.
➞
However, almost all real-world development of Haskell is done using GHC.
➞
It is common in application development to target GHC exclusively and take advantage of
all it’s non-standard extensions.
➞
Some companies even maintain their custom, in-house Haskell compiler optimized for
their specific use-case.
What makes Haskell
relevant for today’s
software industry?
What is Haskell best suited for?
➞
Parsing and transforming data
➞
Creating custom DSL to express complicated business logic or rules
➞
Business domains where software reliability is a high priority
Haskell’s selling points for the software industry
➞
Increased productivity
➞
Less bugs
➞
Less code
➞
Simpler software architecture
➞
Easier parallelism and concurrency
➞
Performance between “pretty good” and great*
What is Haskell used for in the
industry?
➞
Facebook uses Haskell as part of their infrastructure
●
HAXL: a parallel, data-query DSL
➞
Banks and other financial institutions commonly use Haskell, OCaml or Erlang
➞
Used for embedded, hard real-time systems as a DSL to generate statically checked, lowlevel C-code
➞
https://www.haskell.org/haskellwiki/Haskell_in_industry
What is Haskell used for at Leonidas?
➞
The use of Haskell in real projects is still pretty limited: so far we’ve done two small
production projects and one medium sized project in addition to one-off “scripting” tasks
➞
Even outside production use, Haskell is useful for exploring ideas around functional
programming and teaching functional concepts
➞
We’ve organized a semi-regular event called “The Lambda Saturday” where people can
discuss and learn about Haskell and functional programming
What makes Haskell
different?
How does programming Haskell differ from imperative
programming?
➞
Lack of control structures
➞
No mutable variables
➞
Mostly immutable data structures
How does Haskell differ from other functional languages?
➞
Syntax
➞
Purity
➞
Immutability
➞
Non-nullability as a default
➞
Type-system
➞
Full type-inference
➞
Access to low-level operations and C FFI
What are the downsides
of using Haskell?
Compiling to native binaries
➞
Deploying native binaries somewhat problematic compared to VM languages
➞
Need to use a cross-compiler or a build server whose operating system matches the
target machine
➞
In practice, this can be automated but needs to be taken into account
Difficulties in predicting memory and performance
characteristics
➞
Haskell code can achieve extremely good performance, but only in the hands of a very
experienced Haskell programmer.
➞
With less experience, it’s easy to write code that has quadratic or exponential complexity
or which quickly leaks memory due to incorrect use of laziness.
➞
The Haskell ecosystem does provide tools to tackle these issues, but it’s a genuine
problem when starting out.
Issues with dependency management
➞
I.e. the “cabal hell”
➞
When two libraries B and C both depend on library A and
you are developing application D, it’s possible to have a
situation where B and C are linked against two different
versions of A.
➞
Can be mitigated with sandboxes but there’s no perfect
solution (as of yet).
High learning curve
➞
It takes significantly longer to become productive in Haskell
●
➞
Haskell is very unique compared to commonly used programming languges
●
➞
Pair-programming with an expert Haskeller helps
Requires unlearning old habits
The academic roots of Haskell still show through
●
Many abstractions, libraries and terminology based on category theory and other
branches of abstract mathematics
●
Lot of valuable learning material is in the form of research papers
Questions?