nextcloud-docs/haskell/content.md

What is Haskell?

Haskell is a lazy, functional, statically-typed programming language with advanced type system features such as higher-rank, higher-kinded parametric polymorphism, monadic effects, generalized algebraic data types (GADTs), flexible type classes, associated type families, and more.

Haskell's ghc is a portable, optimizing compiler with a foreign-function interface (FFI), an LLVM backend, and sophisticated runtime support for concurrency, explicit/implicit parallelism, runtime profiling, etc. Other Haskell tools like criterion, quickcheck, hpc, and haddock provide advanced benchmarking, property-based testing, code coverage, and documentation generation.

A large number of production-quality Haskell libraries are available from Hackage. The cabal tool fetches packages and builds projects using the Hackage ecosystem.

%%LOGO%%

About this image

This image ships a minimal Haskell toolchain with the following packages:

• ghc
• alex
• cabal-install
• happy

How to use this image

Start an interactive interpreter session with ghci:

$ docker run -it --rm haskell:7.8
GHCi, version 7.8.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude>

Dockerize a Hackage app with a Dockerfile inheriting from the base image:

FROM haskell:7.8
RUN cabal update && cabal install MazesOfMonad
VOLUME /root/.MazesOfMonad
ENTRYPOINT ["/root/.cabal/bin/mazesofmonad"]

Iteratively develop then ship a Haskell app with a Dockerfile utilizing the build cache:

FROM haskell:7.8

RUN cabal update

# Add .cabal file
ADD ./server/snap-example.cabal /opt/server/snap-example.cabal

# Docker will cache this command as a layer, freeing us up to
# modify source code without re-installing dependencies
RUN cd /opt/server && cabal install --only-dependencies -j4

# Add and Install Application Code
ADD ./server /opt/server
RUN cd /opt/server && cabal install

# Add installed cabal executables to PATH
ENV PATH /root/.cabal/bin:$PATH

# Default Command for Container
WORKDIR /opt/server
CMD ["snap-example"]

Examples

See the application snippet above in more detail in the example snap application.