Haskell

[michelk]

Added support for haskell as foreign language (#312)

[yihui]

Awesome. Thanks!

[yihui]

BTW, may I have your name added to DESCRIPTION? https://github.com/yihui/knitr/blob/master/DESCRIPTION

[michelk]

Off course, thanks

[yihui]

hi @michelk, is it possible to write the code into a file and run ghc on the file? I mean like a shell script sh foo.sh; I tried ghc foo.hs using your example [x | x <- [1..10], odd x] but it does not work; I know little about haskell, so your help is appreciated :)

[michelk]

hi @yihui,
I admit, Haskell support in knitr is a bit tricky; in org-mode ob-haskell.el they write

Org-Babel support for evaluating haskell source code. This one will
be sort of tricky because haskell programs must be compiled before
they can be run, but haskell code can also be run through an
interactive interpreter.

For now lets only allow evaluation using the haskell interpreter.

Unlike R, in Haskell you couldn't just copy-paste between script and interpreter.

The following works for the interpreter:

• single expression: ghc -e "[x | x <- [3..10], odd x]"
• multi-line: ghc -e "let x = 5" -e "3*x"
• using the interpreter directly: echo "[x | x <- [2..10], odd x]" | ghci

Compilation is more tricky and hard generalize; the corresponding
Haskell-program would look like

echo "main = putStrLn . unwords $ [show x | x <- [2..10], odd x]" > tmp.hs

runhaskell tmp.hs

or

ghc --make tmp.hs && ./tmp

Currently in org-mode as in knitr, you have to write code as you were in
ghci. And, as I remember, multi-line expressions in knitr are right now not
supported.

[yihui]

I see. Thanks for the explanation. I'll add multiline support soon.