Haskell code blocks and examples with output

[lambdacalculator]

Have executable Haskell code blocks been implemented anywhere? In general, what approach do writers of Haskell tutorials/books take to include code examples with automatically generated output (say from ghci)? What if library imports are needed to produce the output?

[mcanouil]

The knitr engine supports Haskell.

---
engine: knitr
---

```{haskell}
code
```