Is START_FILE a GHC pragma?

Question

Who could provide information regarding START_FILE pragma?

The is no word about START_FILE in GHC Pragmas Documentation . Nevertheless it seems to be widely used [1] , [2] , [3] .

Unfortunately ghc 8.2.2 does not compile following code [1] .

{-# START_FILE main.hs #-}
main = readFile "file.txt" >>= putStr

{-# START_FILE file.txt #-}
Hello, world!

Answer 1

No, this is an extension specific to School of Haskell Markdown . It's used to provide several "files" in a single Markdown code block.

It's not "widely used" outside of School of Haskell for that reason. When reading such code snippets, simple treat everything after a START_FILE pragma as if it was in a file with the name indicated as the parameter (if it indicates a format like BASE64 you need to put the decoded bytes into the file instead).

Answer 2

This pragma is used by stack templates. You can specify multiple files inside single file with extension .hsfiles by separating files with {-# START_FILE #-} pragma.

stack new PACKAGE_NAME myfiles.hsfiles will create those files (and all directories automatically) according to your layout, if myfiles.hsfiles contains:

{-# START_FILE {{name}}.cabal #-}
name:                {{name}}
version:             0.1.0.0

or

{-# START_FILE package.yaml #-}
name:                {{name}}
version:             0.1.0.0

See some examples in this repository:

• https://github.com/commercialhaskell/stack-templates