CODEWITHSUNDEEP
haskellcommand-line
amindfv
amindfv

Reputation: 8448

GHCi instructions from the command line

In the shell you can string commands together, separated by a semicolon:

cd ../haskell; rm ./foo; ghc foo.hs; cd ../original_directory

It would be great if you could do a similar thing for command-line arguments for ghci, e.g.

ghci Foo.hs; a <- getFoo; print a

Is this possible?

Upvotes: 4

Views: 455

Answers (2)

Daniel Wagner
Daniel Wagner

Reputation: 153172

You can use ghc -e for this:

sorghum:~/programming% cat test.hs
getFoo = getLine
sorghum:~/programming% ghc test.hs -e 'do { a <- getFoo; print a }'
oenuth
"oenuth"

Upvotes: 7

leftaroundabout
leftaroundabout

Reputation: 120741

You can run ghci in silent mode and pass the instructions in through its standard input:

$ cat > ghciPipeTest.hs
getFoo = return 37 :: IO Int
$ ghci -v0 ghciPipeTest.hs <<< ' getFoo >>= print '
37
$

or

$ ghci -v0 ghciPipeTest.hs <<< $' a <- getFoo \n print a '

(assuming you use a bash-like shell. It also works with actual newlines inside the quotes)

Of course, it also works in non-silent mode, the output just looks a bit strange:

$ ghci ghciPipeTest.hs <<< $' a<-getFoo \n print a '
GHCi, version 7.4.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main ( ghciPipeTest.hs, interpreted )
Ok, modules loaded: Main.
*Main> *Main> 37
*Main> Leaving GHCi.

Upvotes: 3

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