Haskell stack command line flag for executing an expression

Question

If I have a simple Haskell one-liner, what's the flag in ghc or ghci that could execute this from the command line?

I'm looking for something like:

stack ghci -e 'putStrLn "hello world"'

Similar to

$ R --quiet -e "cat('hello world')"
> cat('hello world')
hello world>

or

$ python -c "print('hello world')"
hello world

Edit for 'ghci -e' debug

(This question is resolved with an excellent answer already, but just debugging that the flag seems like it /should/ work above...)

Weirdly couldn't get the seemingly supported ghci -e working for me. Testing it is not just my machine, I also ran this on Ubuntu and had the same issue:

FROM ubuntu:18.04
ENV DEBIAN_FRONTEND=noninteractive

RUN apt-get update \
 && apt-get install  --yes curl \   
 && curl -sSL https://get.haskellstack.org/ | sh \
 && export HOME=/root/.local/bin:$HOME \
 && stack ghci -e 'putStrLn "hello world"'

Then

$ docker build .

Produced...

Stack has been installed to: /usr/local/bin/stack

WARNING: '/root/.local/bin' is not on your PATH.
    For best results, please add it to the beginning of PATH in your profile.

Invalid option `-e'

Usage: stack ghci [TARGET/FILE] [--ghci-options OPTIONS] [--ghc-options OPTIONS]
                  [--flag PACKAGE:[-]FLAG] [--with-ghc GHC] [--[no-]load]
                  [--package ARG] [--main-is TARGET] [--load-local-deps]
                  [--[no-]package-hiding] [--only-main] [--trace] [--profile]
                  [--no-strip] [--[no-]test] [--[no-]bench] [--help]
  Run ghci in the context of package(s) (experimental)
The command '/bin/sh -c apt-get update  && apt-get install  --yes curl  && curl -sSL https://get.haskellstack.org/ | sh  && export HOME=/root/.local/bin:$HOME  && stack ghci -e 'putStrLn "hello world"'' returned a non-zero code: 1

stack eval 'putStrLn "hello world"'

Redu
– Redu

2018-11-25 19:02:50 +00:00
Commented Nov 25, 2018 at 19:02 — Redu
– Redu, Commented Nov 25, 2018 at 19:02
@Redu, this works, can you post as an answer I can accept?

Mittenchops
– Mittenchops

2018-11-25 19:06:31 +00:00
Commented Nov 25, 2018 at 19:06 — Mittenchops
– Mittenchops, Commented Nov 25, 2018 at 19:06

Redu · Accepted Answer · 2018-11-25 19:12:24Z

7

If you check $ stack --help at one point you see that

eval                     Evaluate some haskell code inline. Shortcut for
                         'stack exec ghc -- -e CODE'

So instead of doing like

$ stack exec ghc -- -e 'putStrLn "hello world"'
hello world

you may do like

$ stack eval 'putStrLn "hello world"'
hello world

answered Nov 25, 2018 at 19:12

Redu

26.3k6 gold badges61 silver badges84 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

willeM_ Van Onsem · Accepted Answer · 2018-11-25 19:08:06Z

2

In fact you already have this flag: it is just:

-e expr
Evaluate expr; see eval-mode for details

So you can write it like:

ghci -e 'putStrLn "hello world"'

In fact if you use stack ghci, you just open ghci with your application, but the -e flag is not "stack-specific".

For example:

$ ghci -e 'putStrLn "hello world"'
hello world

edited Nov 25, 2018 at 19:08

answered Nov 25, 2018 at 19:04

willeM_ Van Onsem

482k33 gold badges483 silver badges624 bronze badges

6 Comments

Mittenchops Over a year ago

Hmm, I get: $ stack ghci -e 'putStrLn "hello world"' Invalid option -e' ` And don't otherwise have ghc installed outside of stack, if possible to keep it that way: $ ghc -e 'putStrLn "hello world"' Command 'ghc' not found, but can be installed with: sudo apt install ghc

willeM_ Van Onsem Over a year ago

@Mittenchops: what version of ghci do you use? This is already supported since 7.6 (or even eariler) iirc.

Mittenchops Over a year ago

$ stack ghci Configuring GHCi with the following packages:  GHCi, version 8.4.3: http://www.haskell.org/ghc/  :? for help

willeM_ Van Onsem Over a year ago

@Mittenchops: in 8.4.3, this flag is also supported: downloads.haskell.org/~ghc/8.4.3/docs/html/users_guide/…, strange

willeM_ Van Onsem Over a year ago

@Mittenchops: well I work with Ubuntu as well, so this makes it even more strange :S

|

Collectives™ on Stack Overflow

Haskell stack command line flag for executing an expression

Edit for 'ghci -e' debug

2 Answers 2

Comments

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

Edit for 'ghci -e' debug

2 Answers 2

Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related