CODEWITHSUNDEEP
haskellhaskell-stack
Mittenchops
Mittenchops

Reputation: 19664

Haskell stack command line flag for executing an expression

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

Upvotes: 1

Views: 458

Answers (2)

Redu
Redu

Reputation: 26161

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

Upvotes: 7

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476554

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

Upvotes: 2

Related Questions