71

I have made a file called time.hs. It contains a single function that measures the execution time another function.

Is there a way to import the time.hs file into another Haskell script?

I want something like:

module Main where
import C:\Haskell\time.hs

main = do
    putStrLn "Starting..."
    time $ print answer
    putStrLn "Done."

Where time is defined in the 'time.hs' as:

module time where
Import <necessary modules>

time a = do
start <- getCPUTime
v <- a
end   <- getCPUTime
let diff = (fromIntegral (end - start)) / (10^12)
printf "Computation time: %0.3f sec\n" (diff :: Double)
return v

I don't know how to import or load a separate .hs file. Do I need to compile the time.hs file into a module before importing?

LambdaScientist
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Jonno_FTW
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3 Answers3

66

Time.hs:

module Time where
...

script.hs:

import Time
...

Command line:

ghc --make script.hs
yairchu
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  • I learned the long way that in this example `script.hs` must be in your present working directory. This means you can't do `ghc --make path/to/script.hs`, for example. – Jesse Looney Aug 12 '20 at 22:17
16

If the module Time.hs is located in the same directory as your "main" module, you can simply type:

import Time

It is possible to use a hierarchical structure, so that you can write import Utils.Time. As far as I know, the way you want to do it won't work.

For more information on modules, see here Learn You a Haskell, Making Our Own Modules.

Philippe Fanaro
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Christian
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4

Say I have two files in the same directory: ModuleA.hs and ModuleB.hs.

ModuleA.hs:

module ModuleA where
...

ModuleB.hs:

module ModuleB where

import ModuleA
...

I can do this: 

    ghc -I. --make ModuleB.hs

Note: The module name and the file name must be the same. Otherwise it can't compile. Something like

Could not find module '...'

will occur.

Joshua Grosso Reinstate CMs
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uol3c
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