Difference between revisions of "No import of Prelude"

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(from Haskell-Cafe)
 
(difference between the methods)
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to the top of the module, or equivalently compile with <code>-fno-implicit-prelude</code> option.
 
to the top of the module, or equivalently compile with <code>-fno-implicit-prelude</code> option.
   
<hask>import Prelude()<hask> is less aggressive than <code>NoImplicitPrelude</code>.
+
<hask>import Prelude()</hask> is less aggressive than <code>NoImplicitPrelude</code>.
E.g. with the first method <hask>fromInteger</hask> is still imported. It is silently inserted for number literals.
+
E.g. with the first method some functions are imported which are silently inserted for several syntactic constructs.
  +
A bare untyped integral number is rewritten as <hask>fromIntegral num</hask>
  +
(so its type will be <hask>Num a => a</hask>),
  +
and list generation syntax is rewritten as follows:
  +
<hask>[n..]</hask> <math>\rightarrow</math> <hask>enumFrom</hask>,
  +
<hask>[n..m]</hask> <math>\rightarrow</math> <hask>enumFromTo</hask>,
  +
<hask>[n,o..]</hask> <math>\rightarrow</math> <hask>enumFromThen</hask>,
  +
<hask>[n,o..m]</hask> <math>\rightarrow</math> <hask>enumFromThenTo</hask>.
  +
  +
There are some such for which even <code>-fno-implicit-prelude</code> isn't enough;
  +
I think these are documented in the "bugs" section of the GHC manual.
  +
   
 
== See also ==
 
== See also ==

Revision as of 18:01, 11 January 2008

Question

Is it possible not to load Prelude module when compiling a Haskell module?

Answer

You can either do

import Prelude()

or add

{-# LANGUAGE NoImplicitPrelude #-}

to the top of the module, or equivalently compile with -fno-implicit-prelude option.

import Prelude() is less aggressive than NoImplicitPrelude. E.g. with the first method some functions are imported which are silently inserted for several syntactic constructs. A bare untyped integral number is rewritten as fromIntegral num (so its type will be Num a => a), and list generation syntax is rewritten as follows: [n..] \rightarrow enumFrom, [n..m] \rightarrow enumFromTo, [n,o..] \rightarrow enumFromThen, [n,o..m] \rightarrow enumFromThenTo.

There are some such for which even -fno-implicit-prelude isn't enough; I think these are documented in the "bugs" section of the GHC manual.


See also