No import of Prelude

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Revision as of 18:01, 11 January 2008 by Lemming (talk | contribs) (difference between the methods)
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Is it possible not to load Prelude module when compiling a Haskell module?


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