<xref linkend="book-hslibs">.
</Para>
-<Sect1 id="language-options">
-<Title>Language variations
-</Title>
-
-<Para> There are several flags that control what variation of the language are permitted.
-Leaving out all of them gives you standard Haskell 98.</Para>
-
-<VariableList>
-
-<VarListEntry>
-<Term><Option>-fglasgow-exts</Option>:</Term>
-<ListItem>
-<Para>This simultaneously enables all of the extensions to Haskell 98 described in this
-chapter, except where otherwise noted. </Para>
-</ListItem> </VarListEntry>
-
-<VarListEntry>
-<Term><Option>-fno-monomorphism-restriction</Option>:</Term>
-<ListItem>
-<Para> Switch off the Haskell 98 monomorphism restriction. Independent of the <Option>-fglasgow-exts</Option>
-flag. </Para>
-</ListItem> </VarListEntry>
-
-<VarListEntry>
-<Term><Option>-fallow-overlapping-instances</Option>,
- <Option>-fallow-undecidable-instances</Option>,
- <Option>-fcontext-stack</Option>:</Term>
-<ListItem>
-<Para> See <XRef LinkEnd="instance-decls">.
-Only relevant if you also use <Option>-fglasgow-exts</Option>.
-</Para>
-</ListItem> </VarListEntry>
-
-<VarListEntry>
-<Term><Option>-fignore-asserts</Option>:</Term>
-<ListItem>
-<Para> See <XRef LinkEnd="sec-assertions">.
-Only relevant if you also use <Option>-fglasgow-exts</Option>.
-</Para>
-</ListItem> </VarListEntry>
-
-<VarListEntry>
-<Term> <Option>-finline-phase</Option>:</Term>
-<ListItem>
-<Para> See <XRef LinkEnd="rewrite-rules">.
-Only relevant if you also use <Option>-fglasgow-exts</Option>.</para>
-</ListItem> </VarListEntry>
+ <sect1 id="options-language">
+ <title>Language options</title>
+
+ <indexterm><primary>language</primary><secondary>option</secondary>
+ </indexterm>
+ <indexterm><primary>options</primary><secondary>language</secondary>
+ </indexterm>
+ <indexterm><primary>extensions</primary><secondary>options controlling</secondary>
+ </indexterm>
+
+ <para> These flags control what variation of the language are
+ permitted. Leaving out all of them gives you standard Haskell
+ 98.</Para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term><option>-fglasgow-exts</option>:</term>
+ <indexterm><primary><option>-fglasgow-exts</option></primary></indexterm>
+ <listitem>
+ <para>This simultaneously enables all of the extensions to
+ Haskell 98 described in <xref
+ linkend="ghc-language-features">, except where otherwise
+ noted. </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-fno-monomorphism-restriction</option>:</term>
+ <indexterm><primary><option>-fno-monomorphism-restriction</option></primary></indexterm>
+ <listitem>
+ <para> Switch off the Haskell 98 monomorphism restriction.
+ Independent of the <Option>-fglasgow-exts</Option>
+ flag. </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-fallow-overlapping-instances</option></term>
+ <term><option>-fallow-undecidable-instances</option></term>
+ <term><option>-fcontext-stack</option></term>
+ <indexterm><primary><option>-fallow-overlapping-instances</option></primary></indexterm>
+ <indexterm><primary><option>-fallow-undecidable-instances</option></primary></indexterm>
+ <indexterm><primary><option>-fcontext-stack</option></primary></indexterm>
+ <listitem>
+ <para> See <XRef LinkEnd="instance-decls">. Only relevant
+ if you also use <option>-fglasgow-exts</option>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-fignore-asserts</option>:</term>
+ <indexterm><primary><option>-fignore-asserts</option></primary></indexterm>
+ <listitem>
+ <para>See <XRef LinkEnd="sec-assertions">. Only relevant if
+ you also use <option>-fglasgow-exts</option>.</Para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-finline-phase</option></term>
+ <indexterm><primary><option>-finline-phase</option></primary></indexterm>
+ <listitem>
+ <para>See <XRef LinkEnd="rewrite-rules">. Only relevant if
+ you also use <Option>-fglasgow-exts</Option>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-fgenerics</option></term>
+ <indexterm><primary><option>-fgenerics</option></primary></indexterm>
+ <listitem>
+ <para>See <XRef LinkEnd="generic-classes">. Independent of
+ <Option>-fglasgow-exts</Option>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-fno-implicit-prelude</option></term>
+ <listitem>
+ <para><indexterm><primary>-fno-implicit-prelude
+ option</primary></indexterm> GHC normally imports
+ <filename>Prelude.hi</filename> files for you. If you'd
+ rather it didn't, then give it a
+ <option>-fno-implicit-prelude</option> option. The idea
+ is that you can then import a Prelude of your own. (But
+ don't call it <literal>Prelude</literal>; the Haskell
+ module namespace is flat, and you must not conflict with
+ any Prelude module.)</para>
+
+ <para>Even though you have not imported the Prelude, all
+ the built-in syntax still refers to the built-in Haskell
+ Prelude types and values, as specified by the Haskell
+ Report. For example, the type <literal>[Int]</literal>
+ still means <literal>Prelude.[] Int</literal>; tuples
+ continue to refer to the standard Prelude tuples; the
+ translation for list comprehensions continues to use
+ <literal>Prelude.map</literal> etc.</para>
+
+ <para> With one group of exceptions! You may want to
+ define your own numeric class hierarchy. It completely
+ defeats that purpose if the literal "1" means
+ "<literal>Prelude.fromInteger 1</literal>", which is what
+ the Haskell Report specifies. So the
+ <option>-fno-implicit-prelude</option> flag causes the
+ following pieces of built-in syntax to refer to whatever
+ is in scope, not the Prelude versions:</para>
+
+ <itemizedlist>
+ <listitem>
+ <para>Integer and fractional literals mean
+ "<literal>fromInteger 1</literal>" and
+ "<literal>fromRational 3.2</literal>", not the
+ Prelude-qualified versions; both in expressions and in
+ patterns.</para>
+ </listitem>
+
+ <listitem>
+ <para>Negation (e.g. "<literal>- (f x)</literal>")
+ means "<literal>negate (f x)</literal>" (not
+ <literal>Prelude.negate</literal>).</para>
+ </listitem>
+
+ <listitem>
+ <para>In an n+k pattern, the standard Prelude
+ <literal>Ord</literal> class is used for comparison,
+ but the necessary subtraction uses whatever
+ "<literal>(-)</literal>" is in scope (not
+ "<literal>Prelude.(-)</literal>").</para>
+ </listitem>
+ </itemizedlist>
-<VarListEntry>
-<Term> <Option>-fgenerics</Option>:</Term>
-<ListItem>
-<Para> See <XRef LinkEnd="generic-classes">.
-Independent of <Option>-fglasgow-exts</Option>.
-</Para>
-</ListItem> </VarListEntry>
+ </listitem>
+ </varlistentry>
-</VariableList>
+ </variablelist>
</sect1>
<Sect1 id="primitives">
This restriction is an implementation restriction: we just havn't got around to
implementing the necessary bidirectional maps over arbitrary type constructors.
It would be relatively easy to add specific type constructors, such as Maybe and list,
-to the ones that are allowed.
+to the ones that are allowed.</para>
</ListItem>
<ListItem>
projects / ghc-hetmet.git / blobdiff