diff options
| -rw-r--r-- | ghc/docs/users_guide/vs_haskell.sgml | 93 |
1 files changed, 87 insertions, 6 deletions
diff --git a/ghc/docs/users_guide/vs_haskell.sgml b/ghc/docs/users_guide/vs_haskell.sgml index 38d1472b4b..8c1e7af6ae 100644 --- a/ghc/docs/users_guide/vs_haskell.sgml +++ b/ghc/docs/users_guide/vs_haskell.sgml @@ -19,6 +19,75 @@ phenomena. The limitations here are listed in Haskell-Report order (roughly). </Para> + <sect2 id="infelicities-lexical"> + <title>Lexical syntax</title> + + <itemizedlist> + <listitem> + <para>The Haskell report specifies that programs may be + written using Unicode. GHC only accepts the ISO-8879-1 + character set at the moment.</para> + </listitem> + + <listitem> + <para>Certain lexical rules regarding qualified identifiers + are slightly different in GHC compared to the Haskell report. + When you have + <replaceable>module</replaceable><literal>.</literal><replaceable>reservedop</replaceable>, + such as <literal>M.\</literal>, GHC will interpret it as a + single qualified operator rather than the two lexemes + <literal>M</literal> and <literal>.\</literal>.</para> + </listitem> + </itemizedlist> + </sect2> + + <sect2 id="infelicities-syntax"> + <title>Context-free syntax</title> + + <itemizedlist> + <listitem> + <para>GHC doesn't do fixity resolution on the left hand side + of a binding before deciding which symbol is the function + symbol. For example, the following fails, because GHC makes + the assumption that the function symbol is + <literal>|-</literal>:</para> +<programlisting> +infix 5 |- +infix 9 := + +data Equal = Char := Int + +0 |- x:=y = 1 |- x:=y -- XXX fails here +</programlisting> + </listitem> + + <listitem> + <para>GHC doesn't do fixity resolution in expressions during + parsing. For example, according to the Haskell report, the + following expression is legal Haskell: +<programlisting> + let x = 42 in x == 42 == True +</programlisting> + and parses as: +<programlisting> + (let x = 42 in x == 42) == True +</programlisting> + because according to the report, the <literal>let</literal> + expression <quote>extends as far to the right as + possible</quote>. Since it can't extend past the second + equals sign without causing a parse error + (<literal>==</literal> is non-fix), the + <literal>let</literal>-expression must terminate there. GHC + simply gobbles up the whole expression, parsing like this: +<programlisting> + (let x = 42 in x == 42 == True) +</programlisting> + The Haskell report is arguably wrong here, but nevertheless + it's a difference between GHC & Haskell 98.</para> + </listitem> + </itemizedlist> + </sect2> + <Sect2 id="infelicities-exprs-pats"> <Title>Expressions and patterns </Title> @@ -140,16 +209,28 @@ main = print (array (1,1) [(1,2), (1,3)]) <Para> <VariableList> + <varlistentry> + <term>The <literal>Char</literal> type</term> + <indexterm><primary><literal>Char</literal></primary><secondary>size + of</secondary></indexterm> + <listitem> + <para>The Haskell report says that the + <literal>Char</literal> type holds 16 bits. GHC follows + the ISO-10646 standard a little more closely: + <literal>maxBound :: Char</literal> in GHC is + <literal>0x10FFFF</literal>.</para> + </listitem> + </varlistentry> + <VarListEntry> <Term>Arbitrary-sized tuples:</Term> <ListItem> <Para> -Plain old tuples of arbitrary size <Emphasis>do</Emphasis> work. -</Para> - -<Para> -HOWEVER: standard instances for tuples (<Literal>Eq</Literal>, <Literal>Ord</Literal>, <Literal>Bounded</Literal>, <Literal>Ix</Literal> -<Literal>Read</Literal>, and <Literal>Show</Literal>) are available <Emphasis>only</Emphasis> up to 5-tuples. +Tuples are currently limited to size 61. HOWEVER: standard instances +for tuples (<Literal>Eq</Literal>, <Literal>Ord</Literal>, +<Literal>Bounded</Literal>, <Literal>Ix</Literal> +<Literal>Read</Literal>, and <Literal>Show</Literal>) are available +<Emphasis>only</Emphasis> up to 5-tuples. </Para> <Para> |