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>Data.Text.Lazy.Read</TITLE
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>text-0.10.0.0: An efficient packed Unicode text type.</TD
><TD CLASS="topbut"
><A HREF="src/Data-Text-Lazy-Read.html"
>Source code</A
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>Contents</A
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><FONT SIZE="6"
>Data.Text.Lazy.Read</FONT
></TD
><TD ALIGN="right"
><TABLE CLASS="narrow" CELLSPACING="0" CELLPADDING="0"
><TR
><TD CLASS="infohead"
>Portability</TD
><TD CLASS="infoval"
>GHC</TD
></TR
><TR
><TD CLASS="infohead"
>Stability</TD
><TD CLASS="infoval"
>experimental</TD
></TR
><TR
><TD CLASS="infohead"
>Maintainer</TD
><TD CLASS="infoval"
>bos@serpentine.com, rtomharper@googlemail.com,
duncan@haskell.org</TD
></TR
></TABLE
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="section1"
>Description</TD
></TR
><TR
><TD CLASS="doc"
>Functions used frequently when reading textual data.
</TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="section1"
>Synopsis</TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="body"
><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0"
><TR
><TD CLASS="decl"
><SPAN CLASS="keyword"
>type</SPAN
> <A HREF="#t%3AReader"
>Reader</A
> a = <A HREF="Data-Text-Lazy.html#t%3AText"
>Text</A
> -> <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Data-Either.html#t%3AEither"
>Either</A
> <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Data-Char.html#t%3AString"
>String</A
> (a, <A HREF="Data-Text-Lazy.html#t%3AText"
>Text</A
>)</TD
></TR
><TR
><TD CLASS="s8"
></TD
></TR
><TR
><TD CLASS="decl"
><A HREF="#v%3Adecimal"
>decimal</A
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3AIntegral"
>Integral</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
></TR
><TR
><TD CLASS="s8"
></TD
></TR
><TR
><TD CLASS="decl"
><A HREF="#v%3Ahexadecimal"
>hexadecimal</A
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3AIntegral"
>Integral</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
></TR
><TR
><TD CLASS="s8"
></TD
></TR
><TR
><TD CLASS="decl"
><A HREF="#v%3Asigned"
>signed</A
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ANum"
>Num</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a -> <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
></TR
><TR
><TD CLASS="s8"
></TD
></TR
><TR
><TD CLASS="decl"
><A HREF="#v%3Arational"
>rational</A
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ARealFloat"
>RealFloat</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
></TR
><TR
><TD CLASS="s8"
></TD
></TR
><TR
><TD CLASS="decl"
><A HREF="#v%3Adouble"
>double</A
> :: <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ADouble"
>Double</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="section1"
>Documentation</TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="topdecl"
><TABLE CLASS="declbar"
><TR
><TD CLASS="declname"
><SPAN CLASS="keyword"
>type</SPAN
> <A NAME="t:Reader"
><A NAME="t%3AReader"
></A
></A
><B
>Reader</B
> a = <A HREF="Data-Text-Lazy.html#t%3AText"
>Text</A
> -> <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Data-Either.html#t%3AEither"
>Either</A
> <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Data-Char.html#t%3AString"
>String</A
> (a, <A HREF="Data-Text-Lazy.html#t%3AText"
>Text</A
>)</TD
><TD CLASS="declbut"
><A HREF="src/Data-Text-Lazy-Read.html#Reader"
>Source</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="doc"
>Read some text. If the read succeeds, return its value and the
remaining text, otherwise an error message.
</TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="topdecl"
><TABLE CLASS="declbar"
><TR
><TD CLASS="declname"
><A NAME="v:decimal"
><A NAME="v%3Adecimal"
></A
></A
><B
>decimal</B
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3AIntegral"
>Integral</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
><TD CLASS="declbut"
><A HREF="src/Data-Text-Lazy-Read.html#decimal"
>Source</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="doc"
><P
>Read a decimal integer. The input must begin with at least one
decimal digit, and is consumed until a non-digit or end of string
is reached.
</P
><P
>This function does not handle leading sign characters. If you need
to handle signed input, use <TT
><TT
><A HREF="Data-Text-Lazy-Read.html#v%3Asigned"
>signed</A
></TT
> <TT
><A HREF="Data-Text-Lazy-Read.html#v%3Adecimal"
>decimal</A
></TT
></TT
>.
</P
><P
><EM
>Note</EM
>: For fixed-width integer types, this function does not
attempt to detect overflow, so a sufficiently long input may give
incorrect results.
</P
></TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="topdecl"
><TABLE CLASS="declbar"
><TR
><TD CLASS="declname"
><A NAME="v:hexadecimal"
><A NAME="v%3Ahexadecimal"
></A
></A
><B
>hexadecimal</B
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3AIntegral"
>Integral</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
><TD CLASS="declbut"
><A HREF="src/Data-Text-Lazy-Read.html#hexadecimal"
>Source</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="doc"
><P
>Read a hexadecimal integer, consisting of an optional leading
<TT
>"0x"</TT
> followed by at least one decimal digit. Input is consumed
until a non-hex-digit or end of string is reached. This function
is case insensitive.
</P
><P
>This function does not handle leading sign characters. If you need
to handle signed input, use <TT
><TT
><A HREF="Data-Text-Lazy-Read.html#v%3Asigned"
>signed</A
></TT
> <TT
><A HREF="Data-Text-Lazy-Read.html#v%3Ahexadecimal"
>hexadecimal</A
></TT
></TT
>.
</P
><P
><EM
>Note</EM
>: For fixed-width integer types, this function does not
attempt to detect overflow, so a sufficiently long input may give
incorrect results.
</P
></TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="topdecl"
><TABLE CLASS="declbar"
><TR
><TD CLASS="declname"
><A NAME="v:signed"
><A NAME="v%3Asigned"
></A
></A
><B
>signed</B
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ANum"
>Num</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a -> <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
><TD CLASS="declbut"
><A HREF="src/Data-Text-Lazy-Read.html#signed"
>Source</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="doc"
>Read an optional leading sign character (<TT
>'-'</TT
> or <TT
>'+'</TT
>) and
apply it to the result of applying the given reader.
</TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="topdecl"
><TABLE CLASS="declbar"
><TR
><TD CLASS="declname"
><A NAME="v:rational"
><A NAME="v%3Arational"
></A
></A
><B
>rational</B
> :: <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ARealFloat"
>RealFloat</A
> a => <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> a</TD
><TD CLASS="declbut"
><A HREF="src/Data-Text-Lazy-Read.html#rational"
>Source</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="doc"
><P
>Read a rational number.
</P
><P
>This function accepts an optional leading sign character, followed
by at least one decimal digit. The syntax similar to that accepted
by the <TT
><A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Text-Read.html#v%3Aread"
>read</A
></TT
> function, with the exception that a trailing <TT
>'.'</TT
>
or <TT
>'e'</TT
> <EM
>not</EM
> followed by a number is not consumed.
</P
><P
>Examples:
</P
><PRE
>rational "3" == Right (3.0, "")
rational "3.1" == Right (3.1, "")
rational "3e4" == Right (30000.0, "")
rational "3.1e4" == Right (31000.0, "")
rational ".3" == Left "input does not start with a digit"
rational "e3" == Left "input does not start with a digit"
</PRE
><P
>Examples of differences from <TT
><A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Text-Read.html#v%3Aread"
>read</A
></TT
>:
</P
><PRE
>rational "3.foo" == Right (3.0, ".foo")
rational "3e" == Right (3.0, "e")
</PRE
></TD
></TR
><TR
><TD CLASS="s15"
></TD
></TR
><TR
><TD CLASS="topdecl"
><TABLE CLASS="declbar"
><TR
><TD CLASS="declname"
><A NAME="v:double"
><A NAME="v%3Adouble"
></A
></A
><B
>double</B
> :: <A HREF="Data-Text-Lazy-Read.html#t%3AReader"
>Reader</A
> <A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ADouble"
>Double</A
></TD
><TD CLASS="declbut"
><A HREF="src/Data-Text-Lazy-Read.html#double"
>Source</A
></TD
></TR
></TABLE
></TD
></TR
><TR
><TD CLASS="doc"
><P
>Read a rational number.
</P
><P
>The syntax accepted by this function is the same as for <TT
><A HREF="Data-Text-Lazy-Read.html#v%3Arational"
>rational</A
></TT
>.
</P
><P
><EM
>Note</EM
>: This function is almost ten times faster than <TT
><A HREF="Data-Text-Lazy-Read.html#v%3Arational"
>rational</A
></TT
>,
but is slightly less accurate.
</P
><P
>The <TT
><A HREF="/usr/share/doc/ghc/html/libraries/base-4.2.0.2/Prelude.html#t%3ADouble"
>Double</A
></TT
> type supports about 16 decimal places of accuracy.
For 94.2% of numbers, this function and <TT
><A HREF="Data-Text-Lazy-Read.html#v%3Arational"
>rational</A
></TT
> give identical
results, but for the remaining 5.8%, this function loses precision
around the 15th decimal place. For 0.001% of numbers, this
function will lose precision at the 13th or 14th decimal place.
</P
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