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<title>src/Text/ParserCombinators/Poly/Lex.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>-- Author: Malcolm Wallace</span>
<a name="line-2"></a>
<a name="line-3"></a><span class='hs-comment'>-- | In a strict language, where creating the entire input list of tokens</span>
<a name="line-4"></a><span class='hs-comment'>-- in one shot may be infeasible, we can use a lazy "callback" kind of</span>
<a name="line-5"></a><span class='hs-comment'>-- architecture instead. The lexer returns a single token at a time,</span>
<a name="line-6"></a><span class='hs-comment'>-- together with a continuation.</span>
<a name="line-7"></a><span class='hs-comment'>--</span>
<a name="line-8"></a><span class='hs-comment'>-- This module defines a Parser type (capable of use with the Poly</span>
<a name="line-9"></a><span class='hs-comment'>-- combinators), specialised to the callback-lexer style of input stream.</span>
<a name="line-10"></a>
<a name="line-11"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Text</span><span class='hs-varop'>.</span><span class='hs-conid'>ParserCombinators</span><span class='hs-varop'>.</span><span class='hs-conid'>Poly</span><span class='hs-varop'>.</span><span class='hs-conid'>Lex</span>
<a name="line-12"></a> <span class='hs-layout'>(</span> <span class='hs-comment'>-- * The Parser datatype</span>
<a name="line-13"></a> <span class='hs-conid'>LexReturn</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-14"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>Parser</span><span class='hs-layout'>(</span><span class='hs-conid'>P</span><span class='hs-layout'>)</span>
<a name="line-15"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>Result</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-16"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>runParser</span>
<a name="line-17"></a> <span class='hs-comment'>-- ** Basic parsers</span>
<a name="line-18"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>next</span>
<a name="line-19"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>eof</span>
<a name="line-20"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>satisfy</span>
<a name="line-21"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>onFail</span>
<a name="line-22"></a> <span class='hs-comment'>-- ** Re-parsing</span>
<a name="line-23"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>reparse</span>
<a name="line-24"></a> <span class='hs-comment'>-- * Re-export all more general combinators</span>
<a name="line-25"></a> <span class='hs-layout'>,</span> <span class='hs-keyword'>module</span> <span class='hs-conid'>Text</span><span class='hs-varop'>.</span><span class='hs-conid'>ParserCombinators</span><span class='hs-varop'>.</span><span class='hs-conid'>Poly</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span>
<a name="line-26"></a> <span class='hs-layout'>,</span> <span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Applicative</span>
<a name="line-27"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-28"></a>
<a name="line-29"></a>
<a name="line-30"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Text</span><span class='hs-varop'>.</span><span class='hs-conid'>ParserCombinators</span><span class='hs-varop'>.</span><span class='hs-conid'>Poly</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span>
<a name="line-31"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Text</span><span class='hs-varop'>.</span><span class='hs-conid'>ParserCombinators</span><span class='hs-varop'>.</span><span class='hs-conid'>Poly</span><span class='hs-varop'>.</span><span class='hs-conid'>Result</span>
<a name="line-32"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Applicative</span>
<a name="line-33"></a>
<a name="line-34"></a><a name="LexReturn"></a><span class='hs-comment'>-- | In a strict language, where creating the entire input list of tokens</span>
<a name="line-35"></a><a name="LexReturn"></a><span class='hs-comment'>-- in one shot may be infeasible, we can use a lazy "callback" kind of</span>
<a name="line-36"></a><a name="LexReturn"></a><span class='hs-comment'>-- architecture instead. The lexer returns a single token at a time,</span>
<a name="line-37"></a><a name="LexReturn"></a><span class='hs-comment'>-- together with a continuation. The @next@ parser is responsible for </span>
<a name="line-38"></a><a name="LexReturn"></a><span class='hs-comment'>-- pulling on the token stream, applying the continuation where necessary.</span>
<a name="line-39"></a><a name="LexReturn"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span> <span class='hs-conid'>String</span> <span class='hs-layout'>(</span><span class='hs-conid'>String</span><span class='hs-keyglyph'>-></span><span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span>
<a name="line-40"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>LexFinish</span>
<a name="line-41"></a>
<a name="line-42"></a><a name="Parser"></a><span class='hs-comment'>-- | This @Parser@ datatype is a specialised parsing monad with error</span>
<a name="line-43"></a><a name="Parser"></a><span class='hs-comment'>-- reporting. This version is specialised to pre-lexed String input,</span>
<a name="line-44"></a><a name="Parser"></a><span class='hs-comment'>-- where the lexer has been written to yield a @LexReturn@.</span>
<a name="line-45"></a><a name="Parser"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Result</span> <span class='hs-layout'>(</span><span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-46"></a>
<a name="line-47"></a><a name="runParser"></a><span class='hs-comment'>-- | Apply a parser to an input token sequence.</span>
<a name="line-48"></a><span class='hs-definition'>runParser</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-conid'>String</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>String</span><span class='hs-layout'>)</span>
<a name="line-49"></a><span class='hs-definition'>runParser</span> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>b</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>-></span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>stripLex</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>resultToEither</span> <span class='hs-varop'>.</span> <span class='hs-varid'>p</span>
<a name="line-50"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>stripLex</span> <span class='hs-conid'>LexFinish</span> <span class='hs-keyglyph'>=</span> <span class='hs-str'>""</span>
<a name="line-51"></a> <span class='hs-varid'>stripLex</span> <span class='hs-layout'>(</span><span class='hs-conid'>LexReturn</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>s</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>s</span>
<a name="line-52"></a>
<a name="line-53"></a><a name="instance%20Functor%20(Parser%20t)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Functor</span> <span class='hs-layout'>(</span><span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-54"></a> <span class='hs-varid'>fmap</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-varid'>fmap</span> <span class='hs-varid'>f</span> <span class='hs-varop'>.</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span>
<a name="line-55"></a>
<a name="line-56"></a><a name="instance%20Monad%20(Parser%20t)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-57"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>ts</span><span class='hs-keyglyph'>-></span> <span class='hs-conid'>Success</span> <span class='hs-varid'>ts</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span>
<a name="line-58"></a> <span class='hs-varid'>fail</span> <span class='hs-varid'>e</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>ts</span><span class='hs-keyglyph'>-></span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>ts</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span>
<a name="line-59"></a> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-varid'>continue</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span>
<a name="line-60"></a> <span class='hs-keyword'>where</span>
<a name="line-61"></a> <span class='hs-varid'>continue</span> <span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-varid'>ts</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>let</span> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>g'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>g</span> <span class='hs-varid'>x</span> <span class='hs-keyword'>in</span> <span class='hs-varid'>g'</span> <span class='hs-varid'>ts</span>
<a name="line-62"></a> <span class='hs-varid'>continue</span> <span class='hs-layout'>(</span><span class='hs-conid'>Committed</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Committed</span> <span class='hs-layout'>(</span><span class='hs-varid'>continue</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-63"></a> <span class='hs-varid'>continue</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-varid'>ts</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>ts</span> <span class='hs-varid'>e</span>
<a name="line-64"></a>
<a name="line-65"></a><a name="instance%20Commitment%20(Parser%20t)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Commitment</span> <span class='hs-layout'>(</span><span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-66"></a> <span class='hs-varid'>commit</span> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-conid'>Committed</span> <span class='hs-varop'>.</span> <span class='hs-varid'>squash</span> <span class='hs-varop'>.</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span>
<a name="line-67"></a> <span class='hs-keyword'>where</span>
<a name="line-68"></a> <span class='hs-varid'>squash</span> <span class='hs-layout'>(</span><span class='hs-conid'>Committed</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>squash</span> <span class='hs-varid'>r</span>
<a name="line-69"></a> <span class='hs-varid'>squash</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>r</span>
<a name="line-70"></a> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span> <span class='hs-varop'>`adjustErr`</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-varid'>adjust</span> <span class='hs-varop'>.</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span>
<a name="line-71"></a> <span class='hs-keyword'>where</span>
<a name="line-72"></a> <span class='hs-varid'>adjust</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-varid'>z</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>z</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span>
<a name="line-73"></a> <span class='hs-varid'>adjust</span> <span class='hs-layout'>(</span><span class='hs-conid'>Committed</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Committed</span> <span class='hs-layout'>(</span><span class='hs-varid'>adjust</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-74"></a> <span class='hs-varid'>adjust</span> <span class='hs-varid'>good</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>good</span>
<a name="line-75"></a>
<a name="line-76"></a> <span class='hs-varid'>oneOf'</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>accum</span> <span class='hs-conid'>[]</span>
<a name="line-77"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>accum</span> <span class='hs-varid'>errs</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span>
<a name="line-78"></a> <span class='hs-varid'>fail</span> <span class='hs-layout'>(</span><span class='hs-str'>"failed to parse any of the possible choices:\n"</span>
<a name="line-79"></a> <span class='hs-varop'>++</span><span class='hs-layout'>(</span><span class='hs-varid'>indent</span> <span class='hs-num'>2</span> <span class='hs-varop'>.</span> <span class='hs-varid'>unlines</span> <span class='hs-varop'>.</span> <span class='hs-varid'>map</span> <span class='hs-varid'>showErr</span> <span class='hs-varop'>.</span> <span class='hs-varid'>reverse</span> <span class='hs-varop'>$</span> <span class='hs-varid'>errs</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-80"></a> <span class='hs-varid'>accum</span> <span class='hs-varid'>errs</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-conid'>P</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span><span class='hs-conop'>:</span><span class='hs-varid'>ps</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-81"></a> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>ts</span><span class='hs-keyglyph'>-></span> <span class='hs-keyword'>case</span> <span class='hs-varid'>p</span> <span class='hs-varid'>ts</span> <span class='hs-keyword'>of</span>
<a name="line-82"></a> <span class='hs-conid'>Failure</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>err</span> <span class='hs-keyglyph'>-></span>
<a name="line-83"></a> <span class='hs-keyword'>let</span> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>p'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>accum</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-varid'>err</span><span class='hs-layout'>)</span><span class='hs-conop'>:</span><span class='hs-varid'>errs</span><span class='hs-layout'>)</span> <span class='hs-varid'>ps</span>
<a name="line-84"></a> <span class='hs-keyword'>in</span> <span class='hs-varid'>p'</span> <span class='hs-varid'>ts</span>
<a name="line-85"></a> <span class='hs-varid'>r</span><span class='hs-keyglyph'>@</span><span class='hs-layout'>(</span><span class='hs-conid'>Success</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span>
<a name="line-86"></a> <span class='hs-varid'>r</span><span class='hs-keyglyph'>@</span><span class='hs-layout'>(</span><span class='hs-conid'>Committed</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span> <span class='hs-layout'>)</span>
<a name="line-87"></a> <span class='hs-varid'>showErr</span> <span class='hs-layout'>(</span><span class='hs-varid'>name</span><span class='hs-layout'>,</span><span class='hs-varid'>err</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>name</span> <span class='hs-varop'>++</span> <span class='hs-str'>"\n"</span> <span class='hs-varop'>++</span> <span class='hs-varid'>indent</span> <span class='hs-num'>2</span> <span class='hs-varid'>err</span>
<a name="line-88"></a>
<a name="line-89"></a><span class='hs-keyword'>infixl</span> <span class='hs-num'>6</span> <span class='hs-varop'>`onFail`</span> <span class='hs-comment'>-- not sure about precedence 6?</span>
<a name="line-90"></a>
<a name="line-91"></a><a name="onFail"></a><span class='hs-comment'>-- | @p `onFail` q@ means parse p, unless p fails, in which case</span>
<a name="line-92"></a><a name="onFail"></a><span class='hs-comment'>-- parse q instead.</span>
<a name="line-93"></a><a name="onFail"></a><span class='hs-comment'>-- Can be chained together to give multiple attempts to parse something.</span>
<a name="line-94"></a><a name="onFail"></a><span class='hs-comment'>-- (Note that q could itself be a failing parser, e.g. to change the error</span>
<a name="line-95"></a><a name="onFail"></a><span class='hs-comment'>-- message from that defined in p to something different.)</span>
<a name="line-96"></a><a name="onFail"></a><span class='hs-comment'>-- However, a severe failure in p cannot be ignored.</span>
<a name="line-97"></a><a name="onFail"></a><span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>p</span><span class='hs-layout'>)</span> <span class='hs-varop'>`onFail`</span> <span class='hs-layout'>(</span><span class='hs-conid'>P</span> <span class='hs-varid'>q</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>ts</span><span class='hs-keyglyph'>-></span> <span class='hs-varid'>continue</span> <span class='hs-varid'>ts</span> <span class='hs-varop'>$</span> <span class='hs-varid'>p</span> <span class='hs-varid'>ts</span><span class='hs-layout'>)</span>
<a name="line-98"></a> <span class='hs-keyword'>where</span>
<a name="line-99"></a> <span class='hs-varid'>continue</span> <span class='hs-varid'>ts</span> <span class='hs-layout'>(</span><span class='hs-conid'>Failure</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>q</span> <span class='hs-varid'>ts</span>
<a name="line-100"></a> <span class='hs-comment'>-- continue _ (Committed r) = r -- no, remain Committed</span>
<a name="line-101"></a> <span class='hs-varid'>continue</span> <span class='hs-keyword'>_</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>r</span>
<a name="line-102"></a>
<a name="line-103"></a><a name="instance%20Applicative%20(Parser%20t)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Applicative</span> <span class='hs-layout'>(</span><span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-104"></a> <span class='hs-varid'>pure</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-varid'>f</span>
<a name="line-105"></a> <span class='hs-varid'>pf</span> <span class='hs-varop'><*></span> <span class='hs-varid'>px</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <span class='hs-layout'>{</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>pf</span><span class='hs-layout'>;</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>px</span><span class='hs-layout'>;</span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-layout'>}</span>
<a name="line-106"></a><span class='hs-cpp'>#if defined(GLASGOW_HASKELL) && GLASGOW_HASKELL > 610</span>
<a name="line-107"></a> <span class='hs-varid'>p</span> <span class='hs-varop'><*</span> <span class='hs-varid'>q</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>p</span> <span class='hs-varop'>`discard`</span> <span class='hs-varid'>q</span>
<a name="line-108"></a><span class='hs-cpp'>#endif</span>
<a name="line-109"></a>
<a name="line-110"></a><a name="instance%20Alternative%20(Parser%20t)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Alternative</span> <span class='hs-layout'>(</span><span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-111"></a> <span class='hs-varid'>empty</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fail</span> <span class='hs-str'>"no parse"</span>
<a name="line-112"></a> <span class='hs-varid'>p</span> <span class='hs-varop'><|></span> <span class='hs-varid'>q</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>p</span> <span class='hs-varop'>`onFail`</span> <span class='hs-varid'>q</span>
<a name="line-113"></a>
<a name="line-114"></a><a name="instance%20PolyParse%20(Parser%20t)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>PolyParse</span> <span class='hs-layout'>(</span><span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span>
<a name="line-115"></a>
<a name="line-116"></a><span class='hs-comment'>------------------------------------------------------------------------</span>
<a name="line-117"></a>
<a name="line-118"></a><a name="next"></a><span class='hs-comment'>-- | Simply return the next token in the input tokenstream.</span>
<a name="line-119"></a><span class='hs-definition'>next</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span> <span class='hs-varid'>t</span>
<a name="line-120"></a><span class='hs-definition'>next</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>ts</span><span class='hs-keyglyph'>-></span> <span class='hs-keyword'>case</span> <span class='hs-varid'>ts</span> <span class='hs-keyword'>of</span>
<a name="line-121"></a> <span class='hs-conid'>LexFinish</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>ts</span> <span class='hs-str'>"Ran out of input (EOF)"</span>
<a name="line-122"></a> <span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span> <span class='hs-varid'>s</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Success</span> <span class='hs-layout'>(</span><span class='hs-varid'>k</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span>
<a name="line-123"></a>
<a name="line-124"></a><a name="eof"></a><span class='hs-comment'>-- | Succeed if the end of file/input has been reached, fail otherwise.</span>
<a name="line-125"></a><span class='hs-definition'>eof</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span> <span class='hs-conid'>()</span>
<a name="line-126"></a><span class='hs-definition'>eof</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>ts</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>case</span> <span class='hs-varid'>ts</span> <span class='hs-keyword'>of</span>
<a name="line-127"></a> <span class='hs-conid'>LexFinish</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Success</span> <span class='hs-varid'>ts</span> <span class='hs-conid'>()</span>
<a name="line-128"></a> <span class='hs-conid'>LexReturn</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Failure</span> <span class='hs-varid'>ts</span> <span class='hs-str'>"Expected end of input (EOF)"</span> <span class='hs-layout'>)</span>
<a name="line-129"></a>
<a name="line-130"></a><a name="satisfy"></a><span class='hs-comment'>-- | Return the next token if it satisfies the given predicate.</span>
<a name="line-131"></a><span class='hs-definition'>satisfy</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-varid'>t</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Bool</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span> <span class='hs-varid'>t</span>
<a name="line-132"></a><span class='hs-definition'>satisfy</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <span class='hs-layout'>{</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>next</span>
<a name="line-133"></a> <span class='hs-layout'>;</span> <span class='hs-keyword'>if</span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span> <span class='hs-keyword'>then</span> <span class='hs-varid'>return</span> <span class='hs-varid'>x</span> <span class='hs-keyword'>else</span> <span class='hs-varid'>fail</span> <span class='hs-str'>"Parse.satisfy: failed"</span>
<a name="line-134"></a> <span class='hs-layout'>}</span>
<a name="line-135"></a>
<a name="line-136"></a><a name="reparse"></a><span class='hs-comment'>------------------------------------------------------------------------</span>
<a name="line-137"></a><span class='hs-comment'>-- | Push some tokens back onto the front of the input stream and reparse.</span>
<a name="line-138"></a><span class='hs-comment'>-- This is useful e.g. for recursively expanding macros. When the</span>
<a name="line-139"></a><span class='hs-comment'>-- user-parser recognises a macro use, it can lookup the macro</span>
<a name="line-140"></a><span class='hs-comment'>-- expansion from the parse state, lex it, and then stuff the</span>
<a name="line-141"></a><span class='hs-comment'>-- lexed expansion back down into the parser.</span>
<a name="line-142"></a><span class='hs-definition'>reparse</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>t</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Parser</span> <span class='hs-varid'>t</span> <span class='hs-conid'>()</span>
<a name="line-143"></a><span class='hs-definition'>reparse</span> <span class='hs-varid'>ts</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>P</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>inp</span><span class='hs-keyglyph'>-></span> <span class='hs-conid'>Success</span> <span class='hs-layout'>(</span><span class='hs-varid'>ts</span> <span class='hs-varop'>`prefix`</span> <span class='hs-varid'>inp</span><span class='hs-layout'>)</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span>
<a name="line-144"></a> <span class='hs-keyword'>where</span>
<a name="line-145"></a> <span class='hs-layout'>(</span><span class='hs-varid'>t</span><span class='hs-conop'>:</span><span class='hs-varid'>ts</span><span class='hs-layout'>)</span> <span class='hs-varop'>`prefix`</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LexReturn</span> <span class='hs-varid'>t</span> <span class='hs-str'>""</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-layout'>(</span><span class='hs-varid'>ts</span> <span class='hs-varop'>`prefix`</span> <span class='hs-varid'>k</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-146"></a> <span class='hs-conid'>[]</span> <span class='hs-varop'>`prefix`</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>k</span>
<a name="line-147"></a>
<a name="line-148"></a><span class='hs-comment'>------------------------------------------------------------------------</span>
</pre></body>
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