<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head> <!-- Generated by HsColour, http://code.haskell.org/~malcolm/hscolour/ --> <title>Control/Monad/Logic/Class.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <pre><a name="line-1"></a><span class='hs-comment'>-------------------------------------------------------------------------</span> <a name="line-2"></a><span class='hs-comment'>-- |</span> <a name="line-3"></a><span class='hs-comment'>-- Module : Control.Monad.Logic.Class</span> <a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) Dan Doel</span> <a name="line-5"></a><span class='hs-comment'>-- License : BSD3</span> <a name="line-6"></a><span class='hs-comment'>--</span> <a name="line-7"></a><span class='hs-comment'>-- Maintainer : dan.doel@gmail.com</span> <a name="line-8"></a><span class='hs-comment'>-- Stability : experimental</span> <a name="line-9"></a><span class='hs-comment'>-- Portability : non-portable (multi-parameter type classes)</span> <a name="line-10"></a><span class='hs-comment'>--</span> <a name="line-11"></a><span class='hs-comment'>-- A backtracking, logic programming monad.</span> <a name="line-12"></a><span class='hs-comment'>--</span> <a name="line-13"></a><span class='hs-comment'>-- Adapted from the paper</span> <a name="line-14"></a><span class='hs-comment'>-- /Backtracking, Interleaving, and Terminating</span> <a name="line-15"></a><span class='hs-comment'>-- Monad Transformers/, by</span> <a name="line-16"></a><span class='hs-comment'>-- Oleg Kiselyov, Chung-chieh Shan, Daniel P. Friedman, Amr Sabry</span> <a name="line-17"></a><span class='hs-comment'>-- (<<a href="http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf">http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf</a>>)</span> <a name="line-18"></a><span class='hs-comment'>-------------------------------------------------------------------------</span> <a name="line-19"></a> <a name="line-20"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Logic</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadLogic</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>reflect</span><span class='hs-layout'>,</span> <span class='hs-varid'>lnot</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-21"></a> <a name="line-22"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>LazyST</span> <a name="line-23"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>StrictST</span> <a name="line-24"></a> <a name="line-25"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Reader</span> <a name="line-26"></a> <a name="line-27"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Monoid</span> <a name="line-28"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>LazyWT</span> <a name="line-29"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>StrictWT</span> <a name="line-30"></a> <a name="line-31"></a><a name="MonadLogic"></a><span class='hs-comment'>-------------------------------------------------------------------------------</span> <a name="line-32"></a><a name="MonadLogic"></a><span class='hs-comment'>-- | Minimal implementation: msplit</span> <a name="line-33"></a><a name="MonadLogic"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadPlus</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span> <span class='hs-keyword'>where</span> <a name="line-34"></a> <span class='hs-comment'>-- | Attempts to split the computation, giving access to the first</span> <a name="line-35"></a> <span class='hs-comment'>-- result. Satisfies the following laws:</span> <a name="line-36"></a> <span class='hs-comment'>--</span> <a name="line-37"></a> <span class='hs-comment'>-- > msplit mzero == return Nothing</span> <a name="line-38"></a> <span class='hs-comment'>-- > msplit (return a `mplus` m) == return (Just (a, m))</span> <a name="line-39"></a> <span class='hs-varid'>msplit</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-40"></a> <a name="line-41"></a> <span class='hs-comment'>-- | Fair disjunction. It is possible for a logical computation</span> <a name="line-42"></a> <span class='hs-comment'>-- to have an infinite number of potential results, for instance:</span> <a name="line-43"></a> <span class='hs-comment'>--</span> <a name="line-44"></a> <span class='hs-comment'>-- > odds = return 1 `mplus` liftM (2+) odds</span> <a name="line-45"></a> <span class='hs-comment'>--</span> <a name="line-46"></a> <span class='hs-comment'>-- Such computations can cause problems in some circumstances. Consider:</span> <a name="line-47"></a> <span class='hs-comment'>--</span> <a name="line-48"></a> <span class='hs-comment'>-- > do x <- odds `mplus` return 2</span> <a name="line-49"></a> <span class='hs-comment'>-- > if even x then return x else mzero</span> <a name="line-50"></a> <span class='hs-comment'>--</span> <a name="line-51"></a> <span class='hs-comment'>-- Such a computation may never consider the 'return 2', and will</span> <a name="line-52"></a> <span class='hs-comment'>-- therefore never terminate. By contrast, interleave ensures fair</span> <a name="line-53"></a> <span class='hs-comment'>-- consideration of both branches of a disjunction</span> <a name="line-54"></a> <span class='hs-varid'>interleave</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <a name="line-55"></a> <a name="line-56"></a> <span class='hs-comment'>-- | Fair conjunction. Similarly to the previous function, consider</span> <a name="line-57"></a> <span class='hs-comment'>-- the distributivity law for MonadPlus:</span> <a name="line-58"></a> <span class='hs-comment'>--</span> <a name="line-59"></a> <span class='hs-comment'>-- > (mplus a b) >>= k = (a >>= k) `mplus` (b >>= k)</span> <a name="line-60"></a> <span class='hs-comment'>--</span> <a name="line-61"></a> <span class='hs-comment'>-- If 'a >>= k' can backtrack arbitrarily many tmes, (b >>= k) may never</span> <a name="line-62"></a> <span class='hs-comment'>-- be considered. (>>-) takes similar care to consider both branches of</span> <a name="line-63"></a> <span class='hs-comment'>-- a disjunctive computation.</span> <a name="line-64"></a> <span class='hs-layout'>(</span><span class='hs-varop'>>>-</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span> <a name="line-65"></a> <span class='hs-keyword'>infixl</span> <span class='hs-num'>1</span> <span class='hs-varop'>>>-</span> <a name="line-66"></a> <a name="line-67"></a> <span class='hs-comment'>-- | Logical conditional. The equivalent of Prolog's soft-cut. If its</span> <a name="line-68"></a> <span class='hs-comment'>-- first argument succeeds at all, then the results will be fed into</span> <a name="line-69"></a> <span class='hs-comment'>-- the success branch. Otherwise, the failure branch is taken.</span> <a name="line-70"></a> <span class='hs-comment'>-- satisfies the following laws:</span> <a name="line-71"></a> <span class='hs-comment'>--</span> <a name="line-72"></a> <span class='hs-comment'>-- > ifte (return a) th el == th a</span> <a name="line-73"></a> <span class='hs-comment'>-- > ifte mzero th el == el</span> <a name="line-74"></a> <span class='hs-comment'>-- > ifte (return a `mplus` m) th el == th a `mplus` (m >>= th)</span> <a name="line-75"></a> <span class='hs-varid'>ifte</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span> <a name="line-76"></a> <a name="line-77"></a> <span class='hs-comment'>-- | Pruning. Selects one result out of many. Useful for when multiple</span> <a name="line-78"></a> <span class='hs-comment'>-- results of a computation will be equivalent, or should be treated as</span> <a name="line-79"></a> <span class='hs-comment'>-- such.</span> <a name="line-80"></a> <span class='hs-varid'>once</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <a name="line-81"></a> <a name="line-82"></a> <span class='hs-comment'>-- All the class functions besides msplit can be derived from msplit, if</span> <a name="line-83"></a> <span class='hs-comment'>-- desired</span> <a name="line-84"></a> <span class='hs-varid'>interleave</span> <span class='hs-varid'>m1</span> <span class='hs-varid'>m2</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>msplit</span> <span class='hs-varid'>m1</span> <span class='hs-varop'>>>=</span> <a name="line-85"></a> <span class='hs-varid'>maybe</span> <span class='hs-varid'>m2</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'>m1'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varid'>a</span> <span class='hs-varop'>`mplus`</span> <span class='hs-varid'>interleave</span> <span class='hs-varid'>m2</span> <span class='hs-varid'>m1'</span><span class='hs-layout'>)</span> <a name="line-86"></a> <a name="line-87"></a> <span class='hs-varid'>m</span> <span class='hs-varop'>>>-</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>m'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-varid'>m</span> <a name="line-88"></a> <span class='hs-varid'>interleave</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>m'</span> <span class='hs-varop'>>>-</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <a name="line-89"></a> <a name="line-90"></a> <span class='hs-varid'>ifte</span> <span class='hs-varid'>t</span> <span class='hs-varid'>th</span> <span class='hs-varid'>el</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>msplit</span> <span class='hs-varid'>t</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>maybe</span> <span class='hs-varid'>el</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'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>th</span> <span class='hs-varid'>a</span> <span class='hs-varop'>`mplus`</span> <span class='hs-layout'>(</span><span class='hs-varid'>m</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>th</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-91"></a> <a name="line-92"></a> <span class='hs-varid'>once</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-varid'>m</span> <a name="line-93"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>a</span> <a name="line-94"></a> <a name="line-95"></a> <a name="line-96"></a><a name="reflect"></a><span class='hs-comment'>-------------------------------------------------------------------------------</span> <a name="line-97"></a><span class='hs-comment'>-- | The inverse of msplit. Satisfies the following law:</span> <a name="line-98"></a><span class='hs-comment'>--</span> <a name="line-99"></a><span class='hs-comment'>-- > msplit m >>= reflect == m</span> <a name="line-100"></a><span class='hs-definition'>reflect</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <a name="line-101"></a><span class='hs-definition'>reflect</span> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mzero</span> <a name="line-102"></a><span class='hs-definition'>reflect</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-varid'>a</span> <span class='hs-varop'>`mplus`</span> <span class='hs-varid'>m</span> <a name="line-103"></a> <a name="line-104"></a><a name="lnot"></a><span class='hs-comment'>-- | Inverts a logic computation. If @m@ succeeds with at least one value,</span> <a name="line-105"></a><span class='hs-comment'>-- @lnot m@ fails. If @m@ fails, then @lnot m@ succeeds the value @()@.</span> <a name="line-106"></a><span class='hs-definition'>lnot</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-conid'>()</span> <a name="line-107"></a><span class='hs-definition'>lnot</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ifte</span> <span class='hs-layout'>(</span><span class='hs-varid'>once</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-varid'>mzero</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>return</span> <span class='hs-conid'>()</span><span class='hs-layout'>)</span> <a name="line-108"></a> <a name="line-109"></a><a name="instance%20MonadLogic%20%5b%5d"></a><span class='hs-comment'>-- An instance of MonadLogic for lists</span> <a name="line-110"></a><a name="instance%20MonadLogic%20%5b%5d"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadLogic</span> <span class='hs-conid'>[]</span> <span class='hs-keyword'>where</span> <a name="line-111"></a> <span class='hs-varid'>msplit</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span> <a name="line-112"></a> <span class='hs-varid'>msplit</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-conop'>:</span><span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span> <span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <a name="line-113"></a> <a name="line-114"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- Some of these may be questionable instances. Splitting a transformer does</span> <a name="line-115"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- not allow you to provide different input to the monadic object returned.</span> <a name="line-116"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- So, for instance, in:</span> <a name="line-117"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>--</span> <a name="line-118"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- let Just (_, rm') = runReaderT (msplit rm) r</span> <a name="line-119"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- in runReaderT rm' r'</span> <a name="line-120"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>--</span> <a name="line-121"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- The "r'" parameter will be ignored, as "r" was already threaded through the</span> <a name="line-122"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- computation. The results are similar for StateT. However, this is likely not</span> <a name="line-123"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- an issue as most uses of msplit (all the ones in this library, at least) would</span> <a name="line-124"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-comment'>-- not allow for that anyway.</span> <a name="line-125"></a><a name="instance%20MonadLogic%20(ReaderT%20e%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadLogic</span> <span class='hs-layout'>(</span><span class='hs-conid'>ReaderT</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-126"></a> <span class='hs-varid'>msplit</span> <span class='hs-varid'>rm</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ReaderT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>e</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-varop'>$</span> <span class='hs-varid'>runReaderT</span> <span class='hs-varid'>rm</span> <span class='hs-varid'>e</span> <a name="line-127"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>r</span> <span class='hs-keyword'>of</span> <a name="line-128"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-conid'>Nothing</span> <a name="line-129"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-130"></a> <a name="line-131"></a><a name="instance%20MonadLogic%20(StrictST.StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadLogic</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-132"></a> <span class='hs-varid'>msplit</span> <span class='hs-varid'>sm</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <a name="line-133"></a> <span class='hs-keyword'>do</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>sm</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-134"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>r</span> <span class='hs-keyword'>of</span> <a name="line-135"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Nothing</span><span class='hs-layout'>,</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-136"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-137"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <a name="line-138"></a> <a name="line-139"></a> <span class='hs-varid'>interleave</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>mb</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <a name="line-140"></a> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>s</span> <span class='hs-varop'>`interleave`</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>mb</span> <span class='hs-varid'>s</span> <a name="line-141"></a> <a name="line-142"></a> <span class='hs-varid'>ma</span> <span class='hs-varop'>>>-</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <a name="line-143"></a> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>s</span> <span class='hs-varop'>>>-</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'>s'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>s'</span> <a name="line-144"></a> <a name="line-145"></a> <span class='hs-varid'>ifte</span> <span class='hs-varid'>t</span> <span class='hs-varid'>th</span> <span class='hs-varid'>el</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>ifte</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>t</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-146"></a> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-layout'>(</span><span class='hs-varid'>th</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <a name="line-147"></a> <span class='hs-layout'>(</span><span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>el</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-148"></a> <a name="line-149"></a> <span class='hs-varid'>once</span> <span class='hs-varid'>ma</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>once</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-150"></a> <a name="line-151"></a><a name="instance%20MonadLogic%20(LazyST.StateT%20s%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadLogic</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-152"></a> <span class='hs-varid'>msplit</span> <span class='hs-varid'>sm</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <a name="line-153"></a> <span class='hs-keyword'>do</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>sm</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-154"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>r</span> <span class='hs-keyword'>of</span> <a name="line-155"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Nothing</span><span class='hs-layout'>,</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-156"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-157"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <a name="line-158"></a> <a name="line-159"></a> <span class='hs-varid'>interleave</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>mb</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <a name="line-160"></a> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>s</span> <span class='hs-varop'>`interleave`</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>mb</span> <span class='hs-varid'>s</span> <a name="line-161"></a> <a name="line-162"></a> <span class='hs-varid'>ma</span> <span class='hs-varop'>>>-</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <a name="line-163"></a> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>s</span> <span class='hs-varop'>>>-</span> <span class='hs-keyglyph'>\</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>s'</span> <a name="line-164"></a> <a name="line-165"></a> <span class='hs-varid'>ifte</span> <span class='hs-varid'>t</span> <span class='hs-varid'>th</span> <span class='hs-varid'>el</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>ifte</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>t</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-166"></a> <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'>s'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-layout'>(</span><span class='hs-varid'>th</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>s'</span><span class='hs-layout'>)</span> <a name="line-167"></a> <span class='hs-layout'>(</span><span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>el</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-168"></a> <a name="line-169"></a> <span class='hs-varid'>once</span> <span class='hs-varid'>ma</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>s</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>once</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyST</span><span class='hs-varop'>.</span><span class='hs-varid'>runStateT</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-170"></a> <a name="line-171"></a><a name="instance%20MonadLogic%20(StrictWT.WriterT%20w%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadLogic</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-172"></a> <span class='hs-varid'>msplit</span> <span class='hs-varid'>wm</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-173"></a> <span class='hs-keyword'>do</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>wm</span><span class='hs-layout'>)</span> <a name="line-174"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>r</span> <span class='hs-keyword'>of</span> <a name="line-175"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Nothing</span><span class='hs-layout'>,</span> <span class='hs-varid'>mempty</span><span class='hs-layout'>)</span> <a name="line-176"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>w</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-177"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span> <a name="line-178"></a> <a name="line-179"></a> <span class='hs-varid'>interleave</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>mb</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-180"></a> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>ma</span> <span class='hs-varop'>`interleave`</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>mb</span> <a name="line-181"></a> <a name="line-182"></a> <span class='hs-varid'>ma</span> <span class='hs-varop'>>>-</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-183"></a> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>ma</span> <span class='hs-varop'>>>-</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'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-184"></a> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>tell</span> <span class='hs-varid'>w</span> <span class='hs-varop'>>></span> <span class='hs-varid'>f</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <a name="line-185"></a> <a name="line-186"></a> <span class='hs-varid'>ifte</span> <span class='hs-varid'>t</span> <span class='hs-varid'>th</span> <span class='hs-varid'>el</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-187"></a> <span class='hs-varid'>ifte</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <a name="line-188"></a> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>tell</span> <span class='hs-varid'>w</span> <span class='hs-varop'>>></span> <span class='hs-varid'>th</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-189"></a> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>el</span><span class='hs-layout'>)</span> <a name="line-190"></a> <a name="line-191"></a> <span class='hs-varid'>once</span> <span class='hs-varid'>ma</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <span class='hs-varid'>once</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>ma</span><span class='hs-layout'>)</span> <a name="line-192"></a> <a name="line-193"></a><a name="instance%20MonadLogic%20(LazyWT.WriterT%20w%20m)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadLogic</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadLogic</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-194"></a> <span class='hs-varid'>msplit</span> <span class='hs-varid'>wm</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-195"></a> <span class='hs-keyword'>do</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>msplit</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>wm</span><span class='hs-layout'>)</span> <a name="line-196"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>r</span> <span class='hs-keyword'>of</span> <a name="line-197"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Nothing</span><span class='hs-layout'>,</span> <span class='hs-varid'>mempty</span><span class='hs-layout'>)</span> <a name="line-198"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>w</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-199"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span> <a name="line-200"></a> <a name="line-201"></a> <span class='hs-varid'>interleave</span> <span class='hs-varid'>ma</span> <span class='hs-varid'>mb</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-202"></a> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>ma</span> <span class='hs-varop'>`interleave`</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>mb</span> <a name="line-203"></a> <a name="line-204"></a> <span class='hs-varid'>ma</span> <span class='hs-varop'>>>-</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-205"></a> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>ma</span> <span class='hs-varop'>>>-</span> <span class='hs-keyglyph'>\</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span><span class='hs-varid'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-206"></a> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>tell</span> <span class='hs-varid'>w</span> <span class='hs-varop'>>></span> <span class='hs-varid'>f</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <a name="line-207"></a> <a name="line-208"></a> <span class='hs-varid'>ifte</span> <span class='hs-varid'>t</span> <span class='hs-varid'>th</span> <span class='hs-varid'>el</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <a name="line-209"></a> <span class='hs-varid'>ifte</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>t</span><span class='hs-layout'>)</span> <a name="line-210"></a> <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'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>tell</span> <span class='hs-varid'>w</span> <span class='hs-varop'>>></span> <span class='hs-varid'>th</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-211"></a> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>el</span><span class='hs-layout'>)</span> <a name="line-212"></a> <a name="line-213"></a> <span class='hs-varid'>once</span> <span class='hs-varid'>ma</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varop'>$</span> <span class='hs-varid'>once</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyWT</span><span class='hs-varop'>.</span><span class='hs-varid'>runWriterT</span> <span class='hs-varid'>ma</span><span class='hs-layout'>)</span> </pre></body> 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