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<span class="hidden">CLiki - memoize-form</span>
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<div id="content"><div id="content-area"><div id="article-title">memoize-form</div><div id="article">A simpler need than memoizing the results of a function with arguments is that of memoizing the results of a form. The tricky thing here is to do it just inline in the code, without using a global variable or such.<p><div class="code"><span class="nonparen"><span class="comment">;; (MEMOIZED form) memoizes the result of form from its first evaluation.
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</span><span class="comment">;; Use like this:
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</span><span class="comment">;; (defun secret-password (...) ....... (memoized (random 1000)) ......)
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</span>
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<span class="paren1">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/speope_eval-when.html" class="symbol"><i><span class="symbol">eval-when</span></i></a> <span class="paren2">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/fun_compile.html" class="symbol">compile</a> <a href="https://www.cliki.net/site/HyperSpec/Body/fun_load.html" class="symbol">load</a> <a href="https://www.cliki.net/site/HyperSpec/Body/fun_eval.html" class="symbol">eval</a></span>)</span>
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<span class="paren2">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/mac_whencm_unless.html" class="symbol">when</a> <span class="paren3">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/fun_eval.html" class="symbol">eval</a> '<span class="paren4">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/speope_fletcm_scm_macrolet.html" class="symbol"><i><span class="symbol">flet</span></i></a> <span class="paren5">(<span class="nonparen"><span class="paren6">(<span class="nonparen">ltv <span class="paren1">(<span class="nonparen"></span>)</span> <span class="paren1">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/speope_load-time-value.html" class="symbol"><i><span class="symbol">load-time-value</span></i></a> <span class="paren2">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/any_cons.html" class="symbol">cons</a> <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">nil</a> <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">nil</a></span>)</span></span>)</span></span>)</span></span>)</span> <span class="paren5">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/fun_eq.html" class="symbol">eq</a> <span class="paren6">(<span class="nonparen">ltv</span>)</span> <span class="paren6">(<span class="nonparen">ltv</span>)</span></span>)</span></span>)</span></span>)</span>
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<span class="paren3">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/mac_pushnew.html" class="symbol">pushnew</a> <span class="keyword">:eval-uses-compiler</span> <a href="https://www.cliki.net/site/HyperSpec/Body/var_stfeaturesst.html" class="symbol"><span class="special">*features*</span></a></span>)</span></span>)</span></span>)</span>
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<span class="paren1">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/mac_defmacro.html" class="symbol"><i><span class="symbol">defmacro</span></i></a> memoized <span class="paren2">(<span class="nonparen">form</span>)</span>
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`<span class="paren2">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/speope_letcm_letst.html" class="symbol"><i><span class="symbol">LET</span></i></a> <span class="paren3">(<span class="nonparen"><span class="paren4">(<span class="nonparen">MEMORY
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<span class="paren5">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/speope_if.html" class="symbol"><i><span class="symbol">IF</span></i></a> #-eval-uses-compiler <span class="paren6">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/speope_eval-when.html" class="symbol"><i><span class="symbol">EVAL-WHEN</span></i></a> <span class="paren1">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/fun_eval.html" class="symbol">EVAL</a></span>)</span> <a href="https://www.cliki.net/site/HyperSpec/Body/any_t.html" class="symbol">T</a></span>)</span> #+eval-uses-compiler <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">NIL</a>
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',<span class="paren6">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/any_cons.html" class="symbol">cons</a> <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">nil</a> <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">nil</a></span>)</span>
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<span class="comment">;; Careful: Different expansions of MEMOIZED forms must yield
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</span> <span class="comment">;; LOAD-TIME-VALUE forms that are not EQ, otherwise compile-file
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</span> <span class="comment">;; will coalesce these LOAD-TIME-VALUE forms. Therefore here we
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</span> <span class="comment">;; explicitly cons up the list and don't use backquote.
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</span> ,<span class="paren6">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/any_list.html" class="symbol">list</a> '<a href="https://www.cliki.net/site/HyperSpec/Body/speope_load-time-value.html" class="symbol"><i><span class="symbol">LOAD-TIME-VALUE</span></i></a> '<span class="paren1">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/any_cons.html" class="symbol">CONS</a> <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">NIL</a> <a href="https://www.cliki.net/site/HyperSpec/Body/any_nil.html" class="symbol">NIL</a></span>)</span></span>)</span></span>)</span></span>)</span></span>)</span>
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<span class="paren3">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/mac_whencm_unless.html" class="symbol">UNLESS</a> <span class="paren4">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/acc_carcm_cdr_darcm_cddddr.html" class="symbol">CAR</a> MEMORY</span>)</span>
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<span class="paren4">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/any_setf.html" class="symbol">SETF</a> <span class="paren5">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/acc_carcm_cdr_darcm_cddddr.html" class="symbol">CDR</a> MEMORY</span>)</span> ,form</span>)</span>
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<span class="paren4">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/any_setf.html" class="symbol">SETF</a> <span class="paren5">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/acc_carcm_cdr_darcm_cddddr.html" class="symbol">CAR</a> MEMORY</span>)</span> <a href="https://www.cliki.net/site/HyperSpec/Body/any_t.html" class="symbol">T</a></span>)</span></span>)</span>
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<span class="paren3">(<span class="nonparen"><a href="https://www.cliki.net/site/HyperSpec/Body/acc_carcm_cdr_darcm_cddddr.html" class="symbol">CDR</a> MEMORY</span>)</span></span>)</span></span>)</span></span></div><p>You should probably be using either <a href="https://www.cliki.net/site/HyperSpec/Body/mac_defparametercm_defvar.html" class="hyperspec">DEFVAR</a>, <a href="https://www.cliki.net/site/HyperSpec/Body/speope_load-time-value.html" class="hyperspec">LOAD-TIME-VALUE</a>, or <a href="fare-memoization.html" class="internal">fare-memoization</a>:MEMOIZED-FUNCALL for local memoizations.<p><hr>
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