commit 6d06141751f158b3d1a2699f6e4bc5ddb635e19c
parent c0650a310a189c575512668182e19b8f136ceb53
Author: Greg Hendershott <greghendershott@gmail.com>
Date: Wed, 24 Oct 2012 20:23:13 -0400
Fix problem with syntax-parameterize.
Need to change order of examples so that `it` is still
undefined in the evaluator. (Is there a way to "reset"
the evaluator, for situation like this?)
Diffstat:
2 files changed, 12 insertions(+), 9 deletions(-)
diff --git a/index.html b/index.html
@@ -187,8 +187,10 @@ audience I’m writing for, you don’t know them yet. You can skip
learning them now. (Someday if you want to understand someone else’s
older macros, you can learn about them then.)</p></blockquote></blockquote></blockquote><p>The syntax variation of them works similarly. The idea is, we’ll
define <span class="RktSym">it</span> to mean an error by default. Only inside of our
-<span class="RktSym">aif</span> will it have a meaningful value:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">require</span><span class="hspace"> </span><span class="RktSym">racket/stxparam</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">define-syntax-parameter</span><span class="hspace"> </span><span class="RktSym">it</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lambda</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">raise-syntax-error</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">syntax-e</span><span class="hspace"> </span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">"can only be used inside aif"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">define-syntax-rule</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">aif</span><span class="hspace"> </span><span class="RktSym">condition</span><span class="hspace"> </span><span class="RktSym">true-expr</span><span class="hspace"> </span><span class="RktSym">false-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">let</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">tmp</span><span class="hspace"> </span><span class="RktSym">condition</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">if</span><span class="hspace"> </span><span class="RktSym">tmp</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">syntax-parameterize</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">it</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-rename-transformer</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym">tmp</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktSym">true-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktSym">false-expr</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">aif</span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">displayln</span><span class="hspace"> </span><span class="RktSym">it</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">void</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">10</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">aif</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">displayln</span><span class="hspace"> </span><span class="RktSym">it</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">void</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>We can still use <span class="RktSym">it</span> as a normal variable name:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">define</span><span class="hspace"> </span><span class="RktSym">it</span><span class="hspace"> </span><span class="RktVal">10</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktSym">it</span></td></tr><tr><td><p><span class="RktRes">10</span></p></td></tr></table></blockquote><p>If we try to use <span class="RktSym">it</span> outside of an <span class="RktSym">aif</span> form, and
-<span class="RktSym">it</span> isn’t otherwise defined, we get an error like we want:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">displayln</span><span class="hspace"> </span><span class="RktSym">it</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">10</span></p></td></tr></table></blockquote><p>Perfect.</p><h3>6<tt> </tt><a name="(part._.Robust_macros__syntax-parse)"></a>Robust macros: syntax-parse</h3><p>TO-DO.</p><h3>7<tt> </tt><a name="(part._.Other_questions)"></a>Other questions</h3><p>Hopefully I will answer these in the course of the other sections. But
+<span class="RktSym">aif</span> will it have a meaningful value:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">require</span><span class="hspace"> </span><span class="RktSym">racket/stxparam</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">define-syntax-parameter</span><span class="hspace"> </span><span class="RktSym">it</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lambda</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">stx</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">raise-syntax-error</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">syntax-e</span><span class="hspace"> </span><span class="RktSym">stx</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">"can only be used inside aif"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">define-syntax-rule</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">aif</span><span class="hspace"> </span><span class="RktSym">condition</span><span class="hspace"> </span><span class="RktSym">true-expr</span><span class="hspace"> </span><span class="RktSym">false-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">let</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">tmp</span><span class="hspace"> </span><span class="RktSym">condition</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">if</span><span class="hspace"> </span><span class="RktSym">tmp</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">syntax-parameterize</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">it</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-rename-transformer</span><span class="hspace"> </span><span class="RktRdr">#'</span><span class="RktSym">tmp</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktSym">true-expr</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPlain"><span class="hspace"> </span></span><span class="hspace"> </span><span class="RktSym">false-expr</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">aif</span><span class="hspace"> </span><span class="RktVal">10</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">displayln</span><span class="hspace"> </span><span class="RktSym">it</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">void</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">10</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">aif</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">displayln</span><span class="hspace"> </span><span class="RktSym">it</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">void</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote><p>If we try to use <span class="RktSym">it</span> outside of an <span class="RktSym">aif</span> form, and
+<span class="RktSym">it</span> isn’t otherwise defined, we get an error like we want:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">displayln</span><span class="hspace"> </span><span class="RktSym">it</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktErr">it: can only be used inside aif</span></p></td></tr></table></blockquote><p>But we can still define <span class="RktSym">it</span> as a normal variable:</p><blockquote class="SCodeFlow"><table cellspacing="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">define</span><span class="hspace"> </span><span class="RktSym">it</span><span class="hspace"> </span><span class="RktVal">10</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktSym">it</span></td></tr><tr><td><p><span class="RktRes">10</span></p></td></tr></table></blockquote><h3>6<tt> </tt><a name="(part._.Robust_macros__syntax-parse)"></a>Robust macros: syntax-parse</h3><p>TO-DO.
+TO-DO.
+TO-DO.</p><h3>7<tt> </tt><a name="(part._.Other_questions)"></a>Other questions</h3><p>Hopefully I will answer these in the course of the other sections. But
just in case:</p><h4>7.1<tt> </tt><a name="(part._.What_s_the_point_of_with-syntax_)"></a>What’s the point of <span class="RktSym">with-syntax</span>?</h4><p>Done.</p><h4>7.2<tt> </tt><a name="(part._.What_s_the_point_of_begin-for-syntax_)"></a>What’s the point of <span class="RktSym">begin-for-syntax</span>?</h4><p>TO-DO.</p><h4>7.3<tt> </tt><a name="(part._.What_s_the_point_of_racket_splicing_)"></a>What’s the point of <span class="RktSym">racket/splicing</span>?</h4><p>TO-DO.</p><h3>8<tt> </tt><a name="(part._.References_.Acknowledgments)"></a>References/Acknowledgments</h3><p>Eli Barzliay wrote a blog post,
<a href="http://blog.racket-lang.org/2011/04/writing-syntax-case-macros.html">Writing
‘syntax-case’ Macros</a>, which explains many key details. However it’s written
diff --git a/main.rkt b/main.rkt
@@ -724,27 +724,28 @@ define @racket[it] to mean an error by default. Only inside of our
(aif #f (displayln it) (void))
]
-We can still use @racket[it] as a normal variable name:
+If we try to use @racket[it] outside of an @racket[aif] form, and
+@racket[it] isn't otherwise defined, we get an error like we want:
@i[
-(define it 10)
-it
+(displayln it)
]
-If we try to use @racket[it] outside of an @racket[aif] form, and
-@racket[it] isn't otherwise defined, we get an error like we want:
+But we can still define @racket[it] as a normal variable:
@i[
-(displayln it)
+(define it 10)
+it
]
-Perfect.
@; ----------------------------------------------------------------------------
@section{Robust macros: syntax-parse}
TO-DO.
+TO-DO.
+TO-DO.
@; ----------------------------------------------------------------------------
