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comparison demo/prose @ 471:20fab0e96217

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Tree demo working (and other assorted regressions fixed)
author Adam Chlipala <adamc@hcoop.net>
date Thu, 06 Nov 2008 19:43:48 -0500
parents ddd363e856ff
children cbeb1683dc6a
comparison
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470:7cb418e9714f 471:20fab0e96217
130 130
131 metaform2.urp 131 metaform2.urp
132 132
133 <p>This example showcases code reuse by applying the same functor as in the last example. The <tt>Metaform2</tt> module mixes pages from the functor with some new pages of its own.</p> 133 <p>This example showcases code reuse by applying the same functor as in the last example. The <tt>Metaform2</tt> module mixes pages from the functor with some new pages of its own.</p>
134 134
135 tree.urp
136
137 <p>Here we see how we can abstract over common patterns of SQL queries. In particular, since standard SQL does not help much with queries over trees, we write a function for traversing an SQL tree, building an HTML representation, based on a user-provided function for rendering individual rows.</p>
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135 crud1.urp 139 crud1.urp
136 140
137 <p>This example pulls together much of what we have seen so far. It involves a generic "admin interface" builder. That is, we have the <tt>Crud.Make</tt> functor, which takes in a description of a table and outputs a sub-application for viewing and editing that table.</p> 141 <p>This example pulls together much of what we have seen so far. It involves a generic "admin interface" builder. That is, we have the <tt>Crud.Make</tt> functor, which takes in a description of a table and outputs a sub-application for viewing and editing that table.</p>
138 142
139 <p>The signature of <tt>Crud.Make</tt> is based around a type function <tt>colMeta</tt>, which describes which supporting values we need for each column. This function is declared with the keyword <tt>con</tt>, which stands for "constructor," the general class of "compile-time things" that includes types. An argument to <tt>colMeta</tt> has kind <tt>(Type * Type)</tt>, which means that it must be a type-level tuple. The first type is how the column is represented in SQL, and the second is how we represent it in HTML forms. In order, the components of the resulting record give: 143 <p>The signature of <tt>Crud.Make</tt> is based around a type function <tt>colMeta</tt>, which describes which supporting values we need for each column. This function is declared with the keyword <tt>con</tt>, which stands for "constructor," the general class of "compile-time things" that includes types. An argument to <tt>colMeta</tt> has kind <tt>(Type * Type)</tt>, which means that it must be a type-level tuple. The first type is how the column is represented in SQL, and the second is how we represent it in HTML forms. In order, the components of the resulting record give: