New Post: A Quick Pollen Macro (for/s)

posts/a-quick-pollen-macro.poly.pm

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+#lang pollen
+
+◊(define-meta title "A Quick Pollen Macro")
+◊(define-meta published "2018-07-07")
+◊(define-meta topics "Pollen")
+
+One of Pollen’s
+◊link["https://groups.google.com/d/msg/pollenpub/FdWdGgL9jSk/1VWpX_nsAAAJ"]{somewhat recent}
+additions is the ◊link["http://docs.racket-lang.org/pollen/Core.html#%28form._%28%28lib._pollen%2Fcore..rkt%29._for%2Fsplice%29%29"]{◊code{for/splice}} function,
+which lets you loop through one or more lists
+and inject the results into a surrounding expression.
+
+Here’s an example from the code for the home page on this blog:
+
+◊blockcode[#:filename "index.html.pp"]{...
+◊"◊"for/splice[[(post (in-list (latest-posts 10)))]]{
+   <article>
+   ◊"◊"(hash-ref post 'header_html)
+   ◊"◊"(hash-ref post 'html)
+   </article>
+   <hr>
+}
+...}
+
+It’s very useful,
+but I’m sure you’ve noticed something about this code:
+◊emph{many many parentheses} 
+in the arguments list for ◊code{for/splice}.
+Well, it is the way it is,
+because the ◊code{for/splice} function 
+is a direct analogue
+of Racket’s ◊link["https://docs.racket-lang.org/reference/for.html?q=for%2Flist#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._for%2Flist%29%29"]{◊code{for/list} function},
+which supports looping through multiple lists at the same time.
+It’s nice to have the flexibility.
+But there’s no denying the readability of the code suffers
+in the most common use cases.
+
+If, like me, you usually only need to loop through a single list,
+you can put a macro like the one below 
+in your ◊code{pollen.rkt}:
+
+◊blockcode[#:filename "pollen.rkt"]{
+(require pollen/core)
+
+...
+
+(provide for/s)
+(define-syntax (for/s stx)
+  (syntax-case stx ()
+    [(_ thing listofthings result-expr ...)
+     #'(for/splice ([thing (in-list listofthings)]) result-expr ...)]))
+}
+
+This cuts down on the parentheses quite a bit:
+
+◊blockcode[#:filename "index.html.pp"]{...
+◊"◊"for/s[post (latest-posts 10)]{
+   <article>
+   ◊"◊"(hash-ref post 'header_html)
+   ◊"◊"(hash-ref post 'html)
+   </article>
+   <hr>
+}
+...}
+