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+;;; CHICKEN-SCRATCH --- heredocs for CHICKEN
+;; written by Case Duckworth <acdw@acdw.net> off an idea by evhan
+;; Licensed under BSD-3.  See COPYING for details.
+
+;; CHICKEN has "Multiline string constants with embedded expressions" syntax,
+;; which is basically shell here-doc syntax but schemier and with a real
+;; programming langugage to embed. evhan's beaker tool (which is great, btw)
+;; uses this facility to do a quick-and-dirty templating for wiki generation. I
+;; realized that I could use the same facility for the same kind of
+;; heredoc-style templating I have done in various other SSGs like unk and
+;; vienna, but with scheme. Thus, CHICKEN-SCRATCH was born.
+
+;; USAGE
+
+;; `expand-string' is the main entry point to this module. It takes a string and
+;; returns a string with all #( ... ) forms expanded according to the CHICKEN
+;; rules. `expand-port' is a port version of `expand-string'.
+
+;; To enable truly invisible definitions within the expanded string, the `def'
+;; macro is provided which performs a `set!' on its variables, then returns a
+;; string guaranteed not to be in the input string, which is then filtered out
+;; in the expanded string.
+
+;; Finally, to enable CHICKEN-SCRATCH to be used in a shebang, if the first line
+;; of the input string begins with #!, it's deleted from the input.
+
+(module chicken-scratch
+    (expand-string
+     expand-port
+     def
+     %def/replacer)
+
+  (import scheme
+          (chicken base)
+          (only (chicken io)
+                read-string)
+          (only (chicken irregex)
+                irregex-replace
+                irregex-replace/all
+                irregex-search)
+          (only (chicken port)
+                make-concatenated-port)
+          (only (chicken random)
+                pseudo-random-real))
+
+  (define %def/replacer (make-parameter #f))
+
+  (define (expand-string str)
+    (parameterize ((%def/replacer (random-string-not-in str)))
+      (let* ((delim (random-string-not-in str))
+             (template (make-concatenated-port
+                        (open-input-string (string-append "#<#" delim "\n"))
+                        (open-input-string (irregex-replace "^#!.*\n" str ""))
+                        (open-input-string (string-append "\n" delim "\n"))))
+             (expanded (open-output-string))
+             (output (begin
+                       (display (eval (read template)) expanded)
+                       (get-output-string expanded))))
+        (irregex-replace/all `(seq ,(%def/replacer) (* "\n"))
+                             output
+                             ""))))
+
+  (define (expand-port #!optional port)
+    (let ((port (or port (current-input-port))))
+      (expand-string (read-string #f port))))
+
+  (define-syntax def
+    (syntax-rules ()
+      ((def var val)
+       ;; I think this only works in CHICKEN.
+       (begin (set! var val)
+              (%def/replacer)))))
+
+  (define (random-string-not-in str)
+    (let ((attempt (number->string (pseudo-random-real))))
+      (if (irregex-search attempt str)
+          (random-string-not-in str)
+          attempt))))