implement comma in Sex sources

Readme.org

@@ -1,18 +1,20 @@
 * The Sex language
 Sex is a S-expressions language, which transpiles to C.
 
-* Compilation and usage
-Sex is written in Chicken Scheme, so first you'll need to get yourself
-a Chicken.
+Sex is also Chicken, since all source processing and compile-time
+computations are written in Chicken.
 
-It also has a couple of Chicken deps.
+And Chicken is R5RS Scheme.
+
+* Compilation and usage
+First, get yourself a Chicken. Second, one Chicken deps.
 
 ** Install Chicken Eggs
 By the way, there's a way to make Chicken install eggs non-globally. Refer to
 the documentation for more info:
 https://wiki.call-cc.org/man/5/Extension%20tools#changing-the-repository-location
 
-~chicken-install fmt tree brev-separate~
+~chicken-install fmt~
 
 ** Compilation
 ~make~
@@ -24,6 +26,43 @@ cat hello-world.sex | sexc > hello_world.c
 cc hello_world.c -o hello_world
 #+end_src
 
+* Example
+Here is an example, demonstrating what Sex source looks like, and what
+it compiles too. An avid reader also shall notice how we call Chicken
+procedures in Sex source.
+
+The Sex source:
+#+begin_src
+(include stdio.h)
+
+(define (foo)
+  "Hello from Chicken code!\n")
+
+(fn int main ((int argc) (char **argv))
+    (puts "Hello from Sex!")
+    (var (array char 512) name)
+    (puts "What is your name?")
+    (scanf "%s" &name)
+    (printf "Hello, %s!\n" name)
+    (printf ,(foo))
+    0)
+#+end_src
+
+The resulting C source:
+#+begin_src
+#include <stdio.h>
+
+int main (int argc, char **argv) {
+    puts("Hello from Sex!");
+    char name[512];
+    puts("What is your name?");
+    scanf("%s", &name);
+    printf("Hello, %s!\n", name);
+    printf("Hello from Chicken code!\n");
+    return 0;
+}
+#+end_src
+
 * Features
 ** Full C interoperability
 Just ~(include "Your/Favourite/Library.h")~ and use it as you would

hello-world.sex

@@ -1,10 +1,13 @@
 (include stdio.h)
-(include unistd.h)
+
+(define (foo)
+  "Hello from Chicken code!\n")
 
 (fn int main ((int argc) (char **argv))
     (puts "Hello from Sex!")
-    (var (array char 513) name)
+    (var (array char 512) name)
     (puts "What is your name?")
     (scanf "%s" &name)
     (printf "Hello, %s!\n" name)
+    (printf ,(foo))
     0)

sexc.scm

@@ -1,19 +1,35 @@
-(import brev-separate fmt fmt-c tree (chicken string))
+(import fmt fmt-c (chicken string))
 
 (define (unkebabify sym)
   (string->symbol
    (string-translate (symbol->string sym) #\- #\_)))
 
-(define (loop)
-  (let ((r (read)))
-    (unless (eof-object? r)
-      (cond ((eqv? (car r) 'define) (eval r))
-            (#t
-             (fmt #t
-                  (c-expr
-                   (tree-map
-                    (fn
-	             (case x
+(define (map-filter-tree map-proc filter-proc tree)
+  "Walk the tree, checking each element with filter-proc.
+If filter-proc returns #t:
+  - if the element is list, process it recursively,
+  - if the element is an atom, process it with map-proc.
+
+If filter-proc returns #f, ignore the element.
+
+If filter-proc returns something other, use it instead of processing the element."
+  (let ((cont (cut map-filter-tree map-proc filter-proc <>)))
+    (if (null? tree) '()
+        (let ((filter-res (filter-proc (car tree))))
+          ;(fmt #t "Filter res for " tree " is " filter-res "\n")
+          (case filter-res
+            ((#t) (cons
+                   (if (atom? (car tree))
+                       (map-proc (car tree))
+                       (cont (car tree)))
+                   (cont (cdr tree))))
+            ((#f) (cont (cdr tree)))
+            (else (cons filter-res (cont (cdr tree)))))))))
+
+(define (walk-tree tree)
+  (map-filter-tree
+   (lambda (elem)
+     (case elem
        ((fn) '%fun)
        ((var) '%var)
        ((begin) '%begin)
@@ -23,11 +39,33 @@
        ((include) '%include)
        ((cast) '%cast)
        (else
-                        (if (symbol? x)
-                            (unkebabify x)
-                            x))))
-                    r)))
-             (fmt #t "\n")))
-      (loop))))
+        (if (symbol? elem)
+            (unkebabify elem)
+            elem))))
+   (lambda (subtree)
+     (if (list? subtree)
+         (case (car subtree)
+           ((unquote)
+            (eval (cadr subtree)))
+           (else #t))
+         #t))
+   tree))
+
+(define (loop)
+  (call/cc
+   (lambda (return)
+     (let ((r (read)))
+       (when (eof-object? r)
+         (return '()))
+       (case (car r)
+         ((define)
+          (eval r)
+          (fmt #t "\n"))
+         (else
+          (let ((result (walk-tree r)))
+            (when result
+              (fmt #t (c-expr
+                       result))))))
+       (loop)))))
 
 (loop)