add for macro library

contrib/20.for/CMakeLists.txt

@@ -0,0 +1,2 @@
+file(GLOB FOR_FILES ${PROJECT_SOURCE_DIR}/contrib/20.for/piclib/*.scm)
+list(APPEND PICLIB_CONTRIB_LIBS ${FOR_FILES})

contrib/20.for/piclib/for.scm

@@ -0,0 +1,18 @@
+(define-library (picrin control list)
+  (import (scheme base)
+          (picrin control)
+          (scheme write))
+
+  (define-syntax for
+    (syntax-rules ()
+      ((_ expr)
+       (reset (lambda () expr)))))
+
+  (define (in m)
+    (shift (lambda (k)
+             (apply append (map k m)))))
+
+  (define (yield x)
+    (list x))
+
+  (export for in yield))