add (picrin procedure)

contrib/50.procedure/nitro.mk

@@ -0,0 +1 @@
+CONTRIB_LIBS += $(wildcard contrib/50.procedure/*.scm)

contrib/50.procedure/procedure.scm

@@ -0,0 +1,25 @@
+(define-library (picrin procedure)
+  (import (scheme base))
+  (export >>
+          <<
+          constant
+          identity)
+
+  (define identity values)
+
+  (define (constant . args)
+    (lambda _
+      (apply values args)))
+
+  (define (>> . fs)
+    (if (null? fs)
+        identity
+        (let ((f (car fs))
+              (g (apply >> (cdr fs))))
+          (lambda args
+            (call-with-values (lambda () (apply f args))
+              (lambda args
+                (apply g args)))))))
+
+  (define (<< . fs)
+    (apply >> (reverse fs))))