Move examples.scm to directory.

1 files changed, 41 insertions, 0 deletions

diff --git a/examples/do.scm b/examples/do.scm
new file mode 100644
index 0000000..d758177
--- /dev/null
+++ b/examples/do.scm
@@ -0,0 +1,41 @@
+(add-to-load-path (dirname (current-filename)))
+
+(use-modules (control monad)
+             (data monoid)
+             (data optional)
+             (data writer))
+
+;;; Optional Monad, and do notation
+
+(do x <- (just 10)
+    x) ; => 10
+
+(do let y = (just 10)
+    x <- y
+    (+ x 5)) ; => 15
+
+(do x <- (nothing)
+    (+ x 5)) ; => [Nothing]
+
+(do x <- (just 10)
+    y <- (just 20)
+    (+ x y)) ; => 30
+
+(do (just 10)
+    (nothing)
+  (just 20)) ; => [Nothing]
+
+;;; Writer Monad, and do notation
+
+;; Int -> Writer Int String
+(define (log-number n)
+  (writer n (format #f "Got nuber: ~a" n)))
+
+(do a <- (log-number 3)
+    b <- (log-number 5)
+    (writer (* a b) ""))
+;; => [Writer 15, "Got nuber: 3Got nuber: 5"]
+
+(do (log-number 3)
+    (log-number 5))
+;; => [Writer 5, "Got nuber: 3Got nuber: 5"]