Data commit

Task/Monads-Maybe-monad/Go/monads-maybe-monad.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+    "fmt"
+    "strconv"
+)
+
+type maybe struct{ value *int }
+
+func (m maybe) bind(f func(p *int) maybe) maybe {
+    return f(m.value)
+}
+
+func unit(p *int) maybe {
+    return maybe{p}
+}
+
+func decrement(p *int) maybe {
+    if p == nil {
+        return unit(nil)
+    } else {
+        q := *p - 1
+        return unit(&q)
+    }
+}
+
+func triple(p *int) maybe {
+    if p == nil {
+        return unit(nil)
+    } else {
+        q := (*p) * 3
+        return unit(&q)
+    }
+}
+
+func main() {
+    i, j, k := 3, 4, 5
+    for _, p := range []*int{&i, &j, nil, &k} {
+        m1 := unit(p)
+        m2 := m1.bind(decrement).bind(triple)
+        var s1, s2 string = "none", "none"
+        if m1.value != nil {
+            s1 = strconv.Itoa(*m1.value)
+        }
+        if m2.value != nil {
+            s2 = strconv.Itoa(*m2.value)
+        }
+        fmt.Printf("%4s -> %s\n", s1, s2)
+    }
+}