implemented Empty in seq

seq/seq.go

@@ -44,6 +44,13 @@ func Size(s Seq) uint64 {
 	}
 }
 
+// Returns whether or not the given Seq is empty. This is accomplished using
+// FirstRest and NOT just by naively returning Size(s) == 0.
+func Empty(s Seq) bool {
+	_, _, ok := s.FirstRest()
+	return !ok
+}
+
 // Returns the elements in the Seq as a slice. If the underlying Seq has any
 // implicit order to it that order will be kept. An empty Seq will return an
 // empty slice; nil is never returned. In general this completes in O(N) time.

seq/seq_test.go

@@ -6,7 +6,7 @@ import (
 	"github.com/mediocregopher/ginger/types"
 )
 
-// Tests the FirstRest, Size, and ToSlice methods of a Seq
+// Tests the FirstRest, Size, Empty, and ToSlice methods of a Seq
 func testSeqGen(t *T, s Seq, ints []types.Elem) Seq {
 	intsl := uint64(len(ints))
 	for i := range ints {
@@ -18,8 +18,13 @@ func testSeqGen(t *T, s Seq, ints []types.Elem) Seq {
 		assertValue(ok, true, t)
 		assertValue(first, ints[i], t)
 
+		empty := Empty(s)
+		assertValue(empty, false, t)
+
 		s = rest
 	}
+	empty := Empty(s)
+	assertValue(empty, true, t)
 	return s
 }