add type for filled samples & beta distribution

f.go

@@ -31,6 +31,19 @@ func (l Lognormal) Samples() []float64 {
 	return sample.Sample_parallel(sampler, 1_000_000)
 }
 
+type Beta struct {
+	a float64
+	b float64
+}
+
+type FilledSamples struct {
+	xs []float64
+}
+
+func (fs FilledSamples) Samples() []float64 {
+	return fs.xs
+}
+
 // Actually, I should look up how do do a) enums in go, b) union types
 /*type Lognormal struct {
 	low  float64