Initial commit of modash

This was taken from github.com/lmika/gopkgs/fp

momap/fromslice.go

@@ -0,0 +1,30 @@
+package momap
+
+func FromSliceGroups[T any, K comparable](ts []T, fn func(t T) K) map[K][]T {
+	kvs := make(map[K][]T)
+	for _, t := range ts {
+		k := fn(t)
+		kvs[k] = append(kvs[k], t)
+	}
+	return kvs
+}
+
+func FromSlice[T any, K comparable, V any](ts []T, fn func(t T) (K, V)) map[K]V {
+	m, _ := FromSliceWithError(ts, func(t T) (k K, v V, _ error) {
+		k, v = fn(t)
+		return k, v, nil
+	})
+	return m
+}
+
+func FromSliceWithError[T any, K comparable, V any](ts []T, fn func(t T) (K, V, error)) (map[K]V, error) {
+	kvs := make(map[K]V)
+	for _, t := range ts {
+		k, v, err := fn(t)
+		if err != nil {
+			return nil, err
+		}
+		kvs[k] = v
+	}
+	return kvs, nil
+}