another sketch for refinement types

2 files changed, 102 insertions, 0 deletions

diff --git a/refined/value.go b/refined/value.go
new file mode 100644
index 0000000..cfaa412
--- /dev/null
+++ b/refined/value.go
@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: 2025 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package refined
+
+import (
+	"cmp"
+	"errors"
+	"regexp"
+
+	. "github.com/majewsky/gg/option"
+)
+
+type Scalar[S any, V any] struct {
+	value Option[V]
+}
+
+func (s Scalar[S, V]) Raw() V {
+	return s.value.UnwrapOrPanic("TODO 1")
+}
+
+func New[S IsAScalar[S, V], V any](value V) (S, error) {
+	var empty S
+	return empty.Refine(Challenge[S, V]{Value: value, valid: true})
+}
+
+func Literal[S IsAScalar[S, V], V any](value V) S {
+	var empty S
+	s, err := empty.Refine(Challenge[S, V]{Value: value, valid: true})
+	if err != nil {
+		panic("TODO 2")
+	}
+	return s
+}
+
+type IsAScalar[S any, V any] interface {
+	Refine(Challenge[S, V]) (S, error)
+}
+
+type Challenge[S any, V any] struct {
+	Value V
+	valid bool
+}
+
+func (c Challenge[S, V]) Accept() Scalar[S, V] {
+	if !c.valid {
+		panic("broken Challenge object")
+	}
+	return Scalar[S, V]{value: Some(c.Value)}
+}
+
+func RangeCheck[S any, V cmp.Ordered](c Challenge[S, V], minimum, maximum V) (Scalar[S, V], error) {
+	if minimum <= maximum && c.Value >= minimum && c.Value <= maximum {
+		return c.Accept(), nil
+	}
+	return Scalar[S, V]{}, errors.New("TODO 3")
+}
+
+func RegexpCheck[S any, V ~string](c Challenge[S, V], rx *regexp.Regexp) (Scalar[S, V], error) {
+	if rx.MatchString(string(c.Value)) {
+		return c.Accept(), nil
+	}
+	return Scalar[S, V]{}, errors.New("TODO 4")
+}
+
+func NotZeroCheck[S any, V comparable](c Challenge[S, V]) (Scalar[S, V], error) {
+	var zero V
+	if c.Value != zero {
+		return c.Accept(), nil
+	}
+	return Scalar[S, V]{}, errors.New("TODO 5")
+}
diff --git a/refined/value_test.go b/refined/value_test.go
new file mode 100644
index 0000000..aaf3706
--- /dev/null
+++ b/refined/value_test.go
@@ -0,0 +1,30 @@
+// SPDX-FileCopyrightText: 2025 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package refined_test
+
+import (
+	"testing"
+
+	. "github.com/majewsky/gg/internal/test"
+	"github.com/majewsky/gg/refined"
+)
+
+type DiceRoll struct {
+	refined.Scalar[DiceRoll, int]
+}
+
+func (DiceRoll) Refine(c refined.Challenge[DiceRoll, int]) (DiceRoll, error) {
+	s, err := refined.RangeCheck(c, 1, 6)
+	return DiceRoll{s}, err
+}
+
+func TestDiceRoll(t *testing.T) {
+	d := refined.Literal[DiceRoll](5)
+	AssertEqual(t, d.Raw(), 5)
+
+	var err error
+	d, err = refined.New[DiceRoll](7)
+	AssertEqual(t, d, DiceRoll{})
+	AssertEqual(t, err.Error(), "TODO 3")
+}