Support for bind to map values

ref: #569

```yaml
bind:
  vars:
    "foo[i]": current.res
```

bind.go

@@ -3,7 +3,11 @@ package runn
 import (
 	"context"
 	"fmt"
+	"sort"
+	"strings"
 
+	"github.com/antonmedv/expr/ast"
+	"github.com/antonmedv/expr/parser"
 	"github.com/samber/lo"
 )
 
@@ -26,18 +30,224 @@ func (rnr *bindRunner) Run(ctx context.Context, s *step, first bool) error {
 		store[storeRootPrevious] = o.store.previous()
 		store[storeRootKeyCurrent] = o.store.latest()
 	}
-	for k, v := range cond {
+	keys := lo.Keys(cond)
+	sort.Slice(keys, func(i, j int) bool {
+		return keys[i] < keys[j]
+	})
+	for _, k := range keys {
 		if lo.Contains(reservedStoreRootKeys, k) {
 			return fmt.Errorf("%q is reserved", k)
 		}
-		vv, err := EvalAny(v, store)
+		v := cond[k]
+		kv, err := evalBindKeyValue(o.store.bindVars, k, v, store)
 		if err != nil {
 			return err
 		}
-		o.store.bindVars[k] = vv
+		o.store.bindVars = kv
 	}
 	if first {
 		o.record(nil)
 	}
 	return nil
 }
+
+func evalBindKeyValue(bindVars map[string]any, k string, v any, store map[string]any) (map[string]any, error) {
+	vv, err := EvalAny(v, store)
+	if err != nil {
+		return nil, err
+	}
+	if !strings.Contains(k, "[") || !strings.HasSuffix(k, "]") {
+		// Override the value of bindVars
+		bindVars[k] = vv
+		return bindVars, nil
+	}
+	// Merge the value of bindVars
+	// foo[bar]
+	// foo['bar']
+	// foo[5]
+	// foo[bar][baz]
+	tr, err := parser.Parse(k)
+	if err != nil {
+		return nil, err
+	}
+	kv, err := nodeToMap(tr.Node, vv, store)
+	if err != nil {
+		return nil, err
+	}
+	return mergeVars(bindVars, kv), nil
+}
+
+func nodeToMap(n ast.Node, v any, store map[string]any) (map[string]any, error) {
+	m := map[string]any{}
+	switch nn := n.(type) {
+	case *ast.MemberNode:
+		switch nnn := nn.Node.(type) {
+		case *ast.IdentifierNode:
+			k := nnn.Value
+			switch p := nn.Property.(type) {
+			case *ast.IdentifierNode:
+				kk, err := EvalAny(p.Value, store)
+				if err != nil {
+					return nil, err
+				}
+				if kk == nil {
+					return nil, fmt.Errorf("invalid value: %v", p.Value)
+				}
+				m[k] = map[any]any{
+					kk: v,
+				}
+			case *ast.StringNode:
+				m[k] = map[any]any{
+					p.Value: v,
+				}
+			case *ast.IntegerNode:
+				m[k] = map[any]any{
+					p.Value: v,
+				}
+			case *ast.MemberNode:
+				kk, err := EvalAny(p.String(), store)
+				if err != nil {
+					return nil, err
+				}
+				if kk == nil {
+					return nil, fmt.Errorf("invalid value: %v", p.String())
+				}
+				m[k] = map[any]any{
+					kk: v,
+				}
+			default:
+				return nil, fmt.Errorf("invalid node type of %v: %T", nn.Property, nn.Property)
+			}
+		case *ast.MemberNode:
+			vv := map[any]any{}
+			switch p := nn.Property.(type) {
+			case *ast.IdentifierNode:
+				kk, err := EvalAny(p.Value, store)
+				if err != nil {
+					return nil, err
+				}
+				if kk == nil {
+					return nil, fmt.Errorf("invalid value: %v", p.Value)
+				}
+				vv = map[any]any{
+					kk: v,
+				}
+			case *ast.StringNode:
+				vv = map[any]any{
+					p.Value: v,
+				}
+			case *ast.IntegerNode:
+				vv = map[any]any{
+					p.Value: v,
+				}
+			case *ast.MemberNode:
+				kk, err := EvalAny(p.String(), store)
+				if err != nil {
+					return nil, err
+				}
+				if kk == nil {
+					return nil, fmt.Errorf("invalid value: %v", p.String())
+				}
+				vv = map[any]any{
+					kk: v,
+				}
+			default:
+				return nil, fmt.Errorf("invalid node type of %v: %T", nn.Property, nn.Property)
+			}
+			vvv, err := nodeToMap(nnn, vv, store)
+			if err != nil {
+				return nil, err
+			}
+			m = vvv
+		}
+	default:
+		return nil, fmt.Errorf("invalid node type of %v: %T", n, n)
+	}
+	return m, nil
+}
+
+func mergeVars(store map[string]any, vars map[string]any) map[string]any {
+	for k, v := range vars {
+		sv, ok := store[k]
+		if !ok {
+			store[k] = v
+			continue
+		}
+		switch svv := sv.(type) {
+		case map[string]any:
+			switch vv := v.(type) {
+			case map[string]any:
+				store[k] = mergeVars(svv, vv)
+			case map[any]any:
+				// convert svv map[string]any to map[any]any
+				svv2 := make(map[any]any)
+				for k, v := range svv {
+					svv2[k] = v
+				}
+				store[k] = mergeMapAny(svv2, vv)
+			default:
+				store[k] = vv
+			}
+		case map[any]any:
+			switch vv := v.(type) {
+			case map[string]any:
+				// convert vv map[string]any to map[any]any
+				vv2 := make(map[any]any)
+				for k, v := range vv {
+					vv2[k] = v
+				}
+				store[k] = mergeMapAny(svv, vv2)
+			case map[any]any:
+				store[k] = mergeMapAny(svv, vv)
+			default:
+				store[k] = vv
+			}
+		case []any:
+			switch vv := v.(type) {
+			case []any:
+				store[k] = append(svv, vv...)
+			default:
+				store[k] = vv
+			}
+		default:
+			store[k] = v
+		}
+	}
+	return store
+}
+
+func mergeMapAny(store map[any]any, vars map[any]any) map[any]any {
+	for k, v := range vars {
+		sv, ok := store[k]
+		if !ok {
+			store[k] = v
+			continue
+		}
+		switch svv := sv.(type) {
+		case map[string]any:
+			switch vv := v.(type) {
+			case map[string]any:
+				store[k] = mergeVars(svv, vv)
+			default:
+				store[k] = vv
+			}
+		case map[any]any:
+			switch vv := v.(type) {
+			case map[any]any:
+				store[k] = mergeMapAny(svv, vv)
+			default:
+				store[k] = vv
+			}
+		case []any:
+			switch vv := v.(type) {
+			case []any:
+				store[k] = append(svv, vv...)
+			default:
+				store[k] = vv
+			}
+		default:
+			store[k] = v
+		}
+	}
+	return store
+}