Fix SliceNode String()

ast/print.go

@@ -94,6 +94,15 @@ func (n *MemberNode) String() string {
 }
 
 func (n *SliceNode) String() string {
+	if n.From == nil && n.To == nil {
+		return fmt.Sprintf("%s[:]", n.Node.String())
+	}
+	if n.From == nil {
+		return fmt.Sprintf("%s[:%s]", n.Node.String(), n.To.String())
+	}
+	if n.To == nil {
+		return fmt.Sprintf("%s[%s:]", n.Node.String(), n.From.String())
+	}
 	return fmt.Sprintf("%s[%s:%s]", n.Node.String(), n.From.String(), n.To.String())
 }
 

ast/print_test.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/antonmedv/expr/ast"
 	"github.com/antonmedv/expr/parser"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -63,14 +64,16 @@ func TestPrint(t *testing.T) {
 		{`a.b()`, `a.b()`},
 		{`a.b(c)`, `a.b(c)`},
 		{`a[1:-1]`, `a[1:-1]`},
+		{`a[1:]`, `a[1:]`},
+		{`a[1:]`, `a[1:]`},
+		{`a[:]`, `a[:]`},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.input, func(t *testing.T) {
 			tree, err := parser.Parse(tt.input)
 			require.NoError(t, err)
-
-			require.Equal(t, tt.want, tree.Node.String())
+			assert.Equal(t, tt.want, tree.Node.String())
 		})
 	}
 }