2 files changed, 122 insertions, 0 deletions
diff --git a/compiler/ast.go b/compiler/ast.go
index d4b8956..17054d0 100644
--- a/compiler/ast.go
+++ b/compiler/ast.go
@@ -260,6 +260,9 @@ func (n *concatNode) first() symbolPositionSet {
 func (n *concatNode) last() symbolPositionSet {
 	s := newSymbolPositionSet()
 	s.merge(n.right.last())
+	if n.right.nullable() {
+		s.merge(n.left.last())
+	}
 	return s
 }
 
diff --git a/compiler/ast_test.go b/compiler/ast_test.go
new file mode 100644
index 0000000..61d6064
--- /dev/null
+++ b/compiler/ast_test.go
@@ -0,0 +1,119 @@
+package compiler
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestASTNode(t *testing.T) {
+	tests := []struct {
+		root     astNode
+		nullable bool
+		first    symbolPositionSet
+		last     symbolPositionSet
+	}{
+		{
+			root:     newSymbolNode(nil, 0, 1),
+			nullable: false,
+			first:    newSymbolPositionSet().add(1),
+			last:     newSymbolPositionSet().add(1),
+		},
+		{
+			root:     newEndMarkerNode(1, 1),
+			nullable: false,
+			first:    newSymbolPositionSet().add(1),
+			last:     newSymbolPositionSet().add(1),
+		},
+		{
+			root: newConcatNode(
+				newSymbolNode(nil, 0, 1),
+				newSymbolNode(nil, 0, 2),
+			),
+			nullable: false,
+			first:    newSymbolPositionSet().add(1),
+			last:     newSymbolPositionSet().add(2),
+		},
+		{
+			root: newConcatNode(
+				newRepeatNode(newSymbolNode(nil, 0, 1)),
+				newSymbolNode(nil, 0, 2),
+			),
+			nullable: false,
+			first:    newSymbolPositionSet().add(1).add(2),
+			last:     newSymbolPositionSet().add(2),
+		},
+		{
+			root: newConcatNode(
+				newSymbolNode(nil, 0, 1),
+				newRepeatNode(newSymbolNode(nil, 0, 2)),
+			),
+			nullable: false,
+			first:    newSymbolPositionSet().add(1),
+			last:     newSymbolPositionSet().add(1).add(2),
+		},
+		{
+			root: newConcatNode(
+				newRepeatNode(newSymbolNode(nil, 0, 1)),
+				newRepeatNode(newSymbolNode(nil, 0, 2)),
+			),
+			nullable: true,
+			first:    newSymbolPositionSet().add(1).add(2),
+			last:     newSymbolPositionSet().add(1).add(2),
+		},
+		{
+			root: newAltNode(
+				newSymbolNode(nil, 0, 1),
+				newSymbolNode(nil, 0, 2),
+			),
+			nullable: false,
+			first:    newSymbolPositionSet().add(1).add(2),
+			last:     newSymbolPositionSet().add(1).add(2),
+		},
+		{
+			root: newAltNode(
+				newRepeatNode(newSymbolNode(nil, 0, 1)),
+				newSymbolNode(nil, 0, 2),
+			),
+			nullable: true,
+			first:    newSymbolPositionSet().add(1).add(2),
+			last:     newSymbolPositionSet().add(1).add(2),
+		},
+		{
+			root: newAltNode(
+				newSymbolNode(nil, 0, 1),
+				newRepeatNode(newSymbolNode(nil, 0, 2)),
+			),
+			nullable: true,
+			first:    newSymbolPositionSet().add(1).add(2),
+			last:     newSymbolPositionSet().add(1).add(2),
+		},
+		{
+			root: newAltNode(
+				newRepeatNode(newSymbolNode(nil, 0, 1)),
+				newRepeatNode(newSymbolNode(nil, 0, 2)),
+			),
+			nullable: true,
+			first:    newSymbolPositionSet().add(1).add(2),
+			last:     newSymbolPositionSet().add(1).add(2),
+		},
+		{
+			root:     newRepeatNode(newSymbolNode(nil, 0, 1)),
+			nullable: true,
+			first:    newSymbolPositionSet().add(1),
+			last:     newSymbolPositionSet().add(1),
+		},
+	}
+	for i, tt := range tests {
+		t.Run(fmt.Sprintf("#%v", i), func(t *testing.T) {
+			if tt.root.nullable() != tt.nullable {
+				t.Errorf("unexpected nullable attribute; want: %v, got: %v", tt.nullable, tt.root.nullable())
+			}
+			if tt.first.hash() != tt.root.first().hash() {
+				t.Errorf("unexpected first positions attribute; want: %v, got: %v", tt.first, tt.root.first())
+			}
+			if tt.last.hash() != tt.root.last().hash() {
+				t.Errorf("unexpected last positions attribute; want: %v, got: %v", tt.last, tt.root.last())
+			}
+		})
+	}
+}