diff --git a/src/lib.rs b/src/lib.rs
index 13872a3d9a..d95e266624 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,6 @@ mod parser;
 
 pub mod syntax_kinds;
 pub use text::{TextUnit, TextRange};
-pub use tree::{SyntaxKind, Token, FileBuilder, File, Node};
+pub use tree::{SyntaxKind, Token, FileBuilder, Sink, File, Node};
 pub use lexer::{next_token, tokenize};
 pub use parser::parse;
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index 7336c51363..0a136266cc 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -1,4 +1,4 @@
-use {Token, File, FileBuilder};
+use {Token, File, FileBuilder, Sink};
 
 use syntax_kinds::*;
 
diff --git a/src/tree/file_builder.rs b/src/tree/file_builder.rs
index 430303ce93..eba850fef0 100644
--- a/src/tree/file_builder.rs
+++ b/src/tree/file_builder.rs
@@ -1,6 +1,13 @@
 use {SyntaxKind, TextUnit, TextRange};
 use super::{NodeData, NodeIdx, File};
 
+pub trait Sink {
+    fn leaf(&mut self, kind: SyntaxKind, len: TextUnit);
+    fn start_internal(&mut self, kind: SyntaxKind);
+    fn finish_internal(&mut self);
+}
+
+
 pub struct FileBuilder {
     text: String,
     nodes: Vec<NodeData>,
@@ -8,6 +15,44 @@ pub struct FileBuilder {
     pos: TextUnit,
 }
 
+impl Sink for FileBuilder {
+    fn leaf(&mut self, kind: SyntaxKind, len: TextUnit) {
+        let leaf = NodeData {
+            kind,
+            range: TextRange::from_len(self.pos, len),
+            parent: None,
+            first_child: None,
+            next_sibling: None,
+        };
+        self.pos += len;
+        let id = self.push_child(leaf);
+        self.add_len(id);
+    }
+
+    fn start_internal(&mut self, kind: SyntaxKind) {
+        let node = NodeData {
+            kind,
+            range: TextRange::from_len(self.pos, 0.into()),
+            parent: None,
+            first_child: None,
+            next_sibling: None,
+        };
+        let id = if self.in_progress.is_empty() {
+            self.new_node(node)
+        } else {
+            self.push_child(node)
+        };
+        self.in_progress.push((id, None))
+    }
+
+    fn finish_internal(&mut self) {
+        let (id, _) = self.in_progress.pop().unwrap();
+        if !self.in_progress.is_empty() {
+            self.add_len(id);
+        }
+    }
+}
+
 impl FileBuilder {
     pub fn new(text: String) -> FileBuilder {
         FileBuilder {
@@ -27,42 +72,6 @@ impl FileBuilder {
         }
     }
 
-    pub fn leaf(&mut self, kind: SyntaxKind, len: TextUnit) {
-        let leaf = NodeData {
-            kind,
-            range: TextRange::from_len(self.pos, len),
-            parent: None,
-            first_child: None,
-            next_sibling: None,
-        };
-        self.pos += len;
-        let id = self.push_child(leaf);
-        self.add_len(id);
-    }
-
-    pub fn start_internal(&mut self, kind: SyntaxKind) {
-        let node = NodeData {
-            kind,
-            range: TextRange::from_len(self.pos, 0.into()),
-            parent: None,
-            first_child: None,
-            next_sibling: None,
-        };
-        let id = if self.in_progress.is_empty() {
-            self.new_node(node)
-        } else {
-            self.push_child(node)
-        };
-        self.in_progress.push((id, None))
-    }
-
-    pub fn finish_internal(&mut self) {
-        let (id, _) = self.in_progress.pop().unwrap();
-        if !self.in_progress.is_empty() {
-            self.add_len(id);
-        }
-    }
-
     fn new_node(&mut self, data: NodeData) -> NodeIdx {
         let id = NodeIdx(self.nodes.len() as u32);
         self.nodes.push(data);
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index 6bacb46eff..7a5d429a37 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -4,7 +4,7 @@ use syntax_kinds::syntax_info;
 use std::fmt;
 
 mod file_builder;
-pub use self::file_builder::FileBuilder;
+pub use self::file_builder::{FileBuilder, Sink};
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct SyntaxKind(pub(crate) u32);