diff --git a/crates/fuse-parser/tests/cases/pass/function-declaration-02/ast.snap b/crates/fuse-parser/tests/cases/pass/function-declaration-02/ast.snap
new file mode 100644
index 0000000..3eed0ab
--- /dev/null
+++ b/crates/fuse-parser/tests/cases/pass/function-declaration-02/ast.snap
@@ -0,0 +1,100 @@
+---
+source: crates/fuse-parser/tests/cases/mod.rs
+expression: parsed.chunk
+input_file: crates/fuse-parser/tests/cases/pass/function-declaration-02/case.fuse
+---
+Some(Chunk(
+  span: Span(
+    start: 0,
+    end: 31,
+  ),
+  body: Block(
+    statements: [
+      FunctionDeclaration(Function(
+        span: Span(
+          start: 0,
+          end: 26,
+        ),
+        identifier: Some(Identifier(
+          span: Span(
+            start: 9,
+            end: 13,
+          ),
+          name: Atom("test"),
+        )),
+        params: FunctionParameters(
+          span: Span(
+            start: 13,
+            end: 23,
+          ),
+          items: [
+            FunctionParameter(
+              span: Span(
+                start: 14,
+                end: 15,
+              ),
+              pattern: BindingPattern(
+                kind: Identifier(BindingIdentifier(
+                  span: Span(
+                    start: 14,
+                    end: 15,
+                  ),
+                  atom: Atom("a"),
+                )),
+                type_annotation: None,
+                optional: false,
+              ),
+            ),
+            FunctionParameter(
+              span: Span(
+                start: 17,
+                end: 18,
+              ),
+              pattern: BindingPattern(
+                kind: Identifier(BindingIdentifier(
+                  span: Span(
+                    start: 17,
+                    end: 18,
+                  ),
+                  atom: Atom("b"),
+                )),
+                type_annotation: None,
+                optional: false,
+              ),
+            ),
+            FunctionParameter(
+              span: Span(
+                start: 20,
+                end: 21,
+              ),
+              pattern: BindingPattern(
+                kind: Identifier(BindingIdentifier(
+                  span: Span(
+                    start: 20,
+                    end: 21,
+                  ),
+                  atom: Atom("c"),
+                )),
+                type_annotation: None,
+                optional: false,
+              ),
+            ),
+          ],
+          rest: None,
+        ),
+        return_type: None,
+        body: Block(Block(
+          statements: [
+            Expression(Identifier(Identifier(
+              span: Span(
+                start: 25,
+                end: 26,
+              ),
+              name: Atom("b"),
+            ))),
+          ],
+        )),
+      )),
+    ],
+  ),
+))
diff --git a/crates/fuse-parser/tests/cases/pass/function-declaration-02/case.fuse b/crates/fuse-parser/tests/cases/pass/function-declaration-02/case.fuse
new file mode 100644
index 0000000..9a21252
--- /dev/null
+++ b/crates/fuse-parser/tests/cases/pass/function-declaration-02/case.fuse
@@ -0,0 +1,3 @@
+function test(a, b, c,)
+	b
+end
diff --git a/crates/fuse-parser/tests/cases/pass/function-declaration-02/tokens.snap b/crates/fuse-parser/tests/cases/pass/function-declaration-02/tokens.snap
new file mode 100644
index 0000000..dafc3d2
--- /dev/null
+++ b/crates/fuse-parser/tests/cases/pass/function-declaration-02/tokens.snap
@@ -0,0 +1,187 @@
+---
+source: crates/fuse-parser/tests/cases/mod.rs
+expression: tokens
+input_file: crates/fuse-parser/tests/cases/pass/function-declaration-02/case.fuse
+---
+[
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 0,
+        end: 8,
+      ),
+      kind: Function,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 8,
+          end: 9,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 9,
+        end: 13,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 13,
+        end: 14,
+      ),
+      kind: LParen,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 14,
+        end: 15,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 15,
+        end: 16,
+      ),
+      kind: Comma,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 16,
+          end: 17,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 17,
+        end: 18,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 18,
+        end: 19,
+      ),
+      kind: Comma,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 19,
+          end: 20,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 20,
+        end: 21,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 21,
+        end: 22,
+      ),
+      kind: Comma,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 22,
+        end: 23,
+      ),
+      kind: RParen,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 23,
+          end: 25,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 25,
+        end: 26,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 26,
+          end: 27,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 27,
+        end: 30,
+      ),
+      kind: End,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 30,
+          end: 31,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+]
diff --git a/crates/fuse-parser/tests/cases/pass/function-declaration-03/ast.snap b/crates/fuse-parser/tests/cases/pass/function-declaration-03/ast.snap
new file mode 100644
index 0000000..4ceff35
--- /dev/null
+++ b/crates/fuse-parser/tests/cases/pass/function-declaration-03/ast.snap
@@ -0,0 +1,62 @@
+---
+source: crates/fuse-parser/tests/cases/mod.rs
+expression: parsed.chunk
+input_file: crates/fuse-parser/tests/cases/pass/function-declaration-03/case.fuse
+---
+Some(Chunk(
+  span: Span(
+    start: 0,
+    end: 16,
+  ),
+  body: Block(
+    statements: [
+      FunctionDeclaration(Function(
+        span: Span(
+          start: 0,
+          end: 15,
+        ),
+        identifier: Some(Identifier(
+          span: Span(
+            start: 3,
+            end: 7,
+          ),
+          name: Atom("test"),
+        )),
+        params: FunctionParameters(
+          span: Span(
+            start: 7,
+            end: 10,
+          ),
+          items: [
+            FunctionParameter(
+              span: Span(
+                start: 8,
+                end: 9,
+              ),
+              pattern: BindingPattern(
+                kind: Identifier(BindingIdentifier(
+                  span: Span(
+                    start: 8,
+                    end: 9,
+                  ),
+                  atom: Atom("a"),
+                )),
+                type_annotation: None,
+                optional: false,
+              ),
+            ),
+          ],
+          rest: None,
+        ),
+        return_type: None,
+        body: Expression(Identifier(Identifier(
+          span: Span(
+            start: 14,
+            end: 15,
+          ),
+          name: Atom("a"),
+        ))),
+      )),
+    ],
+  ),
+))
diff --git a/crates/fuse-parser/tests/cases/pass/function-declaration-03/case.fuse b/crates/fuse-parser/tests/cases/pass/function-declaration-03/case.fuse
new file mode 100644
index 0000000..da49bea
--- /dev/null
+++ b/crates/fuse-parser/tests/cases/pass/function-declaration-03/case.fuse
@@ -0,0 +1 @@
+fn test(a) => a
diff --git a/crates/fuse-parser/tests/cases/pass/function-declaration-03/tokens.snap b/crates/fuse-parser/tests/cases/pass/function-declaration-03/tokens.snap
new file mode 100644
index 0000000..314d888
--- /dev/null
+++ b/crates/fuse-parser/tests/cases/pass/function-declaration-03/tokens.snap
@@ -0,0 +1,116 @@
+---
+source: crates/fuse-parser/tests/cases/mod.rs
+expression: tokens
+input_file: crates/fuse-parser/tests/cases/pass/function-declaration-03/case.fuse
+---
+[
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 0,
+        end: 2,
+      ),
+      kind: Fn,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 2,
+          end: 3,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 3,
+        end: 7,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 7,
+        end: 8,
+      ),
+      kind: LParen,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 8,
+        end: 9,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 9,
+        end: 10,
+      ),
+      kind: RParen,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 10,
+          end: 11,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 11,
+        end: 13,
+      ),
+      kind: Arrow,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 13,
+          end: 14,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+  TokenReference(
+    token: Token(
+      span: Span(
+        start: 14,
+        end: 15,
+      ),
+      kind: Identifier,
+    ),
+    leading_trivia: [],
+    trailing_trivia: [
+      Token(
+        span: Span(
+          start: 15,
+          end: 16,
+        ),
+        kind: Whitespace,
+      ),
+    ],
+  ),
+]