diff --git a/README.md b/README.md
index 15371da..05521e6 100644
--- a/README.md
+++ b/README.md
@@ -21,8 +21,15 @@ using @cirru_parser {type Cirru}
 // parse Cirru code
 Cirru::parse(code: String) : Array[Cirru] raise CirruParseError
 
+// parse a one-line Cirru expression
+Cirru::parse_expr_one_liner(code: String) : Cirru raise CirruParseError
+
 // format Cirru code
 Cirru::format(cirru: Array[Cirru], use_inline=false) : String raise FormatCirruError
+
+// format one expression into one line
+Cirru::format_expr_one_liner(expr: Cirru) : String raise FormatCirruError
+Cirru::format_one_liner(expr: Cirru) : String raise FormatCirruError
 ```
 
 ### License
diff --git a/src/parser.mbt b/src/parser.mbt
index 0f8f995..015ee57 100644
--- a/src/parser.mbt
+++ b/src/parser.mbt
@@ -13,7 +13,7 @@ fn build_exprs(
     idx += 1
     Some(tokens[pos])
   }
-  for {
+  for ;; {
     let chunk = pull_token()
     match chunk {
       None => return acc
@@ -23,7 +23,7 @@ fn build_exprs(
             let mut pointer : Array[Cirru] = Array::new(capacity=8)
             // guess a nested level of 16
             let pointer_stack : Array[Array[Cirru]] = Array::new(capacity=16)
-            for {
+            for ;; {
               let cursor = pull_token()
               match cursor {
                 None => raise CirruParseError("unexpected end of file")
@@ -68,6 +68,18 @@ pub fn Cirru::parse(code : String) -> Array[Cirru] raise CirruParseError {
   resolve_comma(resolve_dollar(tree))
 }
 
+///|
+/// parse a one-line Cirru expression into exactly one expression
+pub fn Cirru::parse_expr_one_liner(
+  code : String,
+) -> Cirru raise CirruParseError {
+  let xs = Cirru::parse(code)
+  if xs.length() != 1 {
+    raise CirruParseError("expected 1 expression, got \{xs.length()}")
+  }
+  xs[0]
+}
+
 ///|
 suberror CirruParseError {
   CirruParseError(String)
@@ -280,7 +292,7 @@ fn resolve_indentations(tokens : Array[CirruLexItem]) -> Array[CirruLexItem] {
   let mut acc : Array[CirruLexItem] = Array::new()
   let mut level = 0
   let mut pointer = 0
-  for {
+  for ;; {
     if pointer >= size {
       if acc.is_empty() {
         return Array::new()
diff --git a/src/parser_test.mbt b/src/parser_test.mbt
index 3946a9c..15b651b 100644
--- a/src/parser_test.mbt
+++ b/src/parser_test.mbt
@@ -3,7 +3,91 @@ using @lib {type Cirru}
 
 ///|
 test "parser" {
-  assert_eq(Cirru::parse("def a"), [List([Leaf("def"), Leaf("a")])])
+  assert_eq(Cirru::parse("def a"), [
+    Cirru::List([Cirru::Leaf("def"), Cirru::Leaf("a")]),
+  ])
+}
+
+///|
+test "parse and format one-liner expression" {
+  let tree = Cirru::List([
+    Cirru::Leaf("defn"),
+    Cirru::Leaf("main"),
+    Cirru::List([]),
+    Cirru::List([Cirru::Leaf("println"), Cirru::Leaf("Hello, world!")]),
+  ])
+
+  let one_liner = try! tree.format_one_liner()
+  assert_eq(one_liner, "defn main () $ println \"Hello, world!\"")
+
+  let parsed = try! Cirru::parse_expr_one_liner(one_liner)
+  assert_eq(parsed, tree)
+}
+
+///|
+test "reject multiple expressions in one-liner parser" {
+  let result = try? Cirru::parse_expr_one_liner("a\nb")
+  match result {
+    Err(err) => assert_eq(err.to_string(), "expected 1 expression, got 2")
+    Ok(_) => assert_eq("ok", "err")
+  }
+}
+
+///|
+test "format complex one-liner expression" {
+  let tree = Cirru::List([
+    Cirru::Leaf("a"),
+    Cirru::List([Cirru::Leaf("b"), Cirru::List([Cirru::Leaf("c")])]),
+    Cirru::Leaf("d"),
+  ])
+
+  let one_liner = try! tree.format_one_liner()
+  assert_eq(one_liner, "a (b (c)) d")
+
+  let parsed = try! Cirru::parse_expr_one_liner(one_liner)
+  assert_eq(parsed, tree)
+}
+
+///|
+test "format tail expression one-liner" {
+  let tree = Cirru::List([
+    Cirru::Leaf("defn"),
+    Cirru::Leaf("main"),
+    Cirru::List([]),
+    Cirru::List([Cirru::Leaf("println"), Cirru::Leaf("Hello")]),
+  ])
+
+  let one_liner = try! tree.format_one_liner()
+  assert_eq(one_liner, "defn main () $ println Hello")
+
+  let parsed = try! Cirru::parse_expr_one_liner(one_liner)
+  assert_eq(parsed, tree)
+}
+
+///|
+test "format nested tail expression one-liner" {
+  let tree = Cirru::List([
+    Cirru::Leaf("if"),
+    Cirru::Leaf("condition"),
+    Cirru::List([Cirru::Leaf("do"), Cirru::List([Cirru::Leaf("action")])]),
+  ])
+
+  let one_liner = try! tree.format_one_liner()
+  assert_eq(one_liner, "if condition $ do $ action")
+
+  let parsed = try! Cirru::parse_expr_one_liner(one_liner)
+  assert_eq(parsed, tree)
+}
+
+///|
+test "format empty tail expression one-liner" {
+  let tree = Cirru::List([Cirru::Leaf("a"), Cirru::Leaf("b"), Cirru::List([])])
+
+  let one_liner = try! tree.format_one_liner()
+  assert_eq(one_liner, "a b $")
+
+  let parsed = try! Cirru::parse_expr_one_liner(one_liner)
+  assert_eq(parsed, tree)
 }
 
 ///|
diff --git a/src/primes.mbt b/src/primes.mbt
index ba67bca..7a0cd3c 100644
--- a/src/primes.mbt
+++ b/src/primes.mbt
@@ -149,6 +149,12 @@ pub fn Cirru::is_comment(self : Cirru) -> Bool {
   }
 }
 
+///|
+/// format this expression into a single line of Cirru code
+pub fn Cirru::format_one_liner(self : Cirru) -> String raise FormatCirruError {
+  Cirru::format_expr_one_liner(self)
+}
+
 ///|
 /// lexer is a simpler state machine to tokenize Cirru code
 priv enum CirruLexState {
diff --git a/src/s_expr.mbt b/src/s_expr.mbt
index 15eb5c3..45d3e88 100644
--- a/src/s_expr.mbt
+++ b/src/s_expr.mbt
@@ -46,7 +46,7 @@ fn Cirru::format_lispy_expr(
             chunk = "\{chunk}\{next}"
           }
           // TODO dirty way, but intuitive for now
-          if idx < xs.length() - 1 && not(ends_with_newline(chunk)) {
+          if idx < xs.length() - 1 && !ends_with_newline(chunk) {
             chunk = "\{chunk} "
           }
         }
@@ -58,7 +58,7 @@ fn Cirru::format_lispy_expr(
       } else {
         let s0 = token[0]
         if s0 == '|' || s0 == '"' {
-          let sliced = (try! token[1:]).to_string()
+          let sliced = token[1:].to_owned()
           "\"" + escape_string(sliced) + "\""
         } else if token.contains(" ") ||
           token.contains("\n") ||
diff --git a/src/tree.mbt b/src/tree.mbt
index 261c484..bb77ea1 100644
--- a/src/tree.mbt
+++ b/src/tree.mbt
@@ -12,18 +12,18 @@ fn comma_helper(initial_after : Array[Cirru]) -> Array[Cirru] {
   let before : Array[Cirru] = Array::new(capacity=initial_after.length())
   let after : Array[Cirru] = initial_after
   let mut pointer = 0
-  for {
+  for ;; {
     if pointer >= after.length() {
       return before
     }
     match after[pointer] {
       List(xs) =>
-        if not(xs.is_empty()) {
+        if !xs.is_empty() {
           match xs[0] {
             List(_) => before.push(List(resolve_comma(xs)))
             Leaf(s) =>
               if s == "," {
-                before.push_iter(resolve_comma(xs[1:].to_array()).iter())
+                before.push_iter(resolve_comma(xs[1:].to_owned()).iter())
               } else {
                 before.push(List(resolve_comma(xs)))
               }
@@ -51,7 +51,7 @@ fn dollar_helper(initial_after : Array[Cirru]) -> Array[Cirru] {
   let before : Array[Cirru] = Array::new(capacity=initial_after.length())
   let after : Array[Cirru] = initial_after
   let mut pointer = 0
-  for {
+  for ;; {
     if pointer >= after.length() {
       return before
     } else {
diff --git a/src/writer.mbt b/src/writer.mbt
index 5cad15c..547864b 100644
--- a/src/writer.mbt
+++ b/src/writer.mbt
@@ -83,7 +83,7 @@ fn is_char_allowed(x : Char) -> Bool {
 fn generate_leaf(s : String) -> String {
   let mut all_allowed = true
   for x in s {
-    if not(is_char_allowed(x)) {
+    if !is_char_allowed(x) {
       all_allowed = false
       break
     }
@@ -131,6 +131,33 @@ fn generate_inline_expr(xs : Array[Cirru]) -> String {
   result
 }
 
+///|
+fn generate_statement_one_liner(xs : Array[Cirru]) -> String {
+  let mut ret = ""
+  let size = xs.length()
+  for idx, cursor in xs {
+    if idx > 0 {
+      ret += " "
+    }
+    let at_tail = idx > 0 && idx == size - 1
+    match cursor {
+      Leaf(s) => ret += generate_leaf(s)
+      List(ys) =>
+        if at_tail {
+          if ys.is_empty() {
+            ret += "$"
+          } else {
+            ret += "$ "
+            ret += generate_statement_one_liner(ys)
+          }
+        } else {
+          ret += generate_inline_expr(ys)
+        }
+    }
+  }
+  ret
+}
+
 ///|
 /// by 2 spaces
 fn push_spaces(buf : String, n : Int) -> String {
@@ -170,7 +197,7 @@ fn Cirru::get_node_kind(self : Cirru) -> WriterNode {
 ///|
 pub(all) suberror FormatCirruError {
   FormatCirruError(String)
-} derive(Show)
+} derive(Debug)
 
 ///|
 fn generate_tree(
@@ -188,7 +215,7 @@ fn generate_tree(
     let next_level = level + 1
     let child_insist_head = prev_kind == BoxedExpr || prev_kind == Expr
     let at_tail = idx != 0 &&
-      not(in_tail) &&
+      !in_tail &&
       prev_kind == Leaf &&
       idx == xs.length() - 1
 
@@ -343,3 +370,15 @@ pub fn Cirru::format(
 ) -> String raise FormatCirruError {
   generate_statements(xs, use_inline~)
 }
+
+///|
+/// format a single Cirru expression as a single line
+pub fn Cirru::format_expr_one_liner(
+  expr : Cirru,
+) -> String raise FormatCirruError {
+  match expr {
+    Leaf(_) =>
+      raise FormatCirruError("format_expr_one_liner expects an expr (list)")
+    List(xs) => generate_statement_one_liner(xs)
+  }
+}