diff --git a/src/fmt.rs b/src/fmt.rs
new file mode 100644
index 0000000000..4946b0c10e
--- /dev/null
+++ b/src/fmt.rs
@@ -0,0 +1,75 @@
+use parse::ast::CommentOrNewline::Newline;
+use parse::ast::{AssignedField, Expr, Pattern};
+
+pub fn is_multiline_expr<'a>(expr: &'a Expr<'a>) -> bool {
+    use parse::ast::Expr::*;
+    // TODO cache these answers using a Map<Pointer, bool>, so
+    // we don't have to traverse subexpressions repeatedly
+
+    match expr {
+        // Return whether these spaces contain any Newlines
+        SpaceBefore(_, spaces) | SpaceAfter(_, spaces) => {
+            spaces.iter().any(|space| space == &Newline)
+        }
+
+        // These expressions never have newlines
+        Float(_)
+        | Int(_)
+        | HexInt(_)
+        | OctalInt(_)
+        | BinaryInt(_)
+        | Str(_)
+        | Field(_, _)
+        | QualifiedField(_, _)
+        | AccessorFunction(_)
+        | Var(_, _)
+        | MalformedIdent(_)
+        | MalformedClosure
+        | Variant(_, _) => false,
+
+        // These expressions always have newlines
+        Defs(_, _) | Case(_, _) => true,
+
+        List(elems) => elems
+            .iter()
+            .any(|loc_expr| is_multiline_expr(&loc_expr.value)),
+
+        BlockStr(lines) => lines.len() > 1,
+        Apply(loc_expr, args, _) => {
+            is_multiline_expr(&loc_expr.value)
+                || args.iter().any(|loc_arg| is_multiline_expr(&loc_arg.value))
+        }
+
+        If((loc_cond, loc_if_true, loc_if_false)) => {
+            is_multiline_expr(&loc_cond.value)
+                || is_multiline_expr(&loc_if_true.value)
+                || is_multiline_expr(&loc_if_false.value)
+        }
+
+        Operator((loc_left, _, loc_right)) => {
+            is_multiline_expr(&loc_left.value) || is_multiline_expr(&loc_right.value)
+        }
+
+        PrecedenceConflict(_, _, loc_expr) => is_multiline_expr(&loc_expr.value),
+
+        Closure(loc_patterns, loc_body) => {
+            // check the body first because it's more likely to be multiline
+            is_multiline_expr(&loc_body.value)
+                || loc_patterns
+                    .iter()
+                    .any(|loc_pattern| is_multiline_pattern(&loc_pattern.value))
+        }
+
+        Record(loc_fields) => loc_fields
+            .iter()
+            .any(|loc_field| is_multiline_field(&loc_field.value)),
+    }
+}
+
+pub fn is_multiline_field<'a, Val>(_field: &'a AssignedField<'a, Val>) -> bool {
+    panic!("TODO return iff there are any newlines")
+}
+
+pub fn is_multiline_pattern<'a>(_pattern: &'a Pattern<'a>) -> bool {
+    panic!("TODO return iff there are any newlines")
+}
diff --git a/src/lib.rs b/src/lib.rs
index fbdef85776..60e3527b6c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,6 +12,7 @@ pub mod string;
 
 pub mod constrain;
 pub mod ena;
+pub mod fmt;
 pub mod infer;
 pub mod pretty_print_types;
 pub mod solve;