diff --git a/impls/sml/core.sml b/impls/sml/core.sml
index 79ee4b96..d937a57b 100644
--- a/impls/sml/core.sml
+++ b/impls/sml/core.sml
@@ -118,7 +118,13 @@ val coreIo = [
     FN (fn args => args |> map prReadableStr |> String.concatWith " " |> malPrint),
 
     SYMBOL "println",
-    FN (fn args => args |> map prStr         |> String.concatWith " " |> malPrint)
+    FN (fn args => args |> map prStr         |> String.concatWith " " |> malPrint),
+
+    SYMBOL "readline",
+    FN (fn [STRING prompt] => (TextIO.print prompt;
+                               valOrElse (TextIO.inputLine TextIO.stdIn |> Option.map (STRING o (trimr 1)))
+                                         (fn () => NIL))
+         | _ => raise NotApplicable "readline requires a string")
 ]
 
 fun arithFolder n f (INT next, INT prev) = INT (f (prev, next))
diff --git a/impls/sml/util.sml b/impls/sml/util.sml
index 629e1015..b410fe07 100644
--- a/impls/sml/util.sml
+++ b/impls/sml/util.sml
@@ -26,6 +26,8 @@ fun identity x = x
 
 fun triml k s = String.extract (s, k, NONE)
 
+fun trimr k s = String.substring (s, 0, String.size s - k)
+
 fun malEscape s = String.translate (fn #"\"" => "\\\""
                                      | #"\n" => "\\n"
                                      | #"\\" => "\\\\"