diff --git a/fcore/app-with.sml b/fcore/app-with.sml
index 1412380..3c691e7 100644
--- a/fcore/app-with.sml
+++ b/fcore/app-with.sml
@@ -10,7 +10,7 @@ struct
         , buffer
         , bufferModifyTime
         , searchList
-        , searchString
+        , dfa
         , mode
         , windowWidth
         , windowHeight
@@ -23,7 +23,7 @@ struct
       , buffer = buffer
       , bufferModifyTime = bufferModifyTime
       , searchList = searchList
-      , searchString = searchString
+      , dfa = dfa
       , mode = mode
       , windowWidth = windowWidth
       , windowHeight = windowHeight
diff --git a/fcore/search-list/dfa-gen.sml b/fcore/search-list/dfa-gen.sml
index 47838f2..6686bb7 100644
--- a/fcore/search-list/dfa-gen.sml
+++ b/fcore/search-list/dfa-gen.sml
@@ -15,6 +15,8 @@ sig
   val nextState: dfa * dfa_state * char -> dfa_state
   val isFinal: dfa * dfa_state -> bool
   val isDead: dfa_state -> bool
+
+  val matchString: dfa * string -> (int * int) list
 end
 
 functor MakeDfaGen(Fn: DFA_GEN_PARAMS): DFA_GEN =
@@ -817,6 +819,41 @@ struct
     end
 
   fun isDead (curState: dfa_state) = curState = ~1
+
+  fun helpMatchString (strPos, str, dfa, curState, startPos, prevFinalPos, acc) =
+    if strPos = String.size str then
+      let
+        val acc =
+          if prevFinalPos = ~1 then acc else (startPos, prevFinalPos) :: acc
+      in
+        List.rev acc
+      end
+    else
+      let
+        val chr = String.sub (str, strPos)
+        val newState = nextState (dfa, curState, chr)
+        val prevFinalPos =
+          if isFinal (dfa, newState) then strPos else prevFinalPos
+      in
+        if isDead newState then
+          if prevFinalPos = ~1 then
+            (* restart from startPos *)
+            helpMatchString (startPos + 1, str, dfa, 0, startPos + 1, ~1, acc)
+          else
+            let
+              val acc = (startPos, prevFinalPos) :: acc
+            in
+              helpMatchString
+                (prevFinalPos + 1, str, dfa, 0, prevFinalPos + 1, ~1, acc)
+            end
+        else
+          helpMatchString
+            (strPos + 1, str, dfa, newState, startPos, prevFinalPos, acc)
+      end
+
+  fun matchString (dfa, string) =
+    if Vector.length dfa = 0 then []
+    else helpMatchString (0, string, dfa, 0, 0, ~1, [])
 end
 
 structure CaseInsensitiveDfa =
diff --git a/shf-tests.mlb b/shf-tests.mlb
index 242d8fe..174a748 100644
--- a/shf-tests.mlb
+++ b/shf-tests.mlb
@@ -67,6 +67,7 @@ $(SML_LIB)/basis/mlton.mlb
 shell/exception-logger.sml
 test/Railroad/src/railroad.mlb
 
+test/regex-tests.sml
 test/test-utils.sml
 test/normal-move.sml
 test/normal-delete.sml
diff --git a/test/regex-tests.sml b/test/regex-tests.sml
new file mode 100644
index 0000000..17d02d5
--- /dev/null
+++ b/test/regex-tests.sml
@@ -0,0 +1,43 @@
+structure RegexTests =
+struct
+  open Railroad
+  open Railroad.Test
+
+  structure CiDfa = CaseInsensitiveDfa
+  structure CsDfa = CaseSensitiveDfa
+
+  val caseInsensitiveTests = describe "case insensitive regex"
+    [ test "recognises word 'hello' in string 'Hello world'" (fn _ =>
+        let
+          (* arrange *)
+          val regexString = "hello"
+          val dfa = CiDfa.fromString regexString
+          val inputString = "Hello world"
+
+          (* act *)
+          val matches = CiDfa.matchString (dfa, inputString)
+
+          (* assert *)
+          val expectedMatches = [(0, 4)]
+        in
+          Expect.isTrue (matches = expectedMatches)
+        end)
+    , test "recognises word 'world' in string 'HELLO WORLD'" (fn _ =>
+        let
+          (* arrange *)
+          val regexString = "world"
+          val dfa = CiDfa.fromString regexString
+          val inputString = "HELLO WORLD"
+
+          (* act *)
+          val matches = CiDfa.matchString (dfa, inputString)
+
+          (* assert *)
+          val expectedMatches = [(6, 10)]
+        in
+          Expect.isTrue (matches = expectedMatches)
+        end)
+    ]
+
+  val tests = [caseInsensitiveTests]
+end
diff --git a/test/test.sml b/test/test.sml
index e515900..416569a 100644
--- a/test/test.sml
+++ b/test/test.sml
@@ -6,7 +6,12 @@ struct
   fun main () =
     let
       val tests =
-        List.concat [NormalMove.tests, NormalDelete.tests, Regression.tests]
+        List.concat
+          [ NormalMove.tests
+          , NormalDelete.tests
+          , Regression.tests
+          , RegexTests.tests
+          ]
       val tests = concat tests
     in
       runWithConfig [Configuration.PrintPassed false] tests