progress functorising text builder

fcore/make-text-builder.sml

@@ -0,0 +1,31 @@
+signature MAKE_TEXT_BUILDER =
+sig
+  type state
+  type env
+
+  type pos_data =
+    {chr: char, strIdx: int, absIdx: int, hd: string, tl: string list}
+
+  val folder: pos_data * env * state -> state
+  val stopFold: state -> bool
+end
+
+functor MakeTextBuilder(Fn: MAKE_TEXT_BUILDER) =
+struct
+  fun buildLoop (strIdx, absIdx, hd, tl, env, state) =
+    if Fn.stopFold state then
+      state
+    else if strIdx = String.size hd then
+      case tl of
+        hd :: tl => buildLoop (0, absIdx, hd, tl, env, state)
+      | [] => state
+    else
+      let
+        val chr = String.sub (hd, strIdx)
+        val posData =
+          {chr = chr, strIdx = strIdx, absIdx = absIdx, hd = hd, tl = tl}
+        val state = Fn.folder (posData, env, state)
+      in
+        buildLoop (strIdx + 1, absIdx + 1, hd, tl, env, state)
+      end
+end