Merge pull request #536 from MatthewFluet/imperativeio-getinstream-bug

Fix bug in `ImperativeIO(...).getInstream`

Author: MatthewFluet

basis-library/io/imperative-io.fun

@@ -1,4 +1,4 @@
-(* Copyright (C) 2013,2017 Matthew Fluet.
+(* Copyright (C) 2013,2017,2023 Matthew Fluet.
  * Copyright (C) 2002-2007 Henry Cejtin, Matthew Fluet, Suresh
  *    Jagannathan, and Stephen Weeks.
  *
@@ -681,7 +681,7 @@ fun getInstream (ib as In {state, ...}) =
                                        AS.vector (AS.slice (buf, f, 
                                                             SOME (l - f)))))
                         else doit (false, NONE)
-                  val () = state := Stream s
+                  val () = setInstream (ib, s)
                in
                   s
                end

regression/textio.3.ok

@@ -0,0 +1,43 @@
+(* See https://github.com/MLton/mlton/issues/535. *)
+
+datatype tree = Leaf of char | Node of tree * tree
+
+fun nextis c cs =
+  case TextIO.StreamIO.input1 (TextIO.getInstream cs) of
+    NONE => false
+  | SOME (c', cs') => c' = c
+
+(* This version works. *)
+(*
+fun nextis c cs =
+  case TextIO.lookahead cs of
+    NONE => false
+  | SOME c' => c' = c
+*)
+
+fun discard c cs =
+  let val c' = valOf (TextIO.input1 cs) in
+    if c = c'
+    then ()
+    else raise Fail ("unexpected character: " ^ Char.toString c' ^ ", expecting: " ^ Char.toString c)
+  end
+
+fun parse cs =
+  case valOf (TextIO.input1 cs) of
+   #"(" =>
+      let
+        fun loop l r =
+          if nextis #")" cs
+          then (discard #")" cs; Node (l, r))
+          else loop (Node (l, r)) (parse cs)
+      in
+        loop (parse cs) (parse cs)
+      end
+  | c => Leaf c
+
+val cs = TextIO.openString "(a(bc)d)"
+
+(* with this it works too *)
+(* val true = nextis #"(" cs *)
+
+val t = (parse cs)