fixes #6989

tests/array/troofregression2.nim

@@ -0,0 +1,104 @@
+discard """
+  output: '''OK
+OK
+OK
+OK
+OK
+dflfdjkl__abcdefgasfsgdfgsgdfggsdfasdfsafewfkljdsfajs
+dflfdjkl__abcdefgasfsgdfgsgdfggsdfasdfsafewfkljdsfajsdf
+kgdchlfniambejop
+fjpmholcibdgeakn
+'''
+"""
+
+import strutils, sequtils
+# bug #6989
+
+import typetraits
+
+type Dist = distinct int
+
+proc mypred[T: Ordinal](x: T): T = T(int(x)-1)
+proc cons(x: int): Dist = Dist(x)
+
+var d: Dist
+
+template `^+`(s, i: untyped): untyped =
+  (when i is BackwardsIndex: s.len - int(i) else: int(i))
+
+proc `...`*[T, U](a: T, b: U): HSlice[T, U] =
+  result.a = a
+  result.b = b
+
+proc `...`*[T](b: T): HSlice[int, T] =
+  result.b = b
+
+template `...<`*(a, b: untyped): untyped =
+  ## a shortcut for 'a..pred(b)'.
+  a ... pred(b)
+
+template check(a, b) =
+  if $a == b: echo "OK"
+  else: echo "Failure ", a, " != ", b
+
+check type(4 ...< 1), "HSlice[system.int, system.int]"
+
+check type(4 ...< ^1), "HSlice[system.int, system.BackwardsIndex]"
+check type(4 ... pred(^1)), "HSlice[system.int, system.BackwardsIndex]"
+
+check type(4 ... mypred(8)), "HSlice[system.int, system.int]"
+
+check type(4 ... mypred(^1)), "HSlice[system.int, system.BackwardsIndex]"
+
+var rot = 8
+
+proc bug(s: string): string =
+  result = s
+  result = result[result.len - rot .. ^1] & "__" & result[0 ..< ^rot]
+
+const testStr = "abcdefgasfsgdfgsgdfggsdfasdfsafewfkljdsfajsdflfdjkl"
+
+echo bug(testStr)
+echo testStr[testStr.len - 8 .. testStr.len - 1] & "__" & testStr[0 .. testStr.len - pred(rot)]
+
+
+
+const
+  instructions = readFile("./inputs/16.txt").split(',')
+  programs = "abcdefghijklmnop"
+
+proc dance(dancers: string): string =
+  result = dancers
+  for instr in instructions:
+    let rem = instr[1 .. instr.high]
+    case instr[0]
+    of 's':
+      let rot = rem.parseInt
+      result = result[result.len - rot .. ^1] & result[0 ..< ^rot]
+    of 'x':
+      let
+        x = rem.split('/')
+        a = x[0].parseInt
+        b = x[1].parseInt
+      swap(result[a], result[b])
+    of 'p':
+      let
+        a = result.find(rem[0])
+        b = result.find(rem[^1])
+      result[a] = rem[^1]
+      result[b] = rem[0]
+    else: discard
+
+proc longDance(dancers: string, iterations = 1_000_000_000): string =
+  var
+    dancers = dancers
+    seen = @[dancers]
+  for i in 1 .. iterations:
+    dancers = dancers.dance()
+    if dancers in seen:
+      return seen[iterations mod i]
+    seen.add(dancers)
+
+
+echo dance(programs)
+echo longDance(programs)