Add seek() operation with tests. (#25)

* Add seek() operation with tests.

* Workaround for Nim issue with `|`.

* Range length from int32 to int.
seek() got renamed to advance().
Zero advance is allowed.
tryAdvance() is now non-throw version of advance().

* Allow advance() to make zero length ranges.

ranges/typedranges.nim

@@ -9,7 +9,7 @@ type
     when rangesGCHoldEnabled:
       gcHold: seq[T]
     start: ptr T
-    mLen: int32
+    mLen: int
 
   # A view into mutable array
   MutRange*[T] = distinct Range[T]
@@ -22,13 +22,13 @@ proc toImmutableRange[T](a: seq[T]): Range[T] =
     when rangesGCHoldEnabled:
       result.gcHold = a
     result.start = addr result.gcHold[0]
-    result.mLen = int32(a.len)
+    result.mLen = a.len
 
 when unsafeAPIEnabled:
   proc toImmutableRangeNoGCHold[T](a: openarray[T]): Range[T] =
     if a.len != 0:
       result.start = unsafeAddr a[0]
-      result.mLen = int32(a.len)
+      result.mLen = a.len
 
   proc toImmutableRange[T](a: openarray[T]): Range[T] {.inline.} =
     toImmutableRangeNoGCHold(a)
@@ -122,7 +122,7 @@ proc sliceNormalized[T](r: Range[T], ibegin, iend: int): Range[T] =
   when rangesGCHoldEnabled:
     result.gcHold = r.gcHold
   result.start = r.start.shift(ibegin)
-  result.mLen = int32(iend - ibegin + 1)
+  result.mLen = iend - ibegin + 1
 
 proc slice*[T](r: Range[T], ibegin = 0, iend = -1): Range[T] =
   let e = if iend < 0: r.len + iend
@@ -192,3 +192,43 @@ proc `&`*[T](a, b: Range[T]): seq[T] =
 
 proc hash*(x: Range): Hash =
   result = hash(toOpenArray(x))
+
+template advanceImpl(a, b: untyped): bool =
+  var res = false
+  if b == 0:
+    res = true
+  elif b > 0:
+    if isNil(a.start) or a.mLen <= 0:
+      res = false
+    else:
+      if a.mLen - b < 0:
+        res = false
+      else:
+        a.start = a.start.shift(b)
+        a.mLen -= b
+        res = true
+  res
+
+proc tryAdvance*[T](x: var Range[T], idx: int): bool =
+  ## Move internal start offset of range ``x`` by ``idx`` elements forward.
+  ## 
+  ## Returns ``true`` if operation got completed successfully, or
+  ## ``false`` if you are trying to overrun range ``x``. 
+  result = x.advanceImpl(idx)
+
+proc tryAdvance*[T](x: var MutRange[T], idx: int): bool =
+  ## Move internal start offset of range ``x`` by ``idx`` elements forward.
+  ## 
+  ## Returns ``true`` if operation got completed successfully, or
+  ## ``false`` if you are trying to overrun range ``x``. 
+  result = x.advanceImpl(idx)
+
+proc advance*[T](x: var Range[T], idx: int) =
+  ## Move internal start offset of range ``x`` by ``idx`` elements forward.
+  let res = x.advanceImpl(idx)
+  if not res: raise newException(IndexError, "Advance Error")
+
+proc advance*[T](x: var MutRange[T], idx: int) =
+  ## Move internal start offset of range ``x`` by ``idx`` elements forward.
+  let res = x.advanceImpl(idx)
+  if not res: raise newException(IndexError, "Advance Error")

tests/ttypedranges.nim

@@ -102,3 +102,54 @@ suite "Typed ranges":
   test "toOpenArray":
     var a = toRange(@[1,2,3])
     check $a.toOpenArray == "[1, 2, 3]"
+
+  test "tryAdvance":
+    var a: Range[int]
+    check:
+      a.tryAdvance(1) == false
+      a.tryAdvance(-1) == false
+      a.tryAdvance(0) == true
+    var b = toRange(@[1, 2, 3])
+    check:
+      b.tryAdvance(-1) == false
+      $b.toOpenArray == "[1, 2, 3]"
+      b.tryAdvance(0) == true
+      $b.toOpenArray == "[1, 2, 3]"
+      b.tryAdvance(1) == true
+      $b.toOpenArray == "[2, 3]"
+      b.tryAdvance(1) == true
+      $b.toOpenArray == "[3]"
+      b.tryAdvance(1) == true
+      $b.toOpenArray == "[]"
+      b.tryAdvance(1) == false
+      $b.toOpenArray == "[]"
+
+  test "advance":
+    template aecheck(a, b): int =
+      var res = 0
+      try:
+        a.advance(b)
+        res = 1
+      except IndexError:
+        res = 2
+      res
+
+    var a: Range[int]
+    check:
+      a.aecheck(1) == 2
+      a.aecheck(-1) == 2
+      a.aecheck(0) == 1
+    var b = toRange(@[1, 2, 3])
+    check:
+      b.aecheck(-1) == 2
+      $b.toOpenArray == "[1, 2, 3]"
+      b.aecheck(0) == 1
+      $b.toOpenArray == "[1, 2, 3]"
+      b.aecheck(1) == 1
+      $b.toOpenArray == "[2, 3]"
+      b.aecheck(1) == 1
+      $b.toOpenArray == "[3]"
+      b.aecheck(1) == 1
+      $b.toOpenArray == "[]"
+      b.aecheck(1) == 2
+      $b.toOpenArray == "[]"