More defined list-to-V/M operators: (|>|), (>|<).

Provides analogs of the (|>) and (><) operators that first apply an
appropriate 'take' to the given lists so that they may be safely used
on lists that are too long (or infinite) -- a feature I find 
particularly useful from the interactive prompt.

As these operators are more defined, I would ask the package maintainer 
to consider, rather than adding (|>|) and (>|<), just updating the
definitions of (|>) and (><) with the new semantics.

3 files changed, 34 insertions, 2 deletions

diff --git a/lib/Data/Packed/Internal/Vector.hs b/lib/Data/Packed/Internal/Vector.hs
index d410c4d..0e6b3f4 100644
--- a/lib/Data/Packed/Internal/Vector.hs
+++ b/lib/Data/Packed/Internal/Vector.hs
@@ -96,6 +96,19 @@ toList v = safeRead v $ peekArray (dim v)
 infixl 9 |>
 n |> l = if length l == n then fromList l else error "|> with wrong size"
 
+{- | Like '(|>)', but explicitly truncates the list, if it is too long.
+
+It may safely be used, for instance, with infinite lists.
+-}
+(|>|) :: (Storable a) => Int -> [a] -> Vector a
+infixl 9 |>|
+n |>| l = if length l' == n then 
+              fromList l' 
+            else 
+              error "|>|: list too short"
+  where l' = take n l
+
+
 -- | access to Vector elements without range checking
 at' :: Storable a => Vector a -> Int -> a
 at' v n = safeRead v $ flip peekElemOff n
diff --git a/lib/Data/Packed/Matrix.hs b/lib/Data/Packed/Matrix.hs
index 4fd61a1..5a73c06 100644
--- a/lib/Data/Packed/Matrix.hs
+++ b/lib/Data/Packed/Matrix.hs
@@ -16,7 +16,7 @@
 module Data.Packed.Matrix (
     Element,
     Matrix,rows,cols,
-    (><),
+    (><), (>|<),
     trans,
     reshape, flatten,
     fromLists, toLists,
@@ -126,6 +126,25 @@ r >< c = f where
                                  ++show (dim v) ++" in ("++show r++"><"++show c++")"
         where v = fromList l
 
+{- | Like '(><)', but explicitly truncates the list, so that it can
+safely be used with lists that are too long (like infinite lists).
+
+Example:
+
+@\> (2>|<3)[1..]
+(2><3)
+ [ 1.0, 2.0, 3.0
+ , 4.0, 5.0, 6.0 ]@
+
+Effectively, a more defined version of '(><)'.
+-}
+(>|<) :: (Element a) => Int -> Int -> [a] -> Matrix a
+r >|< c = f where
+    f l | dim v == r*c = matrixFromVector RowMajor c v
+        | otherwise    = error $ "inconsistent list size = "
+                                 ++show (dim v) ++" in ("++show r++"><"++show c++")"
+        where v = fromList $ take (r*c) l
+
 ----------------------------------------------------------------
 
 -- | Creates a matrix with the first n rows of another matrix
diff --git a/lib/Data/Packed/Vector.hs b/lib/Data/Packed/Vector.hs
index e53d455..ae30c27 100644
--- a/lib/Data/Packed/Vector.hs
+++ b/lib/Data/Packed/Vector.hs
@@ -14,7 +14,7 @@
 
 module Data.Packed.Vector (
     Vector,
-    fromList, (|>), toList,
+    fromList, (|>), (|>|), toList,
     dim, (@>),
     subVector, join,
     constant, linspace,