cleanup

1 files changed, 0 insertions, 176 deletions

diff --git a/gemfeed/.rcmbackup/2010-04-09-standard-ml-and-haskell.gmi.tpl.94827a5494a2149e0e0f68d54010656f2fc707f8265377a801426e1e04351f3b b/gemfeed/.rcmbackup/2010-04-09-standard-ml-and-haskell.gmi.tpl.94827a5494a2149e0e0f68d54010656f2fc707f8265377a801426e1e04351f3b
deleted file mode 100644
index a3d3ed79..00000000
--- a/gemfeed/.rcmbackup/2010-04-09-standard-ml-and-haskell.gmi.tpl.94827a5494a2149e0e0f68d54010656f2fc707f8265377a801426e1e04351f3b
+++ /dev/null
@@ -1,176 +0,0 @@
-# Standard ML and Haskell
-
-> Published at 2010-04-09T22:57:36+01:00
-
-I am currently looking into the functional programming language Standard ML (aka SML). The purpose is to refresh my functional programming skills and to learn something new too. Since I already knew a little Haskell, I could not help myself, and I also implemented the same exercises in Haskell.
-
-As you will see, SML and Haskell are very similar (at least when it comes to the basics). However, the syntax of Haskell is a bit more "advanced". Haskell utilizes fewer keywords (e.g. no val, end, fun, fn ...). Haskell also allows to write down the function types explicitly. What I have been missing in SML so far is the so-called pattern guards. Although this is a very superficial comparison for now, so far, I like Haskell more than SML. Nevertheless, I thought it would be fun to demonstrate a few simple functions of both languages to show off the similarities. 
-
-Haskell is also a "pure functional" programming language, whereas SML also makes explicit use of imperative concepts. I am by far not a specialist in either of these languages, but here are a few functions implemented in both SML and Haskell:
-
-<< template::inline::toc
-
-## Defining a multi-data type
-
-Standard ML:
-
-```sml
-datatype ’a multi
-	= EMPTY
-	| ELEM of ’a
-	| UNION of ’a multi * ’a multi
-```
-
-Haskell:
-
-```haskell
-data (Eq a) => Multi a
-    = Empty
-    | Elem a
-    | Union (Multi a) (Multi a)
-    deriving Show
-```
-
-## Processing a multi
-
-Standard ML:
-
-```sml
-fun number (EMPTY) _ = 0
-	| number (ELEM x) w = if x = w then 1 else 0
-	| number (UNION (x,y)) w = (number x w) + (number y w)
-fun test_number w = number (UNION (EMPTY, \
-    UNION (ELEM 4, UNION (ELEM 6, \
-    UNION (UNION (ELEM 4, ELEM 4), EMPTY))))) w 
-```
-
-Haskell:
-
-```haskell
-number Empty _ = 0
-number (Elem x) w = if x == w then 1 else 0
-test_number w = number (Union Empty \
-    (Union (Elem 4) (Union (Elem 6) \
-    (Union (Union (Elem 4) (Elem 4)) Empty)))) w
-```
-
-## Simplify function
-
-Standard ML:
-
-```sml
-fun simplify (UNION (x,y)) =
-    let fun is_empty (EMPTY) = true | is_empty _ = false
-        val x’ = simplify x
-        val y’ = simplify y
-    in if (is_empty x’) andalso (is_empty y’)
-            then EMPTY
-       else if (is_empty x’)
-            then y’
-       else if (is_empty y’)
-            then x’
-       else UNION (x’, y’)
-    end
-  | simplify x = x
-```
-
-Haskell:
-
-```haskell
-simplify (Union x y)
-    | (isEmpty x’) && (isEmpty y’) = Empty
-    | isEmpty x’ = y’
-    | isEmpty y’ = x’
-    | otherwise = Union x’ y’
-    where
-        isEmpty Empty = True
-        isEmpty _ = False
-        x’ = simplify x
-        y’ = simplify y
-simplify x = x
-```
-
-## Delete all
-
-Standard ML:
-
-```sml
-fun delete_all m w =
-    let fun delete_all’ (ELEM x) = if x = w then EMPTY else ELEM x
-          | delete_all’ (UNION (x,y)) = UNION (delete_all’ x, delete_all’ y)
-          | delete_all’ x = x
-    in simplify (delete_all’ m)
-    end
-```
-
-Haskell:
-
-```haskell
-delete_all m w = simplify (delete_all’ m)
-    where
-        delete_all’ (Elem x) = if x == w then Empty else Elem x
-        delete_all’ (Union x y) = Union (delete_all’ x) (delete_all’ y)
-        delete_all’ x = x
-```
-
-## Delete one
-
-Standard ML:
-
-```sml
-fun delete_one m w =
-    let fun delete_one’ (UNION (x,y)) =
-            let val (x’, deleted) = delete_one’ x
-                in if deleted
-                   then (UNION (x’, y), deleted)
-                   else let val (y’, deleted) = delete_one’ y
-                       in (UNION (x, y’), deleted)
-                   end
-                end
-          | delete_one’ (ELEM x) =
-            if x = w then (EMPTY, true) else (ELEM x, false)
-          | delete_one’ x = (x, false)
-            val (m’, _) = delete_one’ m
-        in simplify m’
-    end
-```
-
-Haskell:
-
-```haskell
-delete_one m w = do
-    let (m’, _) = delete_one’ m
-    simplify m’
-    where
-        delete_one’ (Union x y) =
-            let (x’, deleted) = delete_one’ x
-            in if deleted
-                then (Union x’ y, deleted)
-                else let (y’, deleted) = delete_one’ y
-                    in (Union x y’, deleted)
-        delete_one’ (Elem x) =
-            if x == w then (Empty, True) else (Elem x, False)
-        delete_one’ x = (x, False)
-```
-
-## Higher-order functions
-
-The first line is always the SML code, the second line the Haskell variant:
-
-```
-fun make_map_fn f1 = fn (x,y) => f1 x :: y
-make_map_fn f1 = \x y -> f1 x : y
-
-fun make_filter_fn f1 = fn (x,y) => if f1 x then x :: y else y
-make_filter_fn f1 = \x y -> if f1 then x : y else y
-
-fun my_map f l = foldr (make_map_fn f) [] l
-my_map f l = foldr (make_map_fn f) [] l
-
-fun my_filter f l = foldr (make_filter_fn f) [] l
-my_filter f l = foldr (make_filter_fn f) [] l
-```
-
-E-Mail your comments to `paul@nospam.buetow.org` :-)
-
-=> ../ Back to the main site