diff options
Diffstat (limited to 'src/clojure/contrib/monads/examples.clj')
| -rw-r--r-- | src/clojure/contrib/monads/examples.clj | 50 |
1 files changed, 25 insertions, 25 deletions
diff --git a/src/clojure/contrib/monads/examples.clj b/src/clojure/contrib/monads/examples.clj index 54748d74..7c11fbc2 100644 --- a/src/clojure/contrib/monads/examples.clj +++ b/src/clojure/contrib/monads/examples.clj @@ -25,19 +25,19 @@ ; Monad comprehensions in the sequence monad work exactly the same ; as Clojure's 'for' construct, except that :while clauses are not ; available. -(domonad sequence +(domonad sequence-m [x (range 5) y (range 3)] (+ x y)) ; Inside a with-monad block, domonad is used without the monad name. -(with-monad sequence +(with-monad sequence-m (domonad [x (range 5) y (range 3)] (+ x y))) -(domonad sequence +(domonad sequence-m [x (range 5) y (range (+ 1 x)) :when (= (+ x y) 2)] @@ -45,7 +45,7 @@ ; An example of a sequence function defined in terms of a lift operation. ; We use m-lift2 because we have to lift a function of two arguments. -(with-monad sequence +(with-monad sequence-m (defn pairs [xs] ((m-lift 2 #(list %1 %2)) xs xs))) @@ -55,14 +55,14 @@ ; a sequence of monadic values and returns a monadic value containing ; the sequence of the underlying values, obtained from chaining together ; from left to right the monadic values in the sequence. -(with-monad sequence +(with-monad sequence-m (defn pairs [xs] (m-seq (list xs xs)))) (pairs (range 5)) ; This definition suggests a generalization: -(with-monad sequence +(with-monad sequence-m (defn ntuples [n xs] (m-seq (replicate n xs)))) @@ -70,13 +70,13 @@ (ntuples 3 (range 5)) ; Lift operations can also be used inside a monad comprehension: -(domonad sequence +(domonad sequence-m [x ((m-lift 1 (partial * 2)) (range 5)) y (range 2)] [x y]) ; The m-plus operation does concatenation in the sequence monad. -(domonad sequence +(domonad sequence-m [x ((m-lift 2 +) (range 5) (range 3)) y (m-plus (range 2) '(10 11))] [x y]) @@ -89,7 +89,7 @@ ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; Maybe monad versions of basic arithmetic -(with-monad maybe +(with-monad maybe-m (def m+ (m-lift 2 +)) (def m- (m-lift 2 -)) (def m* (m-lift 2 *))) @@ -99,7 +99,7 @@ ; is attempted. It is best defined by a monad comprehension with a ; :when clause: (defn safe-div [x y] - (domonad maybe + (domonad maybe-m [a x b y :when (not (zero? b))] @@ -107,7 +107,7 @@ ; Now do some non-trivial computation with division ; It fails for (1) x = 0, (2) y = 0 or (3) y = -x. -(with-monad maybe +(with-monad maybe-m (defn some-function [x y] (let [one (m-result 1)] (safe-div one (m+ (safe-div one (m-result x)) @@ -121,7 +121,7 @@ ; In the maybe monad, m-plus selects the first monadic value that ; holds a valid value. -(with-monad maybe +(with-monad maybe-m (m-plus (some-function 2 0) (some-function 2 -2) (some-function 2 3))) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; @@ -185,7 +185,7 @@ ; In the first version, we call rng 12 times explicitly and calculate the ; shifted sum in a monad comprehension: (def gaussian1 - (domonad state + (domonad state-m [x1 rng x2 rng x3 rng @@ -211,7 +211,7 @@ ; More precisely, we need (m-lift 2 +), because we want both arguments ; of + to be lifted to the state monad: (def gaussian2 - (domonad state + (domonad state-m [sum12 (reduce (m-lift 2 +) (replicate 12 rng))] (- sum12 6.))) @@ -222,7 +222,7 @@ ; We can also do the subtraction of 6 in a lifted function, and get rid ; of the monad comprehension altogether: -(with-monad state +(with-monad state-m (def gaussian3 ((m-lift 1 #(- % 6.)) (reduce (m-lift 2 +) (replicate 12 rng))))) @@ -234,7 +234,7 @@ ; For a random point in two dimensions, we'd like a random number generator ; that yields a list of two random numbers. The m-seq operation can easily ; provide it: -(with-monad state +(with-monad state-m (def rng2 (m-seq (list rng rng)))) ; Let's test it: @@ -243,7 +243,7 @@ ; fetch-state and get-state can be used to save the seed of the random ; number generator and go back to that saved seed later on: (def identical-random-seqs - (domonad state + (domonad state-m [seed (fetch-state) x1 rng x2 rng @@ -261,7 +261,7 @@ ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; A basic logging example -(domonad (writer accu/empty-string) +(domonad (writer-m accu/empty-string) [x (m-result 1) _ (write "first step\n") y (m-result 2) @@ -292,7 +292,7 @@ ; vector accumulator. We can then place calls to write in between the ; steps, and obtain as a result both the return value of the function ; and the accumulated trace values. -(with-monad (writer accu/empty-vector) +(with-monad (writer-m accu/empty-vector) (defn fib-trace [n] (if (< n 2) @@ -329,20 +329,20 @@ ; lead immediately to a nil result in the output. ; First we define the combined monad: -(def seq-maybe (maybe-t sequence)) +(def seq-maybe-m (maybe-t sequence-m)) ; As a first illustration, we create a range of integers and replace ; all even values by nil, using a simple when expression. We use this ; sequence in a monad comprehension that yields (inc x). The result ; is a sequence in which inc has been applied to all non-nil values, ; whereas the nil values appear unmodified in the output: -(domonad seq-maybe +(domonad seq-maybe-m [x (for [n (range 10)] (when (odd? n) n))] (inc x)) ; Next we repeat the definition of the function pairs (see above), but ; using the seq-maybe monad: -(with-monad seq-maybe +(with-monad seq-maybe-m (defn pairs-maybe [xs] (m-seq (list xs xs)))) @@ -369,7 +369,7 @@ ; a function that behaves in the same way, passing 3 to its function ; argument. run-cont executes a continuation by calling it on identity. (run-cont - (domonad cont + (domonad cont-m [x (m-result 1) y (m-result 2)] (+ x y))) @@ -381,7 +381,7 @@ (def continuation nil) (run-cont - (domonad cont + (domonad cont-m [x (m-result 1) y (call-cc (fn [c] (def continuation c) (c 2)))] (+ x y))) @@ -397,7 +397,7 @@ (defn sqrt-as-str [x] (call-cc (fn [k] - (domonad cont + (domonad cont-m [_ (m-when (< x 0) (k (str "negative argument " x)))] (str (. Math sqrt x)))))) |