Remove unnecessary state monad implementation

(monad 'state) is synonymous with (transformer 'state 'identity). The
monad macro has been updated to reflect that.

include/monads.lfe

@@ -1,7 +1,11 @@
 (defmacro monad (name)
-  `(list_to_atom (lists:flatten (list "calrissian-"
-                                      (atom_to_list ,name)
-                                      "-monad"))))
+  (case name
+    ;; Provide the state monad in terms of the state transformer
+    (''state `(transformer 'state 'identity))
+    (_
+     `(list_to_atom (lists:flatten (list "calrissian-"
+                                         (atom_to_list ,name)
+                                         "-monad"))))))
 
 (defmacro transformer (name inner-monad)
   `(tuple (list_to_atom (lists:flatten (list "calrissian-"

src/calrissian-state-monad.lfe

@@ -1,47 +0,0 @@
-(defmodule calrissian-state-monad
-  (behaviour calrissian-monad)
-  (behaviour calrissian-state)
-  (export (return 1)
-          (fail 1)
-          (run 2)
-          (>>= 2)
-          (get 0)
-          (put 1)
-          (modify 1)
-          (modify-and-return 1)
-          (exec 2)
-          (eval 2)))
-
-(defun return (x) (lambda (state) (tuple x state)))
-(defun fail (x) (throw (tuple 'error x)))
-
-(defun run (m state)
-  (funcall m state))
-
-(defun >>= (m f)
-  (lambda (state)
-    (let (((tuple x s) (run m state)))
-      (run (funcall f x) s))))
-
-(defun put (state)
-  (lambda (_) (tuple '() state)))
-
-(defun get ()
-  (lambda (state)
-    (tuple state state)))
-
-(defun modify (f)
-  (lambda (state)
-    (tuple '() (funcall f state))))
-
-(defun modify-and-return (f)
-  (lambda (state)
-    (let ((newstate (funcall f state)))
-      (tuple newstate newstate))))
-
-(defun eval (m state)
-  (let (((tuple x _s) (run m state)))
-    x))
-(defun exec (m state)
-  (let (((tuple _x s) (run m state)))
-    s))

test/unit/unit-calrissian-state-monad-tests.lfe

@@ -1,12 +0,0 @@
-(defmodule unit-calrissian-state-monad-tests
-  (export all)
-  (import
-    (from lfeunit-util
-      (check-failed-assert 2)
-      (check-wrong-assert-exception 2))))
-
-(include-lib "deps/lfeunit/include/lfeunit-macros.lfe")
-(include-lib "include/monads.lfe")
-(include-lib "include/monad-tests.lfe")
-
-(test-monad (monad 'state))