koans - triangle

using cond, which is ok (destructuring would be nice)
and signaling errors, copying definitions of errors

and not quite proficient with writing code that has guards against errors

lisp-koans/koans/triangle-project.lisp

@@ -14,11 +14,24 @@
 
 (define-condition triangle-error (error)
   ;; Fill in the blank with a suitable slot definition.
-  (____))
+  ((triangle-error-sides :initarg :sides :reader triangle-error-sides)))
 
 (defun triangle (a b c)
   ;; Fill in the blank with a function that satisfies the below tests.
-  ____)
+  (cond
+    ((or (<= a 0) (<= b 0) (<= c 0)) (signal (make-condition 'type-error
+                                                      :datum (car (remove-if-not (lambda (n) (>= 0 n)) (list a b c)))
+                                                      :expected-type '(real (0)))))
+    ((or (<= (+ a b) c) (<= (+ b c) a) (<= (+ a c) b)) (signal (make-condition 'triangle-error
+                                                                               :sides (list a b c))))
+    ((= a b c) :equilateral)
+    ((or (= a b) (= b c) (= a c)) :isosceles)
+    (t :scalene)))
+
+(car (remove-if (lambda (n) (>= 0 n)) (list 1 2 -2)))
+
+(triangle 1 1 1)
+(triangle 0 0 0)
 
 (define-test equilateral-triangles
     ;; Equilateral triangles have three sides of equal length,
@@ -39,6 +52,18 @@
   (assert-equal :scalene (triangle 10 11 12))
   (assert-equal :scalene (triangle 5 4 2)))
 
+(defun triangle-failure (a b c)
+           (handler-case (progn (triangle a b c) (error "Test failure"))
+             (error (condition) condition)))
+(triangle 0 0 0)
+(setq condi (triangle-failure 2 -1 1))
+(type-error-datum condi)
+(type-error-expected-type condi)
+
+(setq condi (triangle-failure 2 4 2))
+(triangle-error-sides condi)
+
+
 (define-test illegal-triangles
     ;; Not all triplets make valid triangles.
     (flet ((triangle-failure (a b c)