Add subtractions handling and re-order

larcs.org

@@ -453,7 +453,7 @@ Equality of constants is a bit different, and is checked as follows:
        (slot-value expression-b 'value)))
 #+END_SRC
 
-** WORKING Compound Types [5/7]
+** WORKING Compound Types [6/7]
 :PROPERTIES:
 :ID:       a0d2eb19-8a1e-4dee-9b41-c454a49cacc4
 :END:
@@ -497,6 +497,34 @@ CLOSED: [2019-01-05 Sat 16:00]
                                :test #'eqal)))))
 #+END_SRC
 
+*** DONE Subtractions
+CLOSED: [2019-01-05 Sat 16:41]
+:PROPERTIES:
+:ID:       aad16971-81c8-48da-aaa5-bb84b03d6912
+:END:
+
+Subtractions again, contain only a list of terms.  However, unlike other types having only a list of terms, the terms are not a set, and therefore order as well as content must be verified to check ~eqal~-ness.
+
+#+Caption: Subtractions
+#+Name: type-subtractions
+#+BEGIN_SRC lisp 
+  @export
+  (defclass <subtraction> (<compound>)
+    ((terms :reader terms
+            :initarg :terms
+            :type (list <expression>))))
+
+  (defmethod eqal ((expression-a <subtraction>) (expression-b <subtraction>))
+    (let ((a-terms (terms expression-a))
+          (b-terms (terms expression-b)))
+      (and (= (length a-terms)
+            (length b-terms))
+         (do* ((keep (eqal (first a-terms) (first b-terms)) (eqal (first a) (first b)))
+               (a a-terms (rest a))
+               (b b-terms (rest b)))
+              ((or (not keep) (null a) (null b)) keep)))))
+#+END_SRC
+
 *** DONE Multiplications
 CLOSED: [2019-01-05 Sat 12:17]
 :PROPERTIES:
@@ -626,8 +654,6 @@ CLOSED: [2019-01-05 Sat 15:47]
 
 *** TODO Trigonometric
 
-*** TODO Subtractions
-
 ** DONE Blended Types -- Polynomial Terms
 CLOSED: [2019-01-05 Sat 09:46]
 :PROPERTIES:
@@ -2053,6 +2079,7 @@ As all of the packages are defined centrally, this makes resolving inter-package
 
   <<type-compound>>
   <<type-additions>>
+  <<type-subtractions>>
   <<type-multiplications>>
   <<type-division>>
   <<type-exponentials>>