Add a protected modulo function

arithmetic_rules.pl

@@ -7,7 +7,8 @@
     always_negative/1,
     always_positive/1,
     normalize_number/2,
-    is_null/1
+    is_null/1,
+    modulo/3
   ]).
 
 % Insert here for separate compilation and linting
@@ -788,6 +789,15 @@ is_null_sr(_A^(-_N)) :- !, false.
 is_null_sr(A^_N) :- is_null_sr(A).
 
 
+%! modulo(+A, +B)
+%
+% compute C is mod(A,B) but fail instead of raising an error when A or B are not integer
 
+modulo(A, B, C) :-
+  catch(
+    C is mod(A, B),
+    error(type_error(integer,_n), _context),
+    fail
+  ).
 
 

formal_derivation.pl

@@ -33,12 +33,12 @@ derivate_raw(A - B, Variable, Aprime - Bprime) :-
   derivate_raw(B, Variable, Bprime).
 
 derivate_raw(A * B, Variable, Aprime * B) :-
-  derivate_raw(B, Variable, 0),
+  derivate(B, Variable, 0),
   !,
   derivate_raw(A, Variable, Aprime).
 
 derivate_raw(A * B, Variable, A * Bprime) :-
-  derivate_raw(A, Variable, 0),
+  derivate(A, Variable, 0),
   !,
   derivate_raw(B, Variable, Bprime).
 

formal_derivation.plt

@@ -12,10 +12,13 @@ test('dx/dt(x^2) = 2x', [true(E == 2 * x)]) :-
   derivate(x ^ 2, x, E).
 
 test('dx/dt(cos(sqrt(x))) = - 0.5 / sqrt(x) * sin(sqrt(x))',
-     [true(E == - (1 / sqrt(x) / 2 * sin(sqrt(x))))]) :-
+     [true(E == - ( x^(-0.5) / 2 * sin(sqrt(x))))]) :-
   derivate(cos(sqrt(x)), x, E).
 
 test('derivate quotient', [true(E == -1*x / y^2)]) :-
   derivate(x/y, y, E).
 
+test('derivate real test 1', [true(D == a*c^2)]) :-
+  derivate(a*b*c^2, b, D).
+
 :- end_tests(formal_derivation).