add modulo function

cogs/r5rs.scm

@@ -294,13 +294,14 @@
 
 ;; TODO: Adjust the below check-equals
 
-(skip-compile (check-equal 1 (modulo 13 4))
-              (check-equal 1 (remainder 13 4))
-              (check-equal 3 (modulo -13 4))
+(check-equal? "modulo positive numbers" 1 (modulo 13 4))
+(check-equal? "modulo negative and positive" 3 (modulo -13 4))
+(check-equal? "modulo positive and negative" -3 (modulo 13 -4))
+(check-equal? "modulo both negative" -1 (modulo -13 -4))
+
+(skip-compile (check-equal 1 (remainder 13 4))
               (check-equal -1 (remainder -13 4))
-              (check-equal -3 (modulo 13 -4))
               (check-equal 1 (remainder 13 -4))
-              (check-equal -1 (modulo -13 -4))
               (check-equal -1 (remainder -13 -4))
               (check-equal 4 (gcd 32 -36))
               (check-equal 288 (lcm 32 -36)))

crates/steel-core/src/primitives/numbers.rs

@@ -366,6 +366,31 @@ pub fn quotient(args: &[SteelVal]) -> Result<SteelVal> {
     }
 }
 
+/// Returns the remainder of the division of the first number by the second
+///
+/// (modulo n m) -> integer?
+///
+/// * n : integer?
+/// * m : integer?
+///
+/// # Examples
+/// ```scheme
+/// > (modulo 10 3) ;; => 1
+/// > (modulo -10 3) ;; => 2
+/// > (modulo 10 -3) ;; => -2
+/// > (module -10 -3) ;; => -1
+/// ```
+#[steel_derive::native(name = "modulo", constant = true, arity = "Exact(2)")]
+pub fn modulo(args: &[SteelVal]) -> Result<SteelVal> {
+    match &args {
+        [l, r] => match (l, r) {
+            (SteelVal::IntV(l), SteelVal::IntV(r)) => ((l % r + r) % r).into_steelval(),
+            _ => steelerr!(TypeMismatch => "quotient only supports integers"),
+        },
+        _ => steelerr!(ArityMismatch => "quotient requires 2 arguments"),
+    }
+}
+
 /// Divides the given numbers.
 ///
 /// (/ . nums) -> number?

crates/steel-core/src/steel_vm/engine.rs

@@ -1501,6 +1501,7 @@ impl Engine {
         })
     }
 
+    // TODO: Remove duplicates!
     pub fn readable_globals(&self, after_offset: usize) -> Vec<InternedString> {
         self.virtual_machine
             .compiler

crates/steel-core/src/steel_vm/primitives.rs

@@ -1070,6 +1070,7 @@ fn number_module() -> BuiltInModule {
         .register_native_fn_definition(numbers::MAGNITUDE_DEFINITION)
         .register_native_fn_definition(numbers::NUMERATOR_DEFINITION)
         .register_native_fn_definition(numbers::QUOTIENT_DEFINITION)
+        .register_native_fn_definition(numbers::MODULO_DEFINITION)
         .register_native_fn_definition(numbers::ROUND_DEFINITION)
         .register_native_fn_definition(numbers::SQUARE_DEFINITION)
         .register_native_fn_definition(numbers::SQRT_DEFINITION);