Added sub to the builtin functions.

src/builtin.c

@@ -21,3 +21,27 @@ AST* builtin_sum(size_t argc, AST** argv) {
 
     return ast_init(AST_TYPE_NUM, ast_num_data_init(total));
 }
+
+AST* builtin_sub(size_t argc, AST** argv) {
+    log_dbg("Got here");
+    AST* first = *argv;
+    if (first->type != AST_TYPE_NUM)
+        return ast_init(
+            AST_TYPE_EXC, ast_exc_data_init("Can't subtract non-num arguments.")
+        );
+
+    ASTNumData total = *(ASTNumData*)first->data;
+
+    for (int i = 1; i < argc; i++) {
+        AST* arg = argv[i];
+        if (arg->type != AST_TYPE_NUM)
+            return ast_init(
+                AST_TYPE_EXC,
+                ast_exc_data_init("Can't subtract non-num arguments.")
+            );
+
+        total -= *(ASTNumData*)arg->data;
+    }
+
+    return ast_init(AST_TYPE_NUM, ast_num_data_init(total));
+}

src/exec.c

@@ -22,6 +22,10 @@ AST* exec_start(AST* ast) {
         global, "sum", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_sum))
     );
 
+    htab_ins(
+        global, "sub", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_sub))
+    );
+
     // Push global namespace to `scope`.
     stack_push(scope, global);
 
@@ -74,7 +78,7 @@ AST* exec_call(AST* ast) {
         case AST_TYPE_BIF:
             ASTBIFData bifdata = fdef->data;
             return bifdata(argc, argv);
-        default: return ast_init(AST_TYPE_EXC, ast_exc_data_init("Good job"));
+        default: return ast_init(AST_TYPE_EXC, ast_exc_data_init("Good job!"));
     }
 }
 

src/include/builtin.h

@@ -6,7 +6,12 @@
 // Sum some nums.
 AST* builtin_sum(size_t argc, AST** argv);
 
+// Subtract nums.
+AST* builtin_sub(size_t argc, AST** argv);
+
 // The list of built-in functions.
-static AST* (*builtin_fns[])(size_t argc, AST** argv) = {builtin_sum};
+static AST* (*builtin_fns[])(size_t argc, AST** argv) = {
+    builtin_sum, builtin_sub
+};
 
 #endif