Add asserts to check for the first element of the list in def and fn forms

include/serene/exprs/def.h

@@ -53,6 +53,9 @@ public:
   maybe_node analyze(reader::SemanticContext &);
 
   static bool classof(const Expression *e);
+
+  /// Create a Def node out a list. The list should contain the
+  /// correct `def` form like `(def blah value)`.
   static maybe_node make(List *);
   ~Def() = default;
 };

include/serene/exprs/fn.h

@@ -57,6 +57,10 @@ public:
   maybe_node analyze(reader::SemanticContext &);
 
   static bool classof(const Expression *e);
+
+  /// Creates a function node out of a function definition
+  /// in a list. the list has to contain the correct definition
+  /// of a function, for exmaple: `(fn (args1 arg2) body)`
   static maybe_node make(List *);
   ~Fn() = default;
 };

src/serene/exprs/def.cpp

@@ -54,6 +54,10 @@ maybe_node Def::make(List *list) {
         &errors::DefWrongNumberOfArgs, list->elements[0], msg));
   }
 
+  Symbol *defSym = llvm::dyn_cast<Symbol>(list->elements[0].get());
+  assert((defSym && defSym->name == "def") &&
+         "The first element of the list should be a 'def'.");
+
   Symbol *binding = llvm::dyn_cast<Symbol>(list->elements[1].get());
 
   if (!binding) {

src/serene/exprs/fn.cpp

@@ -56,6 +56,10 @@ maybe_node Fn::make(List *list) {
         &errors::FnNoArgsList, list->elements[0], msg));
   }
 
+  Symbol *fnSym = llvm::dyn_cast<Symbol>(list->elements[0].get());
+  assert((fnSym && fnSym->name == "fn") &&
+         "The first element of the list should be a 'fn'.");
+
   List *args = llvm::dyn_cast<List>(list->elements[1].get());
 
   if (!args) {