Fix function evaluation when parameter list is only one parameter

``
let f: R->R, (x)->x+1;
f(2);
``
was complaining that the function parameter was not of the correct type (git
language::parameter_list instead of language::name)

src/language/ASTNodeFunctionExpressionBuilder.cpp

@@ -81,7 +81,8 @@ ASTNodeFunctionExpressionBuilder::_buildArgumentProcessors(FunctionDescriptor& f
 
   ASTNode& argument_nodes = *node.children[1];
 
-  const size_t arguments_number = argument_nodes.is_type<language::expression_list>() ? argument_nodes.children.size() : 1;
+  const size_t arguments_number =
+    argument_nodes.is_type<language::expression_list>() ? argument_nodes.children.size() : 1;
   const size_t parameters_number =
     parameter_variables.is_type<language::name_list>() ? parameter_variables.children.size() : 1;
 
@@ -98,10 +99,14 @@ ASTNodeFunctionExpressionBuilder::_buildArgumentProcessors(FunctionDescriptor& f
       ASTNode& argument_node      = *argument_nodes.children[i];
       this->_storeArgumentProcessor(parameter_variable, argument_node, function_processor);
     }
+  } else {
+    if (parameter_variables.is_type<language::name_list>()) {
+      this->_storeArgumentProcessor(*parameter_variables.children[0], argument_nodes, function_processor);
     } else {
       this->_storeArgumentProcessor(parameter_variables, argument_nodes, function_processor);
     }
   }
+}
 
 PUGS_INLINE
 std::unique_ptr<INodeProcessor>