• cl-webengine - QtWebEngine binding for Common Lisp Bindings to Qt and WebEngine.

• How it Works Common Lisp has a way to interact with C code via the so called CFFI (C Foreign Function Interface). This interface allows any C code to be called by Common Lisp. At this time, there is no universal foreign function interface for C++. This presents a problem when we wish to call Qt code (which is written in C++).

In order to circumvent this problem, we can write functions in C that call the C++ code that we need. Concretely it looks like this:

• =interface.h= we declare a function to wrap some C++ function we want to use.
• =interface.cpp= we implement the C function declared in =interface.h= with the C++ code inside of it.
• =interface.lisp= we implement a definition via CFFI so that Lisp code can call the function defined in =interface.cpp=

In this way, we can now invoke C++ through Lisp. A concrete example is shown below for a single function:

** interface.h

+NAME: interface.h

+BEGIN_SRC C++

extern "C" void widgetShow(void* widget);

+END_SRC

** interface.cpp

+NAME: interface.cpp

+BEGIN_SRC cpp

void widgetShow(void widget) { QWidget _widget = reinterpret_cast<QWidget*>(widget); _widget->show(); }

+END_SRC

** interface.lisp

+NAME: interface.lisp

+BEGIN_SRC lisp

(defcfun ("widgetShow" widget-show) :void (widget :pointer)) (export 'widget-show)

+END_SRC

• Dependencies

The library requires Qt5 and Qt5 Webengine. More specifically, you don't need all of Qt5, the following Qt5 components are enough:

• qtbase

• qtwebengine

• qtwebchannel

• qtdeclarative

• Compilation

  +NAME: compilation

  +BEGIN_SRC shell

  make all

  +END_SRC

After compiling, you will need to copy the shared libraries to a location where CFFI can find them. If you need to append a location for CFFI, you can add the following lines to your Lisp initialization:

+NAME: sbclrc

+BEGIN_SRC lisp

(ql:quickload :cffi) (pushnew "/opt/local/lib/" cffi:foreign-library-directories :test #'equal)

+END_SRC

The above demonstrates an example in SBCL, where the location of the shared library will be in =/opt/local/lib=.

• Running in SBCL on macOS:

  +NAME: configuration

  +BEGIN_SRC lisp

  (sb-int:with-float-traps-masked (:invalid :inexact :overflow) (cl-webengine::run))

  +END_SRC

• Running from SLIME in SBCL on macOS:

  +NAME: configuration

  +BEGIN_SRC lisp

  (trivial-main-thread:call-in-main-thread (lambda () (sb-int:with-float-traps-masked (:invalid :inexact :overflow) (cl-webengine::run))))

  +END_SRC