定义为计算宏的语法类别（意识）？

Question

I want to create two macros that use the same match expression but are distinguished by their syntactic category, ie action or expression. For example I want to express

var x := obj.foo(); // value-returning
...
obj.foo(); // not value-returning

Using the following macro definitions:

define <my_macro_void_call'action> "<obj'exp>.foo" as computed {
   <if in expression context>
     reject_match()
   <else>
     do_something
};

define <my_macro_call'expr> "<obj'exp>.foo" as computed {
   <if in action context>
     reject_match()
   <else>
     do_something
};

Is this possible at all? I know that I can use "compute" to call a value-returning method in a void context, but it is not as nice.

Answer 1

You don't need to ask in what context the macro was matched, because the interpreter will handle that for you. Here's an example with a function that either returns TRUE in expression context or prints out something in action context:

define <my_macro_void_call'action> "some_function" as computed {
  print "matched in action context";
  result ="out(\"here I am in action context\");";
};

define <my_macro_call'exp> "some_function" as computed {
  print "matched in expression context";
  result = "TRUE";
};

The interpreter will know which one to expand depending on the context where some_function is seen in:

extend sys {
  run() is also {
    some_function;

    if some_function {
      out("here I was used in expression context");
    }
  };
};

You can easily modify these macros to take an object to call a method on.