Considerations

• There's no need to capture free variables in a set, because that's only necessary for compiled languages. Since the lambda expressions are interpreted on the fly, they capture the surrounding context correctly.
  • It follows that there's no need to parse both forms of the lambda, and that only the basic [H|T]>>Lambda form is necessary.
• Macro expansion is not necessary because lambdas simply return the result of invoking call/* directly.
  • Still, built-in resolution was improved to make sure that it's possible to return a term to be recursively resolved as another built-in, rather than just returning a term that is then going to be evaluated as a goal.
• Creating an abstract type for lambdas turned out to be rather pointless, because there's never really a need to access their abstract form; also it created some parsing issues with comma expressions, so it wasn't included.

from ergo.