Proc is older, but the semantics of return are highly counterintuitive to me (at least when I was learning the language) because:

1. if you are using proc, you are most likely using some kind of functional paradigm
2. proc can return out of the enclosing scope (see previous responses), which is a goto basically, and highly non-functional in nature

Lambda is functionally safer and easier to reason about - I always use it instead of proc.

Proc is older, but the semantics of return are highly counterintuitive to me (at least when I was learning the language) because:

1. If you are using proc, you are most likely using some kind of functional paradigm.
2. Proc can return out of the enclosing scope (see previous responses), which is a goto basically, and highly non-functional in nature.

Lambda is functionally safer and easier to reason about - I always use it instead of proc.