closure - computer science vs. mathematics

0,closure in computer science.
In computer science, a closure (also lexical closure or function closure) is a function or reference to a function together with a referencing environment. – Wikipedia

1,closure in mathematics.
A set has closure under an operation if performance of that operation on members of the set always produces a member of the same set. – Wikipedia

2, the core functions of foolang should make up a closure in meaning of mathematics.
2.0, option-1: to keep the existing relatively complex structure.
2.0, option-2: to reduce it to a simple model.- like lisp?