lua call conversion rules

lua-call

tarantool> function foo() return end
---
...

tarantool> c:call('foo')
---
- []
...

tarantool> function foo() return nil end
---
...

tarantool> c:call('foo')
---
- - [null]
...

tarantool> function foo() return 1 end
---
...

tarantool> c:call('foo')
---
- - [1]
...

tarantool> function foo() return 1, 2, 3 end
---
...

tarantool> c:call('foo')
---
- - [1]
  - [2]
  - [3]
...

tarantool> function foo() return {} end
---
...