Evaluate Ruby expression {expr} and return its result converted to Vim data structures. Numbers, floats and strings are returned as they are (strings are copied though). Arrays are represented as Vim |List| type. Hashes are represented as Vim |Dictionary| type. Other objects are represented as strings resulted from their "Object#to_s" method. Note that in a :def function local variables are not visible to {expr}. Can also be used as a |method|: GetRubyExpr()->rubyeval() {only available when compiled with the |+ruby| feature}