Function as_append 

pub fn as_append<C: Cost>(x: Doc<C>, y: Doc<C>) -> Doc<C>

Concatenates two documents horizontally with spacing and alignment.

Similar to a_append, but with a space included between the documents.

To combine more than two documents or an iterator of documents, use as_concat.

Equivalent to x & space() & align(y).

Example

let doc = as_append(nl() & text("hello"),
                    text("my") & nl() & text("friend"));
assert_eq!(doc.to_string(), r"
hello my
      friend");