For instance, the OCaml expression (1 + 2) can also be written ((+) 1 2) or (((+) 1) 2). The difference is only at the level of the concrete syntax, since these three versions are equivalent representations of the same abstract syntax tree. As demonstrated by the definition of a revised syntax for OCaml, the same programming language can use different concrete syntaxes. They would all converge to an abstract syntax tree in a unique format that a compiler can handle.