extend_syntax
    DefaultSeparator ::= /((?s:\s|%|#[^\n|][^\n]*|#\|.*?\|#)*)/ ;
in
extend_syntax
    Expr ::=also forall T S . '{[
        lhs := (,{Expr<T>},)
        lit ,{DefaultToken}, = '>=>'
        rhs := (,{Expr< [T -> S] >},)
    ]}' function_pipe -> .{
        '[Expr | (,[rhs], ,[lhs],) ]'
    }. ;
    # This has a couple of limitations at the moment.
    # Unseemly still needs support for n-ary function types before you can do
    #   one >=> (plus one)
    # And it also lacks support for operator precedence,
    #  so you need to create a bunch of new nonterminals if you want precedence.
in
  (plus one one) >=> zero?