Modula-3: With statements

# With

A `WITH` statement has the form:

        WITH id = e DO S END

where `id` is an identifier, `e` an expression, and `S` a statement. The statement declares `id` with scope `S` as an alias for the variable `e` or as a readonly name for the value `e`. The expression `e` is evaluated once, at entry to the `WITH` statement.

The statement is like the procedure call `P(e)`, where `P` is declared as:

        PROCEDURE P(mode id: type of e) = BEGIN S END P;

If `e` is a writable designator, `mode` is `VAR`; otherwise, `mode` is `READONLY`. The only difference between the `WITH` statement and the call `P(e)` is that free variables, `RETURN`s, and `EXIT`s that occur in the `WITH` statement are interpreted in the context of the `WITH` statement, not in the context of `P`.

A single `WITH` can contain multiple bindings, which are evaluated sequentially. That is:

        WITH id_1 = e_1, id_2 = e_2, ...

is equivalent to:

        WITH id_1 = e_1 DO
          WITH id_2 = e_2 DO ....

    Last modified on Wed Apr  3 09:38:51 PST 1996 by heydon
         modified on Mon Dec 19 08:18:03 PST 1994 by kalsow