Re: Low-Rent Syntax

In article <1990Aug09.180536.18782@esegue.segue.boston.ma.us> Donald Lindsay writes:
>In article <1990Jul27.034115.8747@esegue.segue.boston.ma.us>
> moss@cs.umass.edu (Eliot Moss) writes:
>>CLU was actually able to *eliminate* the ";" statement separator/terminator,
>>through *very* careful syntax design (and maybe it required more than one
>>token look-ahead, too; I don't recall clearly).
>
>The Icon language (Arizona) and the Turing language (Toronto) both
>have "low rent" syntax - that is, the ";" is only needed (as a
>separator) when one writes multiple statements on a single line. In
>all other cases, it can be omitted.
>
>Is there now a "usual" way to implement this ?


In Turing, the semicolon is never needed. The reason is careful syntax
design. There is no trickery in the lexical analysis and the grammar
is LL(1). Consider the following LL(1) grammar
SS -->
| S SS
S --> var name : T
| procedure name A SS end name
| function name A : T SS end name
| E := E
| if E then SS [else SS] end if
| case E of {label E: SS} [label : SS] end case
| loop SS end loop
| for name : T SS end for
| exit [when E]
E --> etc
T --> etc
A --> etc
No semicolons. In Turing the second clause is really
SS --> S [ ; ] SS
So you can sprinkle semicolons to taste. Euclid had a similar syntax,
but a semicolon was still required in one obscure case.


In Icon, the newline takes the place of the semicolon when a semicolon
is syntactically allowed. This means you have to write
a := b +
c
rather than
a := b
+ c
if you mean
a := b + c
The second is syntactically correct, but means something else. Griswold has
a book on the implementation of Icon. Perhaps it explains the
implementation of this rule.


I haven't a clue about CLU.


Theo Norvell
U of T
--

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