isomorphic languages

[Keith Bierman - Sun Tactical Engineering]

In article <75326 at sun.uucp> dgh%dgh at Sun.COM (David Hough) writes:
>Thesis:  Language designers (including X3Jn committees) needn't
>incorporate every bad syntax of the past if revised versions are
>syntactically isomorphic.
>
>  < stuff deleted >
>I'd consider Fortran-8x to be upwardly compatible with Fortran-77, and
>X3J11 C to be upwardly compatible from K&R, if every legal old program
>could be converted to a legal new program by a "context-free"
>translator that only has to look at one logical input line at a time.
>One logical input line may contain multiple physical input lines -
>Fortran-77 continuation lines are what I have in mind.  Languages with
>this "context-free translatability" property could be called
>"syntactically isomorphic".
>
< more stuff deleted >

I agree, but with one modest addition. The translator must be
bidirectional. If a program does not use any of the languages new
features (that don't correspond to anything in the old language), it
should be convertable back into an old format. 

This is necessary for supporting multi-platform projects, where one
cannot be sure that all vendors will supply a new compiler in a timely
fashion. 

Also if the original program was readable (well indented, and
commented, etc.) the converted (or doubly converted) should still be.

With these two proviso's added, I agree with David's proposal.

Keith H. Bierman
It's Not My Fault ---- I Voted for Bill & Opus