Re: extra data in expressions
- To: mathgroup at smc.vnet.net
- Subject: [mg53375] Re: [mg53367] extra data in expressions
- From: DrBob <drbob at bigfoot.com>
- Date: Sat, 8 Jan 2005 23:02:35 -0500 (EST)
- References: <200501080739.CAA17766@smc.vnet.net>
- Reply-to: drbob at bigfoot.com
- Sender: owner-wri-mathgroup at wolfram.com
>> Why does Head[String @@ 1] return Integer? Because you can't replace the head of an "atomic" expression. ToString changes expressions to strings, if that's what you wanted to do. >> What else could it possibly return? Exactly. > I'm starting to suspect that "everything is an expression" involves > some pretty ugly exceptions. Perhaps, but you haven't mentioned any so far. Bobby On Sat, 8 Jan 2005 02:39:36 -0500 (EST), <joshuahorowitz at comcast.net> wrote: > Here's a rather abstract foundations question: > > I once unthinkingly assumed that an expression was determined by its > head and parts. This is of course very wrong: any two expressions with > head Real, no matter how different, have head Real and no parts. Same > goes for Symbol, Integer, String, and all other "atomic" expression > heads. This means that certain expressions can (and must) hold hidden > extra data. > > My question is whether there are any consistent, logical semantics for > this extra data. Can an expression contain both parts AND extra data? > Which built-in symbols (or rather, expressions with head one of these > built-in symbols) contain extra data; is there a list somewhere? Can > user-defined symbols contain user-defined extra data? Why does > Head[String @@ 1] return Integer? What else could it possibly return? > > I'm starting to suspect that "everything is an expression" involves > some pretty ugly exceptions. > > > > -- DrBob at bigfoot.com www.eclecticdreams.net
- References:
- extra data in expressions
- From: joshuahorowitz@comcast.net
- extra data in expressions