That's much clearer to me now. You've discovered that
-if- and -in- are checked for consistency with the
data in memory. There seem to be two routes to follow.
-gettoken- can look for -if- and pick up what follows.
But that could be several tokens e.g.
if foo > 20 & bar < 10
so you have to keep going until you find an -in-
or a comma. And vice versa.
You read it your dataset and then process the
other stuff. Say
gettoken data 0 : 0
use `data', clear
syntax [if] [in] [, * ]
marksample `touse'
keep if `touse'
...
Nick
[email protected]
David Harrison
>
> You say 'Stata isn't good at extra-sensory perception'
> however the command -use- can manage it...
>
> . clear
>
> . use auto.dta if foreign==1
> (1978 Automobile Data)
>
> . tab foreign
>
> Car type | Freq. Percent Cum.
> ------------+-----------------------------------
> Foreign | 22 100.00 100.00
> ------------+-----------------------------------
> Total | 22 100.00
>
> . clear
>
> . use auto.dta in 1/10
> (1978 Automobile Data)
>
> . count
> 10
>
> The syntax looks standard, but cannot be parsed by the
> -syntax- command. Suppose the program I wanted to write was
> as follows (in reality it is more complex, obviously)...
>
> program foo
> syntax [name] [if] [in] [, *]
> use `namelist'.dta `if' `in' , `options'
> end
>
> Then...
>
> . clear
>
> . foo auto if foreign==1
> foreign not found
> r(111);
>
> . foo auto in 1/10
> Obs. nos. out of range
> r(198);
>
> So what I am trying to work out is how to manually parse the
> input (using -gettoken- and the like) to identify the name
> (if there is one), if statement (if there is one), in
> statement (if there is one) and options (if any are specified).
>
> I could get around it by putting the [if] and [in] as options
> instead, eg
>
> syntax [name] [, ifopt(string) inopt(string) *]
>
> but this goes against the appeal of the intuitive standard
> syntax of Stata, so I wondered if anyone had overcome this
> problem before?
>
> David
> [email protected]
>
> Nick Cox
>
> > I don't however understand the bit about
> > variables not in memory. Stata isn't good
> > at extra-sensory perception...
> >
> > David Harrison
> >
> > > I want to write a command with the syntax
> > >
> > > command [name] [if exp] [in range] [, opt1 opt2 *]
> > >
> > > BUT, the -if exp- and -in range- are to be applied in a -use-
> > > statement, so they may involve variables that are not in the
> > > dataset in memory. Any suggestions on how I can parse this to
> > > get the locals `namelist' `if' `in' `opt1' `opt2' and
> > > `options' that would be produced by -syntax-?
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