st: nested loops with varying degrees of nesting

[David Kantor <kantor.d@att.net>]

Hello all,
I would like to write a program that involves nested loops, where the 
degree of nesting is flexible.
Consider the following simplified shell of a program. c1, c2, c3 are 
options that, for each one that is present, an additional a level of 
looping should be invoked.

prog def t1
syntax , [c1 c2 c3]

if "`c1'" ~= "" {
	local loop1 "forvalues d1 = 1/4 {"
	local loop1end "}"
}

if "`c2'" ~= "" {
	local loop2 "forvalues d2 = 1/4 {"
	local loop2end "}"
}

if "`c3'" ~= "" {
	local loop3 "forvalues d3 = 1/4 {"
	local loop3end "}"
}

`loop1'
`loop2'
`loop3'
disp "`d1' `d2' `d3'"
`loop3end'
`loop2end'
`loop1end'

end

----

When this runs, with one or more of the c1,c2,c3 options, I get
unrecognized command:  } invalid command name
--just the same as when I type
}
in the command window.
Evidently, a macro can stand for a command, but not "}"  -- or "}" is 
not a command..

Does anyone have an Idea of how to accomplish this goal? I do have 
one idea, involving counting the number of loops:
if num_loops==1 {
	forvalues d1 = 1/4 {
	do_stuff
	}
}
else if num_loops==2 {
	forvalues d1 = 1/4 {
		forvalues d2 = 1/4 {
		do_stuff
		}
	}
else if num_loops==3 {
	forvalues d1 = 1/4 {
		forvalues d2 = 1/4 {
			forvalues d3 = 1/4 {
			do_stuff
			}
		}
	}
}

-- but I'd rather do something more succinct, if possible; my actual 
program may have up to 8 levels of nesting.
Does anyone have a suggestion?
(I do have another idea: build the entire nested looping command into 
one macro; I have not tried this yet.)
I use Stata 10.
Thanks
--David

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