String concatenation

[jerome falken]

Stata15/Linux64
I was trying to find a solution to this problem in the forums, but I'm still running into this issue when using various strings:

local a1 "v[\`i']<\`l' (v[\`i']-1)<\`l' v[\`i']<10"

works

local a1 "v[\`i']<\`l'" + "(v[\`i']-1)<\`l'" + "v[\`i']<10"

works, but di "`a1'" fails.

local a1 "v[\`i']<\`l' ///
(v[\`i']-1)<\`l' v[\`i']<10"

doesn't work

local a1 ""v[\`i']<\`l'" ///
"(v[\`i']-1)<\`l'" "v[\`i']<10""

doesn't work

local a1 "v[\`i']<\`l'" + ///
"(v[\`i']-1)<\`l'" + ///
"v[\`i']<10"

works, but di "`a1'" fails, and most importantly, I couldn't "word 2 of `a1'" then use it as a condition in a if statement.

Please help me understand how the parser works, and what would be the best approach to format this do file properly, my intend is to use "///" which I think is easier to read, also that I would prefer not to use such format, which is more difficult to read and (I think) cumbersome.

local a1 "v[\`i']<\`l'"
local a1"`a1' (v[\`i']-1)<\`l'"
local a1"`a1' v[\`i']<10"

works

[Attaullah Shah]

Here is one approach for the three slashes

loc i = 1
loc 1  one
local a1 v[\`i']<\`l'  ///
(v[\`i']-1)<\`l' + ///
v[\`i']<10
di "`a1'"
v[1]<  (v[1]-1)< + v[1]<10

For your second line

 loc i = 1
loc 1  one
local a1 "v[\`i']<\`l' + (v[\`i']-1)<\`l' + v[\`i']<10"
di `"`a1'"'
v[1]< + (v[1]-1)< + v[1]<10

[jerome falken]

I don't think this will work in my case because at the time the local is defined, nether value (v, i, l) is defined, which is why I kept things as strings.

[Attaullah Shah]

OK, I got it. So if you do not want your macro to expand, then use the slash (escape character) with the macro name as well. See for example

local a1 v[\`i']<\`l'
di "\`a1'"
`a1'

More on this here https://www.stata.com/support/faqs/p...es-and-macros/

So when v, l, and i are not defined, do not expand it, once they are available, then expand

loc a v[\`i']<\`l' + (v[\`i']-1)<\`l' + v[\`i']<10

dis "\`a'"
`a'
loc i = 5
loc l = 6
dis "`a'"
v[5]<6 + (v[5]-1)<6 + v[5]<10

[jerome falken]

Oh this is perfect, thank you!

[Nick Cox]

This kind of code is very hard to write and hard to read later even if you wrote it. It's next to impenetrable for anyone else to read, which may not matter if you're the only programmer in sight. My guess is that you are used to giving lots of definitions at the head of code as a matter of programming style other languages. I'd flag for you

help include

as a way to put your definitions somewhere special and then use them when you want to.

[jerome falken]

One more question Dr Shah,

If I wanted to use globals so the scope could be visible from all functions (program), would I do this?

global g1 v[\`i']<\`l' ///
(v[\`i']-1)<\`l' + ///
v[\`i']<10
di "`a1'"

program def myprog
  local l1 "\$a1"
  [...] do great things [...]
end

[Attaullah Shah]

If I have correctly understood your question ...

global g1 v[\`i']<\`l' ///
(v[\`i']-1)<\`l' + ///
v[\`i']<10

cap prog drop myprog
program def myprog
  local l1 "\$g1"
  loc l = 5
  loc i =6
  di "`l1'"
end
myprog
v[6]<5 (v[6]-1)<5 + v[6]<10

[jerome falken]

Thank you Dr Shah