Too few variables specified error when using macros

[Shin Jiraphongtrakul]

Hello everyone, I am trying to figure why does using the generate command with a local results in the error "Too few variables specified", but it works fine when used with a variable?

Below is my code, trying to generate a variable/macro based off of arguments given to be later used in running a DID regression. The problem lies in when generating the `K' macro. It does not work with `K', but works fine with the variable K. Why is this? Thank you for your answers in advance!

program define testfunction, eclass sortpreserve
    version 17.0
    syntax varlist(min=5 max=5)

    /*initialize variables*/
    tokenize `varlist'
    local Y `1'
    local i `2'
    local t `3'
    local ei `4'
    local group `5'

    gen K = (`t' - `ei')
    
end

[Maarten Buis]

generate creates a variable and variables need names. If you type gen `K' = ... then Stata sees a ` and a ', and before it starts executing any commands it first replaces the local macro with its contents. In your program, the local macro `K' is not defined and not defined macros contain empty strings. So what Stata sees next is gen = ... and returns an error message. What you can do is at the beginning of the program define a temporary variable, and use that: tempvar K, now the local macro `K' is defined (with something linke _000000001) you can use `K', and at the end of the program, the variable `K' will be removed.

[Shin Jiraphongtrakul]

thank you for the very clear explanation!