How to use function argument in a mapping?

Question

Let's take a look at the example below.

function! Print (text)
    echo a:text
endfunction

function! Mapping_test (parameter)
    nnoremap m1 :call Print (a:parameter)<CR>
    nnoremap m2 :call Print ("hello")<CR>
    execute 'nnoremap m3 :call Print ("' . a:parameter . '")<CR>'
    execute 'command! -nargs=0 MTest :call Print ("' . a:parameter . '")'
endfunction

call Mapping_test ("hello world")

m1 mapping produces two errors:

E121: Undefined variable: a:parameter                                                                                                                                                                                                               
E116: Invalid arguments for function Print

m2 and m3 work fine. So calling function with string literal is fine, using execute is also ok, but why m1 does not work?

Basically, I could take m3 and be happy, but if I change argument of Mapping_test() from string literal to an array then m3 does not work either.

call Mapping_test (["hello world"])

produces

E730: Using a List as a String

I even tried to use command, but result is the same, when passing List as a:parameter, error occurs.

So, is there any possible way I can pass argument (here a:parameter) to a function call (in a mapping) which type is not a String?

Answer 1

Mappings always execute in the global context. That is, they don't "remember" that they were defined inside a function, so they can't access a: variables directly.

As for the E730: Using a List as a String error, you can try using type() and join():

function! Mapping_test (parameter)
    nnoremap m1 :call Print (a:parameter)<CR>
    nnoremap m2 :call Print ("hello")<CR>
    execute 'nnoremap m3 :call Print ("' . (type(a:parameter) == type([]) ? join(a:parameter, '') : a:parameter) . '")<CR>'
    execute 'command! -nargs=0 MTest :call Print ("' . (type(a:parameter) == type([]) ? join(a:parameter, '') : a:parameter) . '")'
endfunction