Vim vmap, send selected text as parameter to function - function

Question

In brief, having written some functions to save typing I'm trying to set up a vmap[ping] that will allow me to select something I typed, and pass this selection to a function (since typing the function call on the command line, typing the parameters (with quotes), and escaping backslashes etc... counteracts most of the time saved by calling functions)
For (a simple) example, supposing I had the following function
func Test(iStr)
if a:iStr[0] =~ [a-zA-z]
echo "hello"
else
echo "hello world"
endif
endfunc
I'd like to be able to visual select some text and then with some key mapping, F2 say, it will call Test(iStr) with the selection serving as the parameter iStr
I believe, that with more work (i.e. some way to specify that what I've selected should be inside Test()), the following
vmap <F2> :call Test()
is what I'm after. Thing is I've tried a number of variants (guesswork plus a little bit of dodgy inference from :help map) and I'm not getting anything useful. Update, I've tried using a helper function Test2() with just
call Test(<C-W>)
as its body...somehow I think I need to grab hold of the word under my cursor (somehow) and then I'm done - since I can pass that to Test(...) from within Test2
As for an actual example of a function I want to call, the following (incomplete yet) function (and helper functions) would allow me to convert an expression of the form, say,
f_k^{(j)}g
to
f_1^{(j)}g, f_2^{(j)}g, \dots, f_{n-1}^{(j)}g, f_n^{(j)}g
In terms of a procedure I want to
a) type the repeated term in vim
b) visually select it
c) hit some mapping key that will call SumOrSequence(iExpression, iIndex)
d) provide "k" as a parameter
e) press enter
f) see the change made by SumOrSequence(...)
The code for SumOrSequence(...) is as follows:
func SumOrSequence(iExpression, iIndex)
"need to check validity of these - maybe set a default
let default = Interrogate("do with defaults? yes [y] (2,1,n,0,\",\"), yes but specify last term [d[a-Z]], no [n]")
if default == "y"
let leftTerms = 2
let rightTerms = 1
let lastTermIndex = "n"
let firstTermIndex = 0
let operator = ","
let dotType = "\\dots"
elseif default =~ 'd[a-zA-Z]'
let leftTerms = 2
let rightTerms = 1
let lastTermIndex = default[1]
let firstTermIndex = 0
let operator = Interrogate("what separates terms? add [+], subtract [-], times [*], comma [,], ampersand [&]?")
let dotType = "\\cdots"
else "so n or anything else
let leftTerms = InterrogateNumber("how many terms before dots? ")
let rightTerms = InterrogateNumber("how many terms after dots? ")
let lastTermIndex = Interrogate("what is last term index?")
let firstTermIndex = Interrogate("what is first term index?")
let operator = Interrogate("what separates terms? add [+], subtract [-], times [*], comma [,], ampersand [&]?") "need to check only any of these provided
let dotType = "\\cdots"
endif
if operator == ","
let dotType = "\\dots"
endif
if operator == "*"
let operator = "\\times"
endif
let leftCount = 0
let oExpression = ""
while leftCount < leftTerms
if leftCount > 0
let oExpression .= operator . " "
endif
let oExpression .= ReplaceIndex(a:iExpression, a:iIndex, leftCount,1)
let leftCount += 1
endwhile
let oExpression .= operator . " " . dotType . " "
let rightCount = rightTerms-1
while rightCount > 0
"here we are going to be counting backwards from some number denoting number of terms - may need to know if we actually have a number!
echo "decrement: " . HandleDecrement(lastTermIndex, rightCount)
let oExpression .= operator . " " . ReplaceIndex(a:iExpression, a:iIndex, HandleDecrement(lastTermIndex, rightCount),1)
let rightCount -= 1
endwhile
let oExpression .= operator . " " . ReplaceIndex(a:iExpression, a:iIndex, lastTermIndex,0)
echo oExpression
endfunc
func ReplaceIndex(iExpression, iIndex, iReplacement, iInsertBraces)
"the game we play here is to search for iIndex in such form that it is not part of any other string
"We should expect this to be the case if the character to the left or right of the index is not in [A-z] (or just to the right if a greek char)
let oExpression = ""
let strEndPosition = strlen(a:iExpression) - 1
let currPosition = 0
let indexLen = strlen(a:iIndex)
while currPosition <= strEndPosition
let indexCounter = 0
let foundIndex = 1
while indexCounter < indexLen
if a:iExpression[currPosition + indexCounter] == a:iIndex[indexCounter]
if a:iExpression[currPosition + indexLen] =~ '[a-zA-Z]'
let foundIndex = 0
let indexCounter = indexLen
elseif a:iExpression[currPosition -1] =~ '[a-zA-Z]' && a:iExpression[currPosition] != "\\"
let foundIndex = 0
let indexCounter = indexLen
else
let indexCounter+=1
endif
else
let indexCounter = indexLen
let foundIndex = 0
endif
endwhile
if foundIndex == 0
let oExpression .= a:iExpression[currPosition]
let currPosition+=1
else
if a:iInsertBraces == 1
let oExpression .= "{" . a:iReplacement . "}"
else
let oExpression .= a:iReplacement
endif
let currPosition+=indexLen
endif
endwhile
echo "oExpression: " . oExpression
return oExpression
endfunc
func HandleIncrement(iExpression, iIncrement)
"and what about negative numbers for iExpression!??? not handling these yet :[
let oExpression = ""
if !(a:iExpression[0] =~ '[0-9]') || a:iExpression < 10 && strlen(a:iExpression) > 1
let oExpression = a:iExpression . " + " . a:iIncrement
else
let oExpression = a:iExpression + a:iIncrement
endif
echo oExpression
return oExpression
endfunc
func HandleDecrement(iExpression, iIncrement)
"TODO and what about negative numbers for iExpression!??? not handling these yet :[
let oExpression = ""
if !(a:iExpression[0] =~ '[0-9]') || a:iExpression < 10 && strlen(a:iExpression) > 1
let oExpression = a:iExpression . " - " . a:iIncrement
else
let oExpression = a:iExpression - a:iIncrement
endif
echo oExpression
return oExpression
endfunc
func Interrogate(iQuestion)
call inputsave()
let answer = input(a:iQuestion)
call inputrestore()
return answer
endfunc
func InterrogateNumber(iQuestion)
call inputsave()
let answer = input(a:iQuestion)
call inputrestore()
"TODO what if negative number??
if !(answer[0] =~ '[0-9]')
let answer = InterrogateNumber(a:iQuestion . " you didn't enter a numerical value ")
endif
return answer
endfunc
As regards the mapping bit, I know it looks like I haven't done too much work but assuming I have lots more digging ahead of me to find the answer myself, can anyone help?
Update. Ok, I have something that works in a clumsy sort of way, i.e. if I define the following helperfunction:
func SumOrSequenceHelper()
let oIndex = Interrogate("index variable? ")
"go to last thing visually selected (I think!), yank it (putting it in the " register), then fetch it via oParam. Then pass this off to SumOrSequence
execute "normal! gvy"
let oExpression = getreg('"')
call SumOrSequence(oExpression, oIndex)
endfunc
vnoremap <F6> :call SumOrSequenceHelper()
then all is well, and I can just do an execute command to replace what I selected with what I got from SumOrSequence(...)
Would be grateful for any improvements but for all intents and purposes this one is solved :]

Answer 1

You could use a helper function like this:
func! GetSelectedText()
normal gv"xy
let result = getreg("x")
normal gv
return result
endfunc
vnoremap <F6> :call MyFunc(GetSelectedText())<cr>
There is also :com -range, which can register a custom command that operates on a selection, but the interface is line oriented.

Answer 2

Use the selection register to call the function with whatever you have visually selected.
vnoremap <F6> :call Test(#*)<CR>
If you just want to grab hold of the word under the cursor in Normal mode you can use this, which yanks to the selection register then uses the value. (You could yank to any named register instead , e.g. the a register with "ay and #a.)
noremap <S-F6> "*yaw:call Test(#*)<CR>
By the way these don't work with your Test function, but just calling it doesn't seem to work either?
:call Test("fred")
Error detected while processing function Test:
line 1:
E121: Undefined variable: a
E15: Invalid expression: a:iStr[0] =~ [a-zA-z]
They work with this test function:
function Test(iStr)
echo a:iStr
endfunction