VS Code if/else conditions with regular expression in user defined snippet - regex

Question

I am pretty bad at regex and need some help implementing my idea with the already complicated if-else syntax being used for user-defined snippets in VS Code.
I want to achieve the following:
Whenever I enter a number for variable $1 I want the snippet to create the
text "MAXVALUE $1" at the placeholder positon
if anything else is entered, there should be printed nothing
My current line for this with $1 being the variable I enter is:
"\t ${1/([0-9])|([a-zA-Z])/${1:+MAXVALUE }${2:+ }/}"
At this state I can capture the entire number EXCEPT the FRIST CHARACTER being entered and I can print MAXVALUE _mynumber_minus_char_at_index_0, LOL?!
If I enter a text, MAXVALUE won't be printed, but again the value from $1 minus the character at index 0 is being printed on screen.
Any help would be highly appreciated. If you got some useful links that explain advanced snippet creation for those kinda cases, I would be thankful as well.
For RegEx, well, time to learn them, so why not starting with a crazy-ass example like this - at least for me it is like rocket-science atm :D
Thanks in advance and best regards.

Answer 1

Using this snippet:
"Maxvalue": {
"prefix": "cll",
"body": [
"\t ${1/([0-9]+)|([a-zA-Z]+)/${1:+MAXVALUE }$1${2:+ }/}",
],
"description": "maxvalue"
},
([0-9]+) captures all the numbers you type; or
([a-zA-Z]+) captures all the letters you type
You were using ([0-9]) which captures, but more importantly
matches only the first number. If you don't match something it will not be transformed by the snippet transform, it just remains
untouched. That is why you were seeing everything but the first
number in the output.
You weren't actually outputting $1 anywhere - you see I added it to the transform after the MAXVALUE conditional.
${1:+MAXVALUE } is a conditional which means if there is a capture group 1, do something, in this case output MAXVALUE. That 1 in ${1:+MAXVALUE } is not a reference to your $1 tabstop. It is only a reference to the first capture group of your regex.
So you correctly outputted MAXVALUE when you had a capture group 1, but you didn't follow that up by outputting capture group 1 anywhere.
{2:+ } is anther conditional where the 2 refers to a capture group 2, if any, here ([a-zA-Z]+). So if there is a capture group 2, a space will be output. If there is no capture group 2, the conditional will fail and provide no output of its own. If you want nothing printed if you type letters, then match it and do nothing with it. As in the following:
"\t ${1/([0-9]+)|[a-zA-Z]+/${1:+MAXVALUE }$1/}", this will match all the letters you type (before tabbing to complete the transform) and they will disappear because you matched them and then didn't output them in the transform part anywhere.
If you simply want those letters to remain, don't match them as in
"\t ${1/([0-9]+)/${1:+MAXVALUE }$1/}"
If there is something you don't understand let me know.
[By the way, your question title mentions if/else conditions but you are using only if conditionals.]