Mirror with character replacement in yasnippet

Question

I would like to do 2 things: first mirror a field and replace spaces with "-". If nothing is typed in the field, junto to the mirror. The code is:

 \begin{theorem}[$1]
 \label{thm-${1:$( ???? )}}
 $0
 \end{theorem}

Answer 1

I'm not sure I fully understand the question, this will mirror your first field replacing spaces with - character:

# -*- mode: snippet -*-
# name: theorem
# key: theorem
# --
\begin\{theorem\}[$1]
\label\{thm-${1:$(replace-regexp-in-string "[[:space:]]" "-" yas-text)}\}
$0
\end\{theorem\}

P.S. I would also downcase the whole thing, just because it looks better, but to do this you would need to define auxiliary function in your config or this may get cumbersome.

Answer 2

Here is how I ended up doing. We can define a function as below and load it in emacs.

(defun string-for-latex-labels (string)
  "format automatic labels for latex environment to use with snippet"
  (setq string  (replace-regexp-in-string "[[:punct:]]" "-" string))
  (setq string  (replace-regexp-in-string "[[:space:]]" "-" string))
  (setq string  (replace-regexp-in-string "-+" "-" string))
  (setq string  (replace-regexp-in-string "^-" "" string))
  (setq string  (replace-regexp-in-string "-$" "" string))
  (setq string  (downcase string))
 )

Then we can just define a snippet as

# -*- mode: snippet -*-
# name: theorem
# key: theorem
# --
\begin\{theorem\}[$1]
\label{thm-${2:${1:$(string-for-latex-labels yas-text)}}}
$0
\end\{theorem\}