How to define a yasnippet whose content depends on the value of an Elisp variable?

Question

I want to define a yasnippet for shell-script mode that would insert a chunk of text whose content depends on the setting of the sh-shell variable.

Since the possible different text insertions are several lines long, and are quite different from each other, so doing this with conditional fields of the form

${N:`(case sh-shell (zsh  "foo")
                    (bash "bar")
                    (sh   "baz")
                    (t    "frobozz"))`}

...would all but eliminate the convenient formatting one this sort of template for.

EDIT: To clarify: the code above is not useful to me, because I need to insert multi-line formatted text, not little, one-word strings like "foo", "bar", etc.

---

If I were to use an unholy mix of Elisp and bash to represent what I'm looking for, this is how I'd represent it:

`(case sh-shell (zsh <<EOZSH)
zsh version
    of
    snippet
    looks
    like
    this
EOZSH
                   (bash <<EOBASH)
bash version of snippet looks like this
EOZSH
                   (sh   <<EOSH)
sh
 version
  of
   snippet
    looks
     like
      this
EOSH
                   (t    <<EODEFAULT)
default version
  of snippet
    looks
    like
    this
EOSH
)`

IOW, the snippet would consist of a single embedded Elisp case expression, where the key of each key-value pair is a possible value of sh-shell, and the value is a (formatted) snippet/template; I've represented the latter using (totally invalid) heredoc notation.

---

Is there a (syntactically sound) way to implement this idea?

Answer 1

You can call any elisp function from your snippet definition, so if you can use a helper function defined in your init file to keep the snippet file tidier. In your .emacs or .emacs.d/init.el:

(defun snippet-helper ()
  (cond ((string-equal sh-shell "zsh") "foo")
        ((string-equal sh-shell "bash") "bar")
        ((string-equal sh-shell "sh") "baz")
        (t "foo")))

(note that the case form doesn't work when comparing strings that aren't the same object, so I used cond instead).

Then your snippet becomes:

# -*- mode: snippet -*-
# name: hhh
# key: hhh
# --
${N:`(snippet-helper)`}