An Emacs configuration to colour Haskell code blocks in lhs2tex

lhs2tex-mode.el

;; I wrote a bit of Emacs configuration (which can be added to your
;; init.el) so that an lhs2tex file can be syntax-highlighted as a
;; Latex file but the Haskell code is highlighted as Haskell code. In
;; fact it's a little more than this, as the code blocks are
;; interpreted with the haskell-mode, so you can use your haskell
;; commands there.
;;
;; I don't recommend opening all `.lhs' file in this mode, as they
;; don't need to be Latex files. Literate Haskell is really agnostic
;; about its surrounding language.
;;
;; Instead I add the following code snippet in the .dir-locals.el of
;; repos where I do lhs2tex stuff.
;;
;;   ((nil . ((eval . (add-hook 'hack-local-variables-hook
;;                              (lambda () (when (derived-mode-p 'latex-mode)
;;                                           (poly-latex-lhs-mode))))))))

(use-package polymode
  :ensure t)

(define-innermode aspiwack/poly-latex-haskell-innermode
  :mode 'haskell-mode
  :head-matcher "^[ \t]*\\\\begin{\\(code\\|spec\\)}"
  :tail-matcher "^[ \t]*\\\\end{\\(code\\|spec\\)}"
  :head-mode 'host
  :tail-mode 'host)

(define-polymode poly-latex-lhs-mode poly-latex-root-polymode
  :innermodes '(aspiwack/poly-latex-haskell-innermode))