diff --git a/src/core.bjo b/src/core.bjo
index 33bc35c..1d6198f 100644
--- a/src/core.bjo
+++ b/src/core.bjo
@@ -156,31 +156,33 @@
 ;; ---------------------------------------------------------------------------
 
 ;; VS Code's themes, the ones TextMateSharp carries: #:theme 'dark-plus.
-(type (: TmTheme (Union (: ThemeDarkPlus #:tag dark-plus)
-                        (: ThemeLightPlus #:tag light-plus)
-                        (: ThemeDark #:tag dark)
-                        (: ThemeLight #:tag light)
-                        (: ThemeMonokai #:tag monokai)
-                        (: ThemeDimmedMonokai #:tag dimmed-monokai)
-                        (: ThemeOneDark #:tag one-dark)
-                        (: ThemeAtomOneDark #:tag atom-one-dark)
-                        (: ThemeAtomOneLight #:tag atom-one-light)
-                        (: ThemeDracula #:tag dracula)
-                        (: ThemeSolarizedDark #:tag solarized-dark)
-                        (: ThemeSolarizedLight #:tag solarized-light)
-                        (: ThemeQuietLight #:tag quiet-light)
-                        (: ThemeKimbieDark #:tag kimbie-dark)
-                        (: ThemeTomorrowNightBlue #:tag tomorrow-night-blue)
-                        (: ThemeAbyss #:tag abyss)
-                        (: ThemeRed #:tag red)
-                        (: ThemeHighContrastDark #:tag high-contrast-dark)
-                        (: ThemeHighContrastLight #:tag high-contrast-light)
-                        (: ThemeVisualStudioDark #:tag visual-studio-dark)
-                        (: ThemeVisualStudioLight #:tag visual-studio-light))))
+(def/grammar TmTheme
+  (:or (: ThemeDarkPlus 'dark-plus)
+       (: ThemeLightPlus 'light-plus)
+       (: ThemeDark 'dark)
+       (: ThemeLight 'light)
+       (: ThemeMonokai 'monokai)
+       (: ThemeDimmedMonokai 'dimmed-monokai)
+       (: ThemeOneDark 'one-dark)
+       (: ThemeAtomOneDark 'atom-one-dark)
+       (: ThemeAtomOneLight 'atom-one-light)
+       (: ThemeDracula 'dracula)
+       (: ThemeSolarizedDark 'solarized-dark)
+       (: ThemeSolarizedLight 'solarized-light)
+       (: ThemeQuietLight 'quiet-light)
+       (: ThemeKimbieDark 'kimbie-dark)
+       (: ThemeTomorrowNightBlue 'tomorrow-night-blue)
+       (: ThemeAbyss 'abyss)
+       (: ThemeRed 'red)
+       (: ThemeHighContrastDark 'high-contrast-dark)
+       (: ThemeHighContrastLight 'high-contrast-light)
+       (: ThemeVisualStudioDark 'visual-studio-dark)
+       (: ThemeVisualStudioLight 'visual-studio-light)))
 
 ;; How a node is coloured: #:style 'inline or #:style 'classes.
-(type (: TmStyleMode (Union (: StyleInline #:tag inline)
-                            (: StyleClasses #:tag classes))))
+(def/grammar TmStyleMode
+  (:or (: StyleInline 'inline)
+       (: StyleClasses 'classes)))
 
 ;; How a piece of text looks. None is the theme's own colour, which the pre
 ;; around the code already has.