zsh(racket): manage Racket paths with symlinks

Use `zuo . symlink-racket-paths` to update the symlinks to the correct
paths, and then (as ~/.zsh/paths.zsh) make sure those paths are on the
right PATH variables. This eliminates a lot of pathrm/pathadd when new
Rackets are released.

Ref: https://racket.discourse.group/t/is-there-a-better-way-to-manage-getting-the-right-user-console-bin-dir-on-path-for-running-shells-when-upgrading-racket/3203/2

links/zsh/mac/paths.zsh

@@ -14,14 +14,3 @@
   pathadd_front /usr/local/opt/openjdk/bin
   pathadd_front man /usr/local/opt/openjdk/libexec/openjdk.jdk/Contents/Home/man
 }
-
-command -v racket &>/dev/null && {
-  racket_paths=($(IFS=$'\n' racket -I racket/base -e '
-    (require setup/dirs)
-    (for-each displayln
-      (list (find-user-console-bin-dir)
-            (find-user-man-dir)))
-  '))
-  pathadd $racket_paths[1]
-  pathadd man $racket_paths[2]
-}

links/zsh/paths.zsh

@@ -0,0 +1,2 @@
+pathadd ~/.racket-bin
+pathadd man ~/.racket-man

main.zuo

@@ -138,7 +138,29 @@
                      (rm* dest)
                      (symlink src #;<- dest)
                      (alert (~a dest " -> " src)))
-                   (hash-keys the-links)))]))
+                   (hash-keys the-links)))]
+      [:target symlink-racket-paths ()
+               ,(lambda (token)
+                  (define paths
+                    (car
+                     (string-read
+                      (shell/output `("racket -I racket/base -e"
+                                      ,(string->shell
+                                        (string-join
+                                         '("(require setup/dirs)"
+                                           "(write (map path->bytes"
+                                           "            (list (find-user-console-bin-dir)"
+                                           "                  (find-user-man-dir))))")))))
+                      0
+                      "$(racket -I racket/base -e ...)")))
+                  (define bin-dir (car paths))
+                  (define man-dir (cadr paths))
+                  (define racket-bin (at-home ".racket-bin"))
+                  (define racket-man (at-home ".racket-man"))
+                  (symlink bin-dir #;<- racket-bin)
+                  (alert (~a racket-bin " -> " bin-dir))
+                  (symlink man-dir #;<- racket-man)
+                  (alert (~a racket-man " -> " man-dir)))]))
 
   (make-targets targets))