Add doc-of function to core for reverse documentation lookup.

CHANGELOG.md

@@ -2,6 +2,7 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased - ???
+- Add `doc-of` for reverse documentation lookup.
 - Add `ev/gather` and `chan` argument to `ev/go`. This new argument allows "supervisor channels"
   for fibers to enable structured concurrency.
 - Make `-k` flag work on stdin if no files are given.

src/boot/boot.janet

@@ -2018,20 +2018,8 @@
   (print (doc-format (string "Dynamics:\n\n" (string/join dynamics " "))))
   (print "\n    Use (doc sym) for more information on a binding.\n"))
 
-(defn doc*
-  "Get the documentation for a symbol in a given environment. Function form of doc."
-  [&opt sym]
-
-  (cond
-    (string? sym)
-    (print-index (fn [x] (string/find sym x)))
-
-    sym
-    (do
-      (def x (dyn sym))
-      (if (not x)
-        (print "symbol " sym " not found.")
-        (do
+(defn- print-module-entry
+  [x]
   (def bind-type
     (string "    "
             (cond
@@ -2047,7 +2035,26 @@
            (string "    " path " on line " line ", column " col "\n") "")
          (if (or d sm) "\n" "")
          (if d (doc-format d) "    no documentation found.")
-                 "\n\n"))))
+         "\n\n"))
+
+(def module/cache
+  "Table mapping loaded module identifiers to their environments."
+  @{})
+
+(defn doc*
+  "Get the documentation for a symbol in a given environment. Function form of doc."
+  [&opt sym]
+
+  (cond
+    (string? sym)
+    (print-index (fn [x] (string/find sym x)))
+
+    sym
+    (do
+      (def x (dyn sym))
+      (if (not x)
+        (print "symbol " sym " not found.")
+        (print-module-entry x)))
 
     # else
     (print-index identity)))
@@ -2060,8 +2067,25 @@
   [&opt sym]
   ~(,doc* ',sym))
 
+(defn doc-of
+  `Searches all loaded modules in module/cache for a given binding and prints out its documentation.
+  This does a search by value instead of by name. Returns nil.`
+  [x]
+  (var found false)
+  (loop [module-set :in [[root-env] module/cache]
+         module :in module-set
+         value :in module]
+    (let [check (or (get value :ref) (get value :value))]
+      (when (= check x)
+        (print-module-entry value)
+        (set found true)
+        (break))))
+  (if-not found
+    (print "documentation for value " x " not found.")))
+
 (undef env-walk)
 (undef print-index)
+(undef print-module-entry)
 
 ###
 ###
@@ -2644,10 +2668,6 @@
 (setdyn :syspath (boot/opts "JANET_PATH"))
 (setdyn :headerpath (boot/opts "JANET_HEADERPATH"))
 
-(def module/cache
-  "Table mapping loaded module identifiers to their environments."
-  @{})
-
 (defn module/add-paths
   ```
   Add paths to module/paths for a given loader such that