std/misc/rtd: add type=?

mighty-gerbils · Nov 3, 2023 · 027572e · 027572e
1 parent d4794cc
commit 027572e
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diff --git a/doc/reference/std/misc/rtd.md b/doc/reference/std/misc/rtd.md
@@ -71,6 +71,34 @@ type object.
 ```
 :::
 
+## type=?
+``` scheme
+(type=? typ1 type2) -> bool
+
+  typ1 := type object
+  typ2 := other type object
+```
+
+Returns true if the two type objects have the same `type-id`.
+This is the preferred equality predicate for types.
+`eq?` and `eqv?` should also work, but at present
+`equal?` seems to be broken.
+
+::: tip Examples:
+``` scheme
+> (defstruct a ())
+> (defclass  b ())
+> (type-id a::t)
+#:a::t45
+> (type-id b::t)
+#:b::t49
+> (type=? a::t a::t)
+#t
+> (type=? a::t b::t)
+#f
+```
+:::
+
 ## type-name
 ``` scheme
 (type-name typ) -> type name | error

diff --git a/src/std/misc/rtd.ss b/src/std/misc/rtd.ss
@@ -3,7 +3,7 @@
 ;;; safe type descriptor accessors
 (import :std/error)
 (export (rename: checked-object-type object-type)
-        type? type-id type-name type-super
+        type? type=? type-id type-name type-super
         type-descriptor?
         (rename: checked-type-descriptor-mixin type-descriptor-mixin)
         (rename: checked-type-descriptor-fields type-descriptor-fields)
@@ -52,3 +52,6 @@
 (defcheck-type-descriptor checked-type-descriptor-ctor type-descriptor-ctor)
 (defcheck-type-descriptor checked-type-descriptor-slots type-descriptor-slots)
 (defcheck-type-descriptor checked-type-descriptor-methods type-descriptor-methods)
+
+(def (type=? x y)
+  (eq? (type-id x) (type-id y)))