Add define/abstract/error.

scribblings/utils.scrbl

@@ -4,7 +4,8 @@
 	  	     "../utils.rkt"
 		     (only-in typed/graph Graph)
 		     (only-in racket/set set)
-		     (only-in racket/stream stream->list stream-take)))
+		     (only-in racket/stream stream->list stream-take)
+		     (only-in typed/racket/class class super-new new send)))
 
 @(define utils-evaluator
   (parameterize ([sandbox-output 'string]
@@ -88,6 +89,24 @@ The implementation of these macros is a simplified version the definition of
 
 }
 
+@defform[(define/abstract/error method-name args ...)]{
+
+In a typed class, defines a public method @racket[method-name] with the
+arguments @racket[args] and with the body announcing that this method
+is abstract.
+
+@ex[
+(define my-abstract-class%
+  (class object%
+    (super-new)
+
+    (: abstract-increment (-> Integer Integer))
+    (define/abstract/error (abstract-increment x))))
+
+(define obj (new my-abstract-class%))
+(eval:error (send obj abstract-increment 1))
+]}
+
 @section{Hashtable injection}
 
 This section defines some utilities to streamline the usage of hash tables

utils.rkt

@@ -6,7 +6,7 @@
 (provide
  Variable VariableMapping GeneralPair
 
- assert-type for/first/typed for*/first/typed
+ assert-type for/first/typed for*/first/typed define/abstract/error
  eval-with eval1-with auto-hash-ref/explicit auto-hash-ref/:
  extract-symbols any->string stringify-variable-mapping string->any
  handle-org-booleans map-sexp read-org-sexp unorg unstringify-pairs
@@ -61,6 +61,10 @@
                     (cons i j))
                   '(2 . 4))))
 
+(define-syntax-parser define/abstract/error
+  [(_ (name:id args:id ...))
+   #`(define/public (name args ...) (error 'name "abstract method"))])
+
 (: eval-with (-> (VariableMapping Any) Any AnyValues))
 (define (eval-with ht expr)
   (parameterize ([current-namespace (make-base-namespace)])