tiny refac

brag/codegen/runtime.rkt

@@ -174,34 +174,38 @@ This would be the place to check a syntax property for hiding.
 (define (remove-rule-name component-stx #:splice? [splice #f])
   ;; when removing a rule name, we apply it as a syntax property to the remaining elements
   ;; for possible later usage (aka, why throw away information)   
-  (with-syntax ([(name . subcomponents) component-stx])
-    (let ([name-datum (syntax->datum #'name)])
-      (if splice
-          ;; when splicing, returned list is a regular list, with each element having the property.
-          (map (λ(sc) (syntax-property sc name-datum #'name)) (syntax->list #'subcomponents))
-          ;; when hiding, returned list should be a syntaxed list with the property
-          ;; iow, basically the same as `component-stx`, minus the name
-          (syntax-property (datum->syntax component-stx #'subcomponents component-stx component-stx) name-datum #'name)))))
-
-
-(define (preprocess-component-lists component-lists)
+  (syntax-case component-stx ()
+    [(name . subcomponents)
+     (let ([name-datum (syntax->datum #'name)])
+       (if splice
+           ;; when splicing, returned list is a regular list, with each element having the property.
+           (map (λ(sc) (syntax-property sc name-datum #'name)) (syntax->list #'subcomponents))
+           ;; when hiding, returned list should be a syntaxed list with the property
+           ;; iow, basically the same as `component-stx`, minus the name
+           (syntax-property (datum->syntax component-stx #'subcomponents component-stx component-stx) name-datum #'name)))]
+    [_ (raise-syntax-error 'remove-rule-name "component has no name" component-stx)]))
+
+
+(define (preprocess-component component-stx)
+  (cond
+    ;; test splice first in case both hiding and splicing are set, for instance:
+    ;; /rule : thing @rule
+    ;; otherwise the hide prevents the splice from being expressed
+    [(or (eq? (syntax-property component-stx 'hide-or-splice) 'splice)
+         (syntax-property component-stx 'splice-rh-id))
+     (remove-rule-name component-stx #:splice? #t)] ; spliced version is lifted out of the sublist
+    [(eq? (syntax-property component-stx 'hide-or-splice) 'hide)
+     (list (remove-rule-name component-stx))] ; hidden version still wrapped in a sublist
+    [else (list component-stx)]))
+
+
+(define (preprocess-component-lists component-stxss)
   ; "preprocess" means splicing and rule-name-hiding where indicated
+  ;; inside `component-stx` is a rule name followed by subcomponents
   (append*
-   ;; each `component-list` is a list that's either empty, or has a single component-stx object
-   ;; inside `component-stx` is a name followed by subcomponents
-   (for*/list ([component-list (in-list component-lists)]
-               [component-stx (in-list component-list)]) ; this has the effect of omitting any empty `component-list`
-     (list
-      (cond
-        ;; test splice first in case both hiding and splicing are set, for instance:
-        ;; /rule : thing @rule
-        ;; otherwise the hide prevents the splice from being expressed
-        [(or (eq? (syntax-property component-stx 'hide-or-splice) 'splice)
-             (syntax-property component-stx 'splice-rh-id))
-         (remove-rule-name component-stx #:splice? #t)] ; spliced version is lifted out of the sublist
-        [(eq? (syntax-property component-stx 'hide-or-splice) 'hide)
-         (list (remove-rule-name component-stx))] ; hidden version still wrapped in a sublist
-        [else (list component-stx)])))))
+   (for*/list ([component-stxs (in-list component-stxss)]
+               [component-stx (in-list component-stxs)])
+              (preprocess-component component-stx))))
 
 
 ;; rule-components->syntax: (U symbol false) (listof stx) ... #:srcloc (U #f (list src line column offset span)) -> stx
@@ -209,7 +213,7 @@ This would be the place to check a syntax property for hiding.
 ;; The location information of the rule spans that of its components.
 (define (rule-components->syntax rule-name/false #:srcloc [srcloc #f] #:hide-or-splice? [hide-or-splice #f] . component-lists)
   (define new-rule-name (datum->syntax #f rule-name/false srcloc stx-with-original?-property))
-  (define new-rule-components (append* (preprocess-component-lists component-lists)))
+  (define new-rule-components (preprocess-component-lists component-lists))
   (define rule-result (cons new-rule-name new-rule-components))
   (define syntaxed-rule-result (datum->syntax #f rule-result srcloc stx-with-original?-property))
   ;; not 'hide-or-splice-lhs-id, because this will now become a (right-hand) component in a different (left-hand) rule