+(define-syntax-rule (modify-phases phases mod-spec ...)
+ "Modify PHASES sequentially as per each MOD-SPEC, which may have one of the
+following forms:
+
+ (delete <old-phase-name>)
+ (replace <old-phase-name> <new-phase>)
+ (add-before <old-phase-name> <new-phase-name> <new-phase>)
+ (add-after <old-phase-name> <new-phase-name> <new-phase>)
+
+Where every <*-phase-name> is an automatically quoted symbol, and <new-phase>
+an expression evaluating to a procedure."
+ (let* ((phases* phases)
+ (phases* (%modify-phases phases* mod-spec))
+ ...)
+ phases*))
+
+(define-syntax %modify-phases
+ (syntax-rules (delete replace add-before add-after)
+ ((_ phases (delete old-phase-name))
+ (alist-delete 'old-phase-name phases))
+ ((_ phases (replace old-phase-name new-phase))
+ (alist-replace 'old-phase-name new-phase phases))
+ ((_ phases (add-before old-phase-name new-phase-name new-phase))
+ (alist-cons-before 'old-phase-name 'new-phase-name new-phase phases))
+ ((_ phases (add-after old-phase-name new-phase-name new-phase))
+ (alist-cons-after 'old-phase-name 'new-phase-name new-phase phases))))
+