Made it possible to use (refresh-makefile) in order to refresh an edited makefile on the fly.

main.rkt

@@ -15,6 +15,7 @@
          phony
          default-target
          make
+         refresh-makefile
          run
          raco
          rm-f
@@ -29,6 +30,47 @@
          )
          ;(all-from-out git))
 
+
+;; The makefile module currently loaded in this Racket process.  Keeping only
+;; its source path is enough: target state lives in the engine and is rebuilt
+;; when the makefile module is evaluated again.
+(define loaded-makefile #f)
+
+(define (remember-makefile! path)
+  (set! loaded-makefile path)
+  (void))
+
+(define-for-syntax (remember-source-form stx)
+  (define source (syntax-source stx))
+  (if (path? source)
+      #`(remember-makefile! (string->path #,(path->string source)))
+      #'(void)))
+
+(define (refresh-makefile)
+  (unless loaded-makefile
+    (error 'refresh-makefile "no racket-makefile has been loaded"))
+  (define source loaded-makefile)
+  (define directory (or (path-only source) (current-directory)))
+  ;; Load the edited makefile as a fresh module in the same namespace. Its
+  ;; required modules therefore reuse their existing module instances, while
+  ;; the makefile body itself runs again and re-registers all targets.
+  (define refresh-source
+    (make-temporary-file "racket-makefile-refresh~a.rkt" #f directory))
+  (copy-file source refresh-source #t)
+  ;; With #lang racket, main.rkt is only required and our custom module-begin
+  ;; does not run. Reset explicitly so removed/renamed targets disappear too.
+  (reset-makefile!)
+  (dynamic-wind
+    void
+    (lambda ()
+      (dynamic-require refresh-source #f))
+    (lambda ()
+      ;; Loading the temporary copy also runs remember-makefile!. Keep the
+      ;; original source as the file to use for the next refresh.
+      (set! loaded-makefile source)
+      (delete-file refresh-source)))
+  (void))
+
 ;; For target declarations we want a bound identifier to remain an ordinary
 ;; Racket expression. This makes generated targets such as (target obj ...)
 ;; possible inside a for loop. An unbound identifier is a literal target name.
@@ -51,10 +93,12 @@
     [(_ form ...)
      #'(racket-module-begin
         (reset-makefile!)
+        (remember-makefile!
+         (variable-reference->module-source (#%variable-reference)))
         form ...
         ;; Re-export make so that `racket -t Makefile.rkt -e "(make all)"`
         ;; imports the make form into the command-line evaluation namespace.
-        (provide make quote #%top-interaction #%app #%datum #%top))]))
+        (provide make refresh-makefile quote #%top-interaction #%app #%datum #%top))]))
 
 (define-syntax (deps stx)
   (raise-syntax-error 'deps "only valid as the dependency clause of target" stx))
@@ -66,30 +110,42 @@
                    [(target-dependency ...)
                     (map literal-name-or-expression
                          (syntax->list #'(dependency ...)))])
-       #'(register-target!
-          target-name
-          (list target-dependency ...)
-          (lambda () body ... (void))))]
+       (with-syntax ([remember-source (remember-source-form stx)])
+         #'(begin
+             remember-source
+             (register-target!
+              target-name
+              (list target-dependency ...)
+              (lambda () body ... (void))))))]
     [(_ name body ...)
-     (with-syntax ([target-name (literal-name-or-expression #'name)])
-       #'(register-target!
-          target-name
-          '()
-          (lambda () body ... (void))))]))
+     (with-syntax ([target-name (literal-name-or-expression #'name)]
+                   [remember-source (remember-source-form stx)])
+       #'(begin
+           remember-source
+           (register-target!
+            target-name
+            '()
+            (lambda () body ... (void)))))]))
 
 (define-syntax (phony stx)
   (syntax-case stx ()
     [(_ name ...)
      (with-syntax ([(target-name ...)
                     (map literal-name-or-expression
-                         (syntax->list #'(name ...)))])
-       #'(mark-phony! target-name ...))]))
+                         (syntax->list #'(name ...)))]
+                   [remember-source (remember-source-form stx)])
+       #'(begin
+           remember-source
+           (mark-phony! target-name ...)))]))
 
 (define-syntax (default-target stx)
   (syntax-case stx ()
     [(_ name)
-     (with-syntax ([target-name (literal-name-or-expression #'name)])
-       #'(set-default-target! target-name))]))
+     (with-syntax ([target-name (literal-name-or-expression #'name)]
+                   [remember-source (remember-source-form stx)])
+       #'(begin
+           remember-source
+           (set-default-target! target-name)))]))
 
 (define-syntax (make stx)
   (syntax-case stx ()