grokking simplicity and refactoring

packages/lab-tool/utils/ssh/retry.scm

@@ -0,0 +1,45 @@
+;; utils/ssh/retry.scm - Pure retry logic
+
+(define-module (utils ssh retry)
+  #:use-module (utils logging)
+  #:use-module (utils ssh remote-command)
+  #:export (with-retry
+            run-command-with-retry))
+
+;; Pure function: Retry operation with exponential backoff
+;; Input: operation (thunk), max-retries number, delay-fn (retry-count -> seconds)
+;; Output: result of operation or #f if all retries failed
+(define (with-retry operation max-retries . delay-fn)
+  "Pure retry logic - operation should return (values success? result)"
+  (let ((delay-func (if (null? delay-fn) 
+                        (lambda (retry) (* retry 2))  ; Default: exponential backoff
+                        (car delay-fn))))
+    (let loop ((retries 0))
+      (call-with-values operation
+        (lambda (success result)
+          (if success
+              (values #t result)
+              (if (< retries max-retries)
+                  (begin
+                    (sleep (delay-func retries))
+                    (loop (+ retries 1)))
+                  (values #f result))))))))
+
+;; Impure wrapper: Run command with retry and logging
+(define (run-command-with-retry machine-name command max-retries . args)
+  "Run command with retry logic (with side effects: logging)"
+  (let ((operation (lambda ()
+                     (apply run-remote-command machine-name command args))))
+    (let loop ((retries 0))
+      (call-with-values operation
+        (lambda (success output)
+          (if success
+              (values #t output)
+              (if (< retries max-retries)
+                  (begin
+                    (log-warn "Command failed, retrying (~a/~a)..." (+ retries 1) max-retries)
+                    (sleep 2)
+                    (loop (+ retries 1)))
+                  (begin
+                    (log-error "Command failed after ~a retries" max-retries)
+                    (values #f output))))))))))