Avoid throwing an error for frequent operations like completion

This patch introduces reduces inf-clojure-proc's responsabilities to only one:
return the processs. The new inf-clojure--proc-or-error will do both returning
and erroring.
This is necessary because while it is good to communicate an error on "eval"
operations, it is not good to have it on "under the hood" and very frequent
ones like completion and get arglists.

Author: arichiardi

inf-clojure.el

@@ -595,12 +595,12 @@ Prefix argument AND-GO means switch to the Clojure buffer afterwards."
   (let ((str (replace-regexp-in-string
               "[\n]+\\'" ""
               (buffer-substring-no-properties start end))))
-    (inf-clojure--send-string (inf-clojure-proc) str))
+    (inf-clojure--send-string (inf-clojure--proc-or-error) str))
   (when and-go (inf-clojure-switch-to-repl t)))
 
 (defun inf-clojure-eval-string (code)
   "Send the string CODE to the inferior Clojure process to be executed."
-  (inf-clojure--send-string (inf-clojure-proc) code))
+  (inf-clojure--send-string (inf-clojure--proc-or-error) code))
 
 (defun inf-clojure-eval-defun (&optional and-go)
   "Send the current defun to the inferior Clojure process.
@@ -691,7 +691,7 @@ The prefix argument SWITCH-TO-REPL controls whether to switch to REPL after the
     (comint-check-source file-name) ; Check to see if buffer needs saved.
     (setq inf-clojure-prev-l/c-dir/file (cons (file-name-directory    file-name)
                                               (file-name-nondirectory file-name)))
-    (inf-clojure--send-string (inf-clojure-proc)
+    (inf-clojure--send-string (inf-clojure--proc-or-error)
                               (format (inf-clojure-load-form) file-name))
     (when switch-to-repl
       (inf-clojure-switch-to-repl t))))
@@ -995,7 +995,7 @@ If you are using REPL types, it will pickup the most approapriate
 If you are using REPL types, it will pickup the most approapriate
 `inf-clojure-macroexpand-1-form` variant."
   (inf-clojure--sanitize-command
-   (pcase (inf-clojure--set-repl-type (inf-clojure-proc))
+   (pcase (inf-clojure--set-repl-type (inf-clojure--proc-or-error))
      (`planck inf-clojure-macroexpand-1-form-planck)
      (_ inf-clojure-macroexpand-1-form))))
 
@@ -1042,7 +1042,7 @@ prefix argument PROMPT-FOR-SYMBOL, it prompts for a symbol name."
   (let ((var (if prompt-for-symbol
                  (car (inf-clojure-symprompt "Var doc" (inf-clojure-symbol-at-point)))
                (inf-clojure-symbol-at-point))))
-    (inf-clojure--send-string (inf-clojure-proc) (format (inf-clojure-var-doc-form) var))))
+    (inf-clojure--send-string (inf-clojure--proc-or-error) (format (inf-clojure-var-doc-form) var))))
 
 (defun inf-clojure-show-var-source (prompt-for-symbol)
   "Send a command to the inferior Clojure to give source for VAR.
@@ -1052,7 +1052,7 @@ prefix argument PROMPT-FOR-SYMBOL, it prompts for a symbol name."
   (let ((var (if prompt-for-symbol
                  (car (inf-clojure-symprompt "Var source" (inf-clojure-symbol-at-point)))
                (inf-clojure-symbol-at-point))))
-    (inf-clojure--send-string (inf-clojure-proc) (format (inf-clojure-var-source-form) var))))
+    (inf-clojure--send-string (inf-clojure--proc-or-error) (format (inf-clojure-var-source-form) var))))
 
 ;;;; Response parsing
 ;;;; ================
@@ -1182,10 +1182,11 @@ for evaluation, therefore FORM should not include it."
 (defun inf-clojure-arglists (fn)
   "Send a query to the inferior Clojure for the arglists for function FN.
 See variable `inf-clojure-arglists-form'."
-  (thread-first
-      (format (inf-clojure-arglists-form) fn)
-    (inf-clojure--process-response (inf-clojure-proc) "(" ")")
-    (inf-clojure--some)))
+  (when-let ((proc (inf-clojure-proc)))
+    (thread-first
+        (format (inf-clojure-arglists-form) fn)
+      (inf-clojure--process-response proc "(" ")")
+      (inf-clojure--some))))
 
 (defun inf-clojure-show-arglists (prompt-for-symbol)
   "Show the arglists for function FN in the mini-buffer.
@@ -1207,7 +1208,7 @@ prefix argument PROMPT-FOR-NS, it prompts for a namespace name."
   (let ((ns (if prompt-for-ns
                 (car (inf-clojure-symprompt "Ns vars" (clojure-find-ns)))
               (clojure-find-ns))))
-    (inf-clojure--send-string (inf-clojure-proc) (format (inf-clojure-ns-vars-form) ns))))
+    (inf-clojure--send-string (inf-clojure-proc--or-error) (format (inf-clojure-ns-vars-form) ns))))
 
 (defun inf-clojure-set-ns (prompt-for-ns)
   "Set the ns of the inferior Clojure process to NS.
@@ -1220,13 +1221,13 @@ PROMPT-FOR-NS, it prompts for a namespace name."
               (clojure-find-ns))))
     (when (or (not ns) (equal ns ""))
       (user-error "No namespace selected"))
-    (inf-clojure--send-string (inf-clojure-proc) (format (inf-clojure-set-ns-form) ns))))
+    (inf-clojure--send-string (inf-clojure-proc--or-error) (format (inf-clojure-set-ns-form) ns))))
 
 (defun inf-clojure-apropos (var)
   "Send a form to the inferior Clojure to give apropos for VAR.
 See variable `inf-clojure-apropos-form'."
   (interactive (inf-clojure-symprompt "Var apropos" (inf-clojure-symbol-at-point)))
-  (inf-clojure--send-string (inf-clojure-proc) (format (inf-clojure-apropos-form) var)))
+  (inf-clojure--send-string (inf-clojure--proc-or-error) (format (inf-clojure-apropos-form) var)))
 
 (defun inf-clojure-macroexpand (&optional macro-1)
   "Send a form to the inferior Clojure to give apropos for VAR.
@@ -1235,21 +1236,23 @@ With a prefix arg MACRO-1 uses `inf-clojure-macroexpand-1-form'."
   (interactive "P")
   (let ((last-sexp (buffer-substring-no-properties (save-excursion (backward-sexp) (point)) (point))))
     (inf-clojure--send-string
-     (inf-clojure-proc)
+     (inf-clojure--proc-or-error)
      (format (if macro-1
                  (inf-clojure-macroexpand-1-form)
                (inf-clojure-macroexpand-form))
              last-sexp))))
 
-
 (defun inf-clojure-proc ()
   "Return the current inferior Clojure process.
 See variable `inf-clojure-buffer'."
-  (let ((proc (get-buffer-process (if (derived-mode-p 'inf-clojure-mode)
-                                      (current-buffer)
-                                    inf-clojure-buffer))))
-    (or proc
-        (error "No Clojure subprocess; see variable `inf-clojure-buffer'"))))
+  (get-buffer-process (if (derived-mode-p 'inf-clojure-mode)
+                          (current-buffer)
+                        inf-clojure-buffer)))
+
+(defun inf-clojure--proc-or-error ()
+  "Return the current inferior Clojure process.
+See variable `inf-clojure-buffer'."
+  (or (inf-clojure-proc) (error "No Clojure subprocess; see variable `inf-clojure-buffer'")))
 
 (defun inf-clojure--list-or-nil (data)
   "Return DATA if and only if it is a list."
@@ -1271,11 +1274,11 @@ every other EXPR will be discarded and nil will be returned."
 Under the hood it calls the function
 \\[inf-clojure-completions-fn] passing in the result of
 evaluating \\[inf-clojure-completion-form] at the REPL."
-  (when (not (string-blank-p expr))
-    (let ((proc (inf-clojure-proc))
-          (completion-form (format (inf-clojure-completion-form) (substring-no-properties expr))))
-      (funcall inf-clojure-completions-fn
-               (inf-clojure--process-response completion-form proc  "(" ")")))))
+  (let ((proc (inf-clojure-proc)))
+    (when (and proc (not (string-blank-p expr)))
+      (let ((completion-form (format (inf-clojure-completion-form) (substring-no-properties expr))))
+        (funcall inf-clojure-completions-fn
+                 (inf-clojure--process-response completion-form proc  "(" ")"))))))
 
 (defcustom inf-clojure-completions-fn 'inf-clojure-list-completions
   "The function that parses completion results.