I've been considering adding lexical lookup to s-format

[nicferrier]

So you can do this:

(let ((x 1))
  (s-format "x is ${x}" 'lex-value))

Good idea? Bad idea?

[magnars]

I think that looks brilliant. But maybe as a separate function, so you can ditch the 'lex-value all together?

(let ((x 1))
  (s-lex-format "x is ${x}"))

[nicferrier]

The only trouble with that is that I think there are two things that
would be useful, lexical access and lexical access with Lisp output:

I'm using this code right now:

(defvar lexical-value-when-dynamic :error
  "How `lexical-value' should act in dynamic scope.

Valid values are `:error', which is the default and causes
`lexical-value' to error when called in dynamic scope, or
`:symbol-value' which causes the `symbol-value' function to be
called for the symbol or `nil' which causes nil to be returned.")

(defmacro lexical-value (lexical-symbol)
  "What is the value of the LEXICAL-SYMBOL specified?"
  (let ((pv (make-symbol "pv"))
        (sv (make-symbol "snv")))
    `(let ((,pv (lambda ())))
       (if (eq 'closure (car ,pv))
           (let ((value 
                  (assoc ,lexical-symbol (cadr ,pv))))
             (when value (cdr value)))
           (case lexical-value-when-dynamic
             (:error (error "not in a lexical environment"))
             (:symbol-value (symbol-value ,lexical-symbol))
             (t nil))))))

(defmacro with-sformat-lex (&rest body)
  (declare (debug (&rest form))
           (indent 0))
  `(flet ((lex-val (var)
            (let ((lexical-value-when-dynamic :symbol-value)
                  (variable (intern var)))
              (lexical-value variable)))
          (lisp-val (var) (format "%S" (lex-val var))))
     ,@body))

So I can go:

(let ((x 1)
      (y '(a b c)))
 (with-sformat-lex
   (format "x is: ${x} and y is: ${y}" 'lisp-val)))

or I could use lex-val.

I guess I could start adding more dynamic options to format to control
how things are output?

[magnars]

What I want are fewer dynamic options and instead a cleaner API. Functions
that do one thing.

On Mon, Apr 29, 2013 at 3:32 PM, Nic Ferrier notifications@github.comwrote:

The only trouble with that is that I think there are two things that
would be useful, lexical access and lexical access with Lisp output:

I'm using this code right now:

(defvar lexical-value-when-dynamic :error
"How `lexical-value' should act in dynamic scope.

Valid values are `:error', which is the default and causes
`lexical-value' to error when called in dynamic scope, or
`:symbol-value' which causes the `symbol-value' function to be
called for the symbol or `nil' which causes nil to be returned.")

(defmacro lexical-value (lexical-symbol)
"What is the value of the LEXICAL-SYMBOL specified?"
(let ((pv (make-symbol "pv"))
(sv (make-symbol "snv")))
`(let ((,pv (lambda ())))
(if (eq 'closure (car ,pv))
(let ((value
(assoc ,lexical-symbol (cadr ,pv))))
(when value (cdr value)))
(case lexical-value-when-dynamic
(:error (error "not in a lexical environment"))
(:symbol-value (symbol-value ,lexical-symbol))
(t nil))))))

(defmacro with-sformat-lex (&rest body)
(declare (debug (&rest form))
(indent 0))
`(flet ((lex-val (var)
(let ((lexical-value-when-dynamic :symbol-value)
(variable (intern var)))
(lexical-value variable)))
(lisp-val (var) (format "%S" (lex-val var))))
,@body))

So I can go:

(let ((x 1)
(y '(a b c)))
(with-sformat-lex
(format "x is: ${x} and y is: ${y}" 'lisp-val)))

or I could use lex-val.

I guess I could start adding more dynamic options to format to control
how things are output?

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/27#issuecomment-17166575
.

[nicferrier]

Do you? I like all that being able to change the behaviour of things by let binding and such. It's fun.

[nicferrier]

How about this:

(defmacro s-lex-format (format-str)
  (let ((pv (make-symbol "pv")))
    `(s-format
      ,format-str
      (let ((,pv (lambda ())))
        (if (eq 'closure (car ,pv))
            (lambda (var-name)
              (let ((value 
                     (assoc (intern var-name) (cadr ,pv))))
                (when value (cdr value))))
            (lambda (var-name)
              (case lexical-value-when-dynamic
                (:error (error "not in a lexical environment"))
                (:symbol-value (symbol-value
                                (intern var-name)))
                (t nil))))))))

(let ((lexical-value-when-dynamic :symbol-value)
      (x "1"))
  (s-lex-format "${x}"))

My only concern with this is that often you want the lex value to be lisp printed ("%S" instead of "%s") and that's not possible here. It could be done with a switch or a dyn var.

[magnars]

It's too convoluted for me. I would be a happy man if I could just have a formatting function that grabs content off the current scope. But come to think of it, maybe that's just concat, with " " separating the keys instead of ${}. How is ${} any better?

[nicferrier]

For all the reasons that s-format is better. My use case is this:

;;; ${name}.el --- ${desc}

${copy}

${decl}

;;; Commentary:

${commentary}

;;; Code:

${defn-code}

${prvide-code}
;;; ${name}.el ends here

Code that with concat and see how happy you are :-)

[magnars]

Haha, you're right. That would be terrible. :-)

On Mon, Apr 29, 2013 at 11:18 PM, Nic Ferrier notifications@github.comwrote:

For all the reasons that s-format is better. My use case is this:

;;; ${name}.el --- ${desc}

${copy}

${decl}

;;; Commentary:

${commentary}

;;; Code:

${defn-code}

${prvide-code}
;;; ${name}.el ends here

Code that with concat and see how happy you are :-)

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/27#issuecomment-17195146
.

[nicferrier]

It seems like a standard templating problem to me. And I've never really got how we can fix that with simple Lisp. Maybe there is a better solution but I'm not aware of it.