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Re: Newbie Packaging Question

From: Tobias Geerinckx-Rice
Subject: Re: Newbie Packaging Question
Date: Sat, 11 May 2019 02:40:33 +0200


Brian Woodcox wrote:
I have a question regarding packaging.

Say I have the following in my sample.scm file:

(define commit "a1ee2ebf087768b5fbffa07f50a294ad9c8ee600")

(define version-date “201903271913”)

and then

(define-public test-me
  (name “test-me”)
  (version commit)
  (source …
               . etc...

In my modify-phases %standard-phases, I am trying to use substitute* to patch some files with the version-date define outside my package.

Is this not possible, I always get an unbound variable error.

You've omitted one of the interesting parts (the one where the error happens), but I suspect it's something roughly like this:

    (modify-phases %standard-phases
     (add-after 'unpack 'uh-oh
      (lambda _
       (substitute* ""
        (("198309270000") version-date))
       #t))))) ;          ^^^^^^^^^^^^

(If not: forgive & ignore the basic Scheme lecture below and please paste your full package expression :-)

What's happening here is that the value of ARGUMENTS is being *quoted* (by the ‘'’ just after ARGUMENTS), meaning that is is not immediately evaluated, but passed to the ‘build stage’ as-is. And since VERSION-DATE isn't bound (defined) in the build stage's environment, the builder will return the error you're seeing.

Luckily, this is easily fixed:

    (modify-phases %standard-phases
     (add-after 'unpack 'uh-oh
      (lambda _
       (substitute* ""
        (("198309270000") ,version-date))
       #t))))) ;          ^

Two subtle changes here:

- The ‘'’ (quote) has been changed into a ‘`’ *quasiquote*, which is identical to quote except that it allows *unquoting* inside the quoted expression.

- This unquoting is done by adding ‘,’ to VERSION-DATE. Any book on Scheme will explain it much better than I can, but here it basically says that you want to send the currently bound *value* of VERSION-DATE to the builder, not the variable name.

(If you've written your package by copying an existing one, you might already be using quasiquote without realising it, and all that's missing is an unquote.)

Kind regards,


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