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https://github.com/AdamNiederer/metamorph

Transform your code in turing-complete ways
https://github.com/AdamNiederer/metamorph

emacs emacs-lisp metaprogramming transforming-files

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Transform your code in turing-complete ways

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README 

        
* metamorph

Higher-order buffer transformations for Emacs.



** Usage

Say you're writing some lovely code for your new libc implementation:



#+BEGIN_SRC c

  void free(void* ptr) {

    void* prev_freelist_ptr = (void*)*(size_t**)(ptr - 24);

    void* next_freelist_ptr = (void*)*(size_t**)(ptr - 16);

    size_t this_size = *(size_t*)(ptr - 8);



    // Set prev->next to this->next and next->prev to this->prev

    *(size_t*)(prev_freelist_ptr - 24) = next_freelist_ptr;

    *(size_t*)(next_freelist_ptr - 16) = prev_freelist_ptr;

  }

#+END_SRC



But all of a sudden, you want to add a new feature, and change the pointer

offsets above:



#+BEGIN_SRC c

    void free(void* ptr) {

      void* prev_freelist_ptr = (void*)*(size_t**)(ptr - 32);

      void* next_freelist_ptr = (void*)*(size_t**)(ptr - 24);

      size_t this_size = *(size_t*)(ptr - 16);

      size_t magic_number = *(size_t*)(ptr - 8);



      // Check for freelist corruption

      assert(magic_number == 0xdeadbeefcafefade);



      // Set prev->next to this->next and next->prev to this->prev

      *(size_t*)(prev_freelist_ptr - 32) = next_freelist_ptr;

      *(size_t*)(next_freelist_ptr - 24) = prev_freelist_ptr;

    }

#+END_SRC



You could use ~replace-string~ three times for each number literal in your code

Or, you could use ~(metamorph-map-region "[0-9]+" "(- %i 8)")~.



Metamorph provides a powerful way to transform your buffer contents - perform

base conversions, increment numbers, transform every nth match, and more. Use

any Emacs Lisp function to transform your data - the sky is the limit.



Metamorph's principal function, ~metamorph-map-region~ will prompt you for a

regular expression, and a lisp expression. It will then replace everything

matching the regular expression in your region with the result of the lisp

expression. You can use the following variables in the lisp expression:



- ~%~ is the matched string without any additional processing

- ~%i~ is the matched string's value as an integer

- ~%0~ is an index which starts at zero, and increments for each match

- ~%n~ is the total number of matches



Additionally, if a prefix argument is specified, the following

values may be used in TRANSFORM:



- ~%!~ is the matched string's value as a lisp expression

** Security

When a prefix argument is provided to ~metamorph-map-region~, metamorph reads

all strings matching the regular expression, and will gladly evaluate them as

Lisp if ~%!~ is included in the transformation expression. Because of the

security implications of such behavior, it is recommended to not provide a

prefix argument or use ~%!~ on untrusted buffers.



Calling ~(read %)~ in your transformation expression will also nullify the

safeguards in ~metammorph-map-region~ and carries the same security implications

as providing a prefix argument and using ~%!~.

** Cleanup

Metamorph removes all preview overlays when either both the regular expression

and transformation are entered, or ~C-g~ is pressed. If you manage to leave the

minibuffer without doing either of those things, you can call

~metamorph-cleanup~ to remove the preview overlays.