I'm six years late to the conversation, but I'm adding my own contribution because this is the page that I found in the search engine when looking for "setting [expr] dynamically". Perhaps others will find it here.

calc.zip

I made a new external object for my friend named [lotus ]. It's just a simple message database. Message-strings are stored in a file, one message per line, in the format "key message-string", where message-string is composed of one or more atoms (symbols or floats) separated by whitespace, and the key is either a symbol or a number. The database file can be edited outside Pd or it can be updated from within Pd. To retrieve a message-string from the database, only its key is needed.

[qlist ] and [textfile ], which are built in to Pd Vanilla, already provide an interface with files, so the value of [lotus ] is in its simplicity and single focus: it only does one thing, an associative memory array with permanent storage.

To complete the story, I've posted a demo patch which showcases [seq ], [purdie ] and [memorex ] working together and a video of the patch in operation. My friend says it's helpful in discovering and capturing novel note sequences.

My friend really likes [purdie ] (see above) for producing random note sequences. He says that sometimes the random sequence sounds good and he wishes he could hear it again. So I created a new object for him: [memorex ]. This object:has two modes of operation controlled by a replay toggle input. When replay is off, the input is passed through to the output while recording it in a memory buffer. When replay is on, the recorded input history is replayed in a loop.

My friend asked for an enhancement to [shuffle ]. He wanted to be able to add numbers to the random series. I decided to create a new object named [purdie ] which behaves as follows:

1. outputs a random series of integers, one for each bang
2. the series is initially empty -- there is no initial series of consecutive integers as with the [shuffle ] object
3. one or more integers can be added to the series between bangs
4. integers already in the series can be removed
5. the integers in the series need not be in a consecutive sequence
6. the series can be reset to its initial empty state

For convenience, the [purdie ] object can be loaded with a series of consecutive integers provided by another new object named [seq ], optionally with only one bang.

I tried registering at git.purrdata.net because they have a copy of the Motex library there. Thought I'd post the errors I've found and maybe submit a fix. Then maybe look for other work that needs to be done. But my registration request was rejected without explanation.

I'm new to Pure Data. A friend asked for help with the [shuffle ] external object, which was crashing on him.

When I checked the shuffle.c source code, I found several issues. The Motex library it belongs to has not been maintained for a decade and there is no longer a project site for it, so I'm not able to make a pull request with fixes. Instead, I wrote my own drop-in replacement from scratch: pd-shuffle.

I'm not sure what else to do besides posting it here. Advice welcome.