a link an ISBL introduction would be nice

I could only find this https://www.dcs.warwick.ac.uk/people/academic/Meurig.Beynon/...

Nice! It has a succinct overview of the Relational Model before discussing ISBL.

There was a earlier thread today which is an interview with Chris Date where he mentions that QBE and ISBL are more "Relational" than SQL - https://news.ycombinator.com/item?id=39189015

Skip to page 11 in the PDF for examples.

    MEMBERS(NAME, ADDRESS, BALANCE)
    ORDERS(ORDER_NO, NAME, ITEM, QUANTITY)
    SUPPLIERS(SNAME, SADDRESS, ITEM, PRICE)

    1. Print the names of members in the red:
    LIST MEMBERS : BALANCE < 0 % NAME

    i.e. select members with negative balance and
    project out their names

I was looking for more algebraic relational languages this weekend after seeing some Youtube video about Cypher; the video used nice glyphs for showing complex Cypher queries which was far far more readable and nice that Cypher (let alone SQL). Unfortunately I cannot find the origin of those glyphs, so I started looking for languages. So I can add this one to the list, thanks.

And nice to see TCL again; I used to write a lot in it.

NB: The repo had its last commit 10 years ago. The `Makefile` doesn't work at all on ArchLinux.

It only works on Macs with the right username https://github.com/jbroll/isbl/blob/89f6d204e87632c734537baf...

But I guess there are quite some Macusers named John

... Unless you invoke the build with make PT=<whatever you need>, which will override the assignment inside the makefile. (This feature seems to be extremely easy to forget for some reason.)

Passed my QA checks, ship it!