This line in MUMPS is not only valid, it also actually does something potentially useful: s:foo'="" foo(foo)=foo It's actually a bit tricky to explain wha

This line in MUMPS is not only valid, it also actually does something potentially useful: s:foo'="" foo(foo)=foo It's actually a bit tricky to explain what it does. Everything in MUMPS is effectively a tree. Each tree has a value in the "root node" and you can set it like this: set foo="hello" You can also put data deeper into the tree: set foo("fizz")="buzz" So if something is passed to you and you want to know if you can treat it as a string, you test to see if it's a null string: if foo'="" do [something] ('= means !=) Two more features: 1) Almost every directive can be reduced to one letter. 2) If I want to quit based on a condition, I can do either if condition quit or quit:condition So the line above is more legibly written as if foo'="" set foo(foo)=foo So if foo="bar", it's equivalent to: set foo("bar")="bar"