Herd
Herd is a simple interpreted programming language where everything is a value.
Disclaimer: This is a hobby language, and you probably shouldn't use it for anything important.
What makes Herd special?
In Herd, everything is pass-by-value, including lists and dicts. This means that when you pass a list or dict to a function, you can guarantee that the function won't modify your copy.
You can modify variables locally just like you would in an imperative language, but there will never be any side-effects on other copies of the value.
var foo = { a : 1 }; var bar = foo; // make a copy of foo set bar.a = 2 ; // modify bar (makes a copy) println foo.a bar.a; // prints 1 2
How does it work?
All reference types in Herd (e.g. strings, lists, dicts) use reference counting. Whenever you make a copy of a reference type, the reference count is incremented. Whenever you modify a reference type, one of two things happen:
If there's only one reference to the value, it can be modified in-place without making any copies. This is because the code doing the modification must be the only reference, so no other code will be able to observe the modification.
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