[lispm]

The designers argued that a million-line software (the OS + basic applications) was easier to debug/develop without having TCO everywhere. It makes stack traces useless, unless one thinks of clever ways to keep tail calls recorded, which makes it complex/tricky. The basic machine architecture is a stack machine with compact and nice instructions. Stack traces were useful then. The compiler also was not very sophisticated when it comes to optimizations.

[ScottBurson]

I've long thought the right thing for Common Lisp would be to provide a way to declare sets of functions such that any tail call from one member of the set to another would be TCO'd; all other calls would push stack. This lets you write sets of mutually tail-recursive routines without forcing TCO on the entire system.

[qwertyuiop924]

It's an entirely reasonable tradeoff, which I understand. But not having TCO is a strong negative from the language perspective, IMHO. Not an impossibly bad one, but it's really nice.