spurious "unbound variable" error when variable is bound to NOBIND (e.g., in MAPATOMS with interpreted fn) about medley

[masinter]

\INTERPRETER1 in LLINTERP changes the stack frame of its caller to look like it's bound the "special" variable FOO, But the value is the symbol NOBIND which is 1 (?!). "There's a comment Note: area is initialize to NIL's (zero), so end of nametable already has its zeroes.d"

[nbriggs]

It's correct that NIL and NOBIND are the first two atoms at indexes 0 and 1 (while T is 0114Q), that's hardwired into the code.

[masinter]

I don't remember the convention that unbound atoms are bound to NOBIND? But this is' Broken As Designed because NOBIND is an atom and so FOO is bound to NOBIND. (LET ((FOO 'NOBIND)) (LIST FOO)) gives the same error (Interlisp interpreter only -- the Common Lisp interpreter uses lexical binding and compiled code doesn't need to look up for the bindings on the stack

[nbriggs]

Ah, obvious when you point it out. If you compile the (INTERLISP) function incorporating the above code it works fine, it's just the interpreted version that fails. Thanks.

[masinter]

this is a fundamental of the Interlisp interpreter

[masinter]

Implementation doesn't match documentation.

[masinter]

while it's a mystery why this choice was made....