The next time someone posts a History of History of Lisp threads[0], we can officially begin tracking the History of History of History of Lisp threads :)
The bibliography mentions Herbert Stoyan "wrote several chapters" about the history of LISP, but doesn't give more details.
Professor Stoyan, who held the chair of Artificial Intelligence at Friedrich Alexander University of Erlangen-Nuremberg, actually donated his LISP history
paper to the Computer History Museum.
> A paper defining conditional expressions and proposing their use in Algol was sent to the Communications of the ACM but was arbitrarily demoted to a letter to the editor, because it was very short.
Someone should have realized a short letter from John McCarthy is likely more significant than most long papers from other researchers.
The if-expression and if-statement are different things.
if-statements result in conditional execution of different statements, but do not return values themselves. Borrowing C's syntax for if statements the following is not allowed:
int next = if (odd(current)) { 3*current + 1; } else {current / 2;};
That's not a valid expression in C.
if-expressions return a value, and C does have an if-expression with its ternary operator:
int next = odd(current)? 3*current + 1 : current / 2;
if-statements are ubiquitous to nearly every programming language. Even when they aren't done with the if keyword and more familiar syntax, even unstructured languages with conditional branching instructions and goto permit you to write something like an if-statement (just disguised by the usually more verbose unstructured form).
if-expressions are less universally available (though I'm unsure of any higher-level-than-assembly language still in popular use that doesn't have an if-expression equivalent).
How does this differ semantically from the C ternary operator? Not syntactically, in its outcome and expression of a testable boolean clause, and a left or right side choice which is the assignment value?
Algol 60 had lexical scoping in 1960 (while Lisp was in development) and this was known to be equivalent to the lambda calculus by the folks working on it by 1965 or so -
https://dl.acm.org/doi/10.1145/363744.363749
I think the consensus is that Scheme was the first Lisp to fully embrace lexical scope, in 1975?
There is also the fact that if you have assoc lists, you can trivially easily write a badly performing but correctly lexical lisp interpreter in dynamic lisp, and I suspect this was consciously known. Maybe not enough people cared?
I believe Algol 60 had downward-funarg-only lexical scoping, whereby if you return a function with a captured environment, the coach turns into a pumpkin (unless it is somehow disallowed).
Lambda Calculus specifies the real deal; functions can calculate functions.
McCarthy praised Herbert Stoyan's historical work on early Lisp http://www.mcjones.org/dustydecks/archives/2010/07/29/185/ https://web.archive.org/web/20050617031004/http://www8.infor... above his own "History of Lisp": "Stoyan's reading of the early LISP documents gives a more accurate picture than my own memories turned out to have given." http://www-formal.stanford.edu/jmc/history/
For HOPL 2 in 1993 Guy Steele and Richard P. Gabriel wrote "The Evolution of Lisp" https://www.dreamsongs.com/Files/HOPL2-Uncut.pdf which continued the story up to about 1992-3.