Re: First language with conditional assignment?

> Does anyone know what the earliest languages supporting conditional
> assignment were?


Unlike the other followups, I understand the question not as one about
dynamic LHS determination but really as "conditional assignment".


The following conditional assignment idioms come to my mind:


(1) ICON [Griswold & Griswold, (1980ies)] knows a possible "&null" value
for (typically) uninitialized variables. The expression


(/x) := 22


will assign to x only if x is still &null so far. Contrarily,


(\x) := 22


will only overwrite x if set already. (Both expression "fail" otherwise
which is nothing catastrophic in ICON.)


(2) Bourne/POSIX sh (1970ies), pretty much the same:


${foo:=22} # assign default value if still null


(3) Assemblers: "test-and-set" instructions, most often used to implement
atomic locks. I draw a blank when I try to date this using wikipedia or
google. I remember to have had it available in a simulated /370.


Undoubtly, many variations of this must exist.


Martin Neitzel
[Test and set was in the S/360 architecture in the early 1960s. Dunno
if it was on earlier machines or if they just did it implicitly using
add to memory. -John]

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