Is “for” the best term for a loop?

The use of the term for to designate counting loops likely evolved from the use of für in Superplan. It has caught on in most programming languages, but is it the most appropriate term for a loop? The problem with the widely adapted for is that it is just not expressive. Consider the use of for in the following C statement:

for (x=1; x<=1000; x=x+1){
   ...
}

What it does is imply that x has the values 1→1000, but it doesn’t really suggest something will be done. That this is implied by including a statement after the fact is fine, but it isn’t as obvious. The use of for in a loop really implies that it is “used as a function word to indicate an actual or implied enumeration or selection“. It should really be used with the term do, to imply something is being implemented. Likely the design of C assumed this, and just truncated the word do, yet this lessens the readability of the loop.

The first decisive use of for as a loop qualifier likely came in ALGOL-60.

for x := 1 step 1 until 1000 do
begin
   ...
end

However the loop still uses the verb do to imply something will be done. Using for by itself does not really imply a loop is to occur, at least from the perspective of descriptive terms. It is this reason that novice programmers learning C have difficulty with loops (well that and the obscure nature of the for loop statement in C). Consider instead the Fortran version of the loop:

do x = 1,1000
   ...
end do

The term do does imply that something will be done. The “x=1,1000” just assigns constraints on the loop variable.

Maybe a better term would be one that suggests repetition is to be performed: loop (Ada) , or repeat (Pascal) perhaps? In Ada the for loop setup certainly begins with for, but ends with the keyword loop, and the loop itself is terminated with the phrase end loop. This is the same for the while loop, and the generic loop. Here is the sample for loop in Ada:

for x in 1 .. 1000 loop
   ...
end loop

An even better idea would be to create a structure which indicates it is a loop directly, with differing constraints. For example the term loop used by Ada is a good starting point. From a computing point-of-view a loop implies repetition.

loop with x=1..1000
   ...
end loop

The use of the preposition with helps to express the spatial relationship of the variable controlling the loop. It is also easy to extend this one piece of syntax to a family of loops. For example:

loop while x<1000
   ...
end loop

loop until x < 0
   ...
end loop

The choices made for control structures can have a great impact on the learnability of a language. The use of the term do as in Fortran, implies something is to be done.