It may be inconvenient in some cases to write down all of the expressions explicitly. The loop expression[1] may be used as a shorthand device in a list. It is an Algol-like construction of which the following is an example:
for I := 1 step 1 until 1000 do A[I] .
This is equivalent to the list
A[1], A[2], ..., A[1000] .
The entity following do in a loop expression may itself be a list, but this list must be enclosed in parentheses if it contains more than one member.
The loop expression
for I := 1 step 1 until 1000 do (A[I], B[I])
is equivalent to the list
A[1], B[1], A[2], B[2], ..., A[1000], B[1000] .
The loop expression