7. Recursive procedures are not handled. This restriction encompasses all cases of a function designator appearing in the actual parameter part of a call of the same function, unless that function is a standard function. Thus f(f(x)) is not permitted in general, but sin(sin(x)) is allowed.
There are two distinct modes of operation: ALGO and ALDAP.
ALGO is a compile-and-execute mode in which the two phases cannot be separated. The Algol program is translated into a machine language program in core memory, and execution of the program immediately and automatically follows. There is no assembly program phase.
ALDAP makes use of the CODAP assembly program facilities. It is possible to compile procedures separately and reference them from an Algol program. The procedures may be written in Algol, CODAP or Fortran. This provision is made possible with the aid of the external declaration discussed in section V.
The ALGO mode provides significantly faster compilation than the ALDAP mode for most programs. The target programs produced in the two modes are essentially the same. In the ALGO mode, program checkout may be done at the Algol language level. In the ALDAP mode, checkout may also be done at the machine and assembly language levels, and modifications may be made at these levels.
There are seven standard procedures for input-output, five for intermediate tape, and three for checking tape conditions. Two declarations, format and list, are additions to the language.
The input-output procedures are: READ, PAGE, PRINT, WRITE, PUNCH, INPUT, and OUTPUT.
The READ procedure is used to input numbers and Boolean values. A READ statement has the form
where n is any positive integer and each Vk is a variable. For example, the statement
will input values into the four variables listed. For inputing values into an array, a statement such as the following might be used:
for I := 1 step 1 until 100 do READ (A[I]) .
The READ procedure inputs numbers and truth values. A number must be a legal Algol number (although an E may be substituted for the symbol ₁₀). For input into a Boolean variable, the truth values true and false are accepted; also, a non-negative number or a plus sign is interpreted as false and a negative number or a minus sign is interpreted as true. A blank is read as zero.
