System keys

Apart from the single letter 'C' which marks a comment card and could be considered to be a system key, there are eight system keys. They are listed below with their arguments (if any) and their actions.

LIST

(no argument) Turn on listing of data cards as recognized by FFREAD; also output error messages.

NOLIst

(no argument) Turn off listing; don't print error messages.

READ

(one integer argument) Read input from FORTRAN logical unit as given by the integer. The current input unit is pushed on a stack. Reading stops at end-of-file or when the data cards STOP or END are encountered.

WRITe

(one integer argument) Write listing and error messages to FORTRAN logical unit as given by the integer (if listing is enabled).

STOP

(no argument) Unconditionally stop reading data cards and return to the user.

END

(no argument) If reading a file via READ, return to the previous unit (pop the stack). Otherwise, it has the same effect as STOP.

HOLL

(one character from the set ('=$()"/) Change the character delimiting a hollerith value.

KEYS

(no argument) List all system and user keys when the STOP condition is reached. This is done independent of the LIST flag setting.

For these keys, any abbreviation between their shortest form (indicated by upper case in the list above) and the number of significant characters as defined above is recognized.