ℙ𝕖𝕡 🙴 ℕ𝕠𝕞

By weaving, we maintain the order of the universe. Kogi People

the ℙ𝕖𝕡 "lines" register

About the automatic line counter register in the pep machine.

The pep virtual machine maintains an automatic count of the number of lines which have been read from the input stream. This line-count is kept in the lines register of the virtual machine. You can access this register with the lines command and the nolines command.

The lines command adds the current count in the lines register to the end of the workspace buffer (as text). The nolines command resets the lines counter to zero (the lines counter is automatically initialised at zero at the start of the nom script).

   read; until "\n"; put;
   # a trick to see if the line contains the text "mark"
   replace "mark" "";
   !(==) { a+; nolines; }
   clear;
   (eof) { 
     count;
     # the accumulator indicates if the text 'mark' occurred or not
     !"0" {
       clear; add "lines after 'mark':"; lines; add "\n"; 
       print; quit;
     }
     clear; add "No 'mark'."; print; quit;
   }
 

notes

The reason that the number of lines read from the input-stream has an automatically updated register in the machine is because ℙ𝕖𝕡 🙵 ℕ𝕠𝕞 is designed for recognising, parsing, translating, transpiling, compiling and error checking text patterns and context-free and context-sensitive formal languages. In the context of error-checking the syntax or the validity of the text input, it is very useful to keep track of the current line number so that helpful “error” messages can be printed to show the language writer where he or she went wrong.

The function of the lines register could be fulfilled by the accumulator register as follows

   read; "\n" { a+; } clear;
   (eof) {
     add "Found "; count; add " lines. See ya \n"; 
     print; quit;
   }
 

But that would clog up the accumulator register and we could not use it for anything else.

The pep interpreter actually still accepts “ll” as an alias for the lines command, but I will begin to remove that command alias

(it has already been removed from some translation scripts).

see also

The nom commands lines nolines chars nochars et.