78. stringproc

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78.1 Introduction to string processing

stringproc.lisp enlarges Maximas capabilities of working with strings and adds some useful functions for file in/output.

For questions and bugs please mail to van.nek at arcor.de .

In Maxima a string is easily constructed by typing "text". stringp tests for strings.

(%i1) m: "text";
(%o1)                         text
(%i2) stringp(m);
(%o2)                         true

Characters are represented as strings of length 1. These are not Lisp characters. Tests can be done with charp (respectively lcharp and conversion from Lisp to Maxima characters with cunlisp).

(%i1) c: "e";
(%o1)                           e
(%i2) [charp(c),lcharp(c)];
(%o2)                     [true, false]
(%i3) supcase(c);
(%o3)                           E
(%i4) charp(%);
(%o4)                         true

All functions in stringproc.lisp that return characters, return Maxima-characters. Due to the fact, that the introduced characters are strings of length 1, you can use a lot of string functions also for characters. As seen, supcase is one example.

It is important to know, that the first character in a Maxima-string is at position 1. This is designed due to the fact that the first element in a Maxima-list is at position 1 too. See definitions of charat and charlist for examples.

In applications string-functions are often used when working with files. You will find some useful stream- and print-functions in stringproc.lisp. The following example shows some of the here introduced functions at work.

Example:

openw returns an output stream to a file, printf then allows formatted writing to this file. See printf for details.

(%i1) s: openw("E:/file.txt");
(%o1)                    #<output stream E:/file.txt>
(%i2) for n:0 thru 10 do printf( s, "~d ", fib(n) );
(%o2)                                done
(%i3) printf( s, "~%~d ~f ~a ~a ~f ~e ~a~%", 
              42,1.234,sqrt(2),%pi,1.0e-2,1.0e-2,1.0b-2 );
(%o3)                                false
(%i4) close(s);
(%o4)                                true

After closing the stream you can open it again, this time with input direction. readline returns the entire line as one string. The stringproc package now offers a lot of functions for manipulating strings. Tokenizing can be done by split or tokens.

(%i5) s: openr("E:/file.txt");
(%o5)                     #<input stream E:/file.txt>
(%i6) readline(s);
(%o6)                     0 1 1 2 3 5 8 13 21 34 55 
(%i7) line: readline(s);
(%o7)               42 1.234 sqrt(2) %pi 0.01 1.0E-2 1.0b-2
(%i8) list: tokens(line);
(%o8)           [42, 1.234, sqrt(2), %pi, 0.01, 1.0E-2, 1.0b-2]
(%i9) map( parse_string, list );
(%o9)            [42, 1.234, sqrt(2), %pi, 0.01, 0.01, 1.0b-2]
(%i10) float(%);
(%o10) [42.0, 1.234, 1.414213562373095, 3.141592653589793, 0.01,
                                                     0.01, 0.01]
(%i11) readline(s);
(%o11)                               false
(%i12) close(s)$

readline returns false when the end of file occurs.

Categories: Strings · Share packages · Package stringproc

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78.2 Functions and Variables for input and output

Example:

(%i1) s: openw("E:/file.txt");
(%o1)                     #<output stream E:/file.txt>
(%i2) control: 
"~2tAn atom: ~20t~a~%~2tand a list: ~20t~{~r ~}~%~2t\
and an integer: ~20t~d~%"$
(%i3) printf( s,control, 'true,[1,2,3],42 )$
(%o3)                                false
(%i4) close(s);
(%o4)                                true
(%i5) s: openr("E:/file.txt");
(%o5)                     #<input stream E:/file.txt>
(%i6) while stringp( tmp:readline(s) ) do print(tmp)$
  An atom:          true 
  and a list:       one two three  
  and an integer:   42 
(%i7) close(s)$

Function: close (stream): Closes stream and returns true if stream had been open.

Categories: File input · File output · Package stringproc

Function: flength (stream): Returns the number of elements in stream.

Categories: File input · File output · Package stringproc

Function: fposition (stream)
Function: fposition (stream, pos): Returns the current position in stream, if pos is not used. If pos is used, fposition sets the position in stream. pos has to be a positive number, the first element in stream is in position 1.

Categories: File input · File output · Package stringproc

Function: freshline ()
Function: freshline (stream): Writes a new line (to stream), if the position is not at the beginning of a line. See also newline.

Categories: File output · Package stringproc

Function: newline ()
Function: newline (stream): Writes a new line (to stream). See sprint for an example of using newline(). Note that there are some cases, where newline() does not work as expected.

Categories: File output · Package stringproc

Function: opena (file): Returns an output stream to file. If an existing file is opened, opena appends elements at the end of file.

Categories: File output · Package stringproc

Function: openr (file): Returns an input stream to file. If file does not exist, it will be created.

Categories: File input · Package stringproc

Function: openw (file): Returns an output stream to file. If file does not exist, it will be created. If an existing file is opened, openw destructively modifies file.

Categories: File output · Package stringproc

Function: printf (dest, string)

Function: printf (dest, string, expr_1, ..., expr_n)

Makes the Common Lisp function FORMAT available in Maxima. (From gcl.info: "format produces formatted output by outputting the characters of control-string string and observing that a tilde introduces a directive. The character after the tilde, possibly preceded by prefix parameters and modifiers, specifies what kind of formatting is desired. Most directives use one or more elements of args to create their output.")

The following description and the examples may give an idea of using printf. See a Lisp reference for more information.

   ~%       new line
   ~&       fresh line
   ~t       tab
   ~$       monetary
   ~d       decimal integer
   ~b       binary integer
   ~o       octal integer
   ~x       hexadecimal integer
   ~br      base-b integer
   ~r       spell an integer
   ~p       plural
   ~f       floating point
   ~e       scientific notation
   ~g       ~f or ~e, depending upon magnitude
   ~h       bigfloat
   ~a       uses Maxima function string
   ~s       like ~a, but output enclosed in "double quotes"
   ~~       ~
   ~<       justification, ~> terminates
   ~(       case conversion, ~) terminates 
   ~[       selection, ~] terminates 
   ~{       iteration, ~} terminates

Note that the selection directive ~[ is zero-indexed. Also note that the directive ~* is not supported.

(%i1) printf( false, "~a ~a ~4f ~a ~@r", 
              "String",sym,bound,sqrt(12),144), bound = 1.234;
(%o1)                 String sym 1.23 2*sqrt(3) CXLIV
(%i2) printf( false,"~{~a ~}",["one",2,"THREE"] );
(%o2)                          one 2 THREE 
(%i3) printf(true,"~{~{~9,1f ~}~%~}",mat ),
          mat = args(matrix([1.1,2,3.33],[4,5,6],[7,8.88,9]))$
      1.1       2.0       3.3 
      4.0       5.0       6.0 
      7.0       8.9       9.0 
(%i4) control: "~:(~r~) bird~p ~[is~;are~] singing."$
(%i5) printf( false,control, n,n,if n=1 then 0 else 1 ), n=2;
(%o5)                    Two birds are singing.

If dest is a stream or true, then printf returns false. Otherwise, printf returns a string containing the output.

Categories: File output · Package stringproc

Function: readline (stream): Returns a string containing the characters from the current position in stream up to the end of the line or false if the end of the file is encountered.

Categories: File input · Package stringproc

Function: sprint (expr_1, …, expr_n)

Evaluates and displays its arguments one after the other `on a line' starting at the leftmost position. The numbers are printed with the '-' right next to the number, and it disregards line length. newline(), which will be autoloaded from stringproc.lisp might be useful, if you whish to place intermediate line breaking.

Example:

(%i1) for n:0 thru 19 do sprint( fib(n) )$
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181
(%i2) for n:0 thru 22 do ( 
         sprint(fib(n)), if mod(n,10)=9 then newline() )$
0 1 1 2 3 5 8 13 21 34 
55 89 144 233 377 610 987 1597 2584 4181 
6765 10946 17711

78.1 Introduction to string processing
78.2 Functions and Variables for input and output
78.3 Functions and Variables for characters
78.4 Functions and Variables for strings

78. stringproc

78.1 Introduction to string processing

78.2 Functions and Variables for input and output

78.3 Functions and Variables for characters

78.4 Functions and Variables for strings