ChStr is a built-in type of character strings.  It implements string
constants, single character input, string output, concatenation,
and substring operations.  Functions to convert between strings of length 1,
and the ASCII code of the chracter they contain are also present.
See the "strings" entry for more information about string constants and
concatenation.

    ChStr: type CS {
	characters;
	'' :     func [] val CS;
	. :      func [val CS; val Short] val Short;
        := :     func [var CS; val CS] val CS;
        <> :     func [val CS; val CS] val Boolean;
        = :      func [val CS; val CS] val Boolean;
        < :      func [val CS; val CS] val Boolean;
        > :      func [val CS; val CS] val Boolean;
        <= :     func [val CS; val CS] val Boolean;
        >= :     func [val CS; val CS] val Boolean;
        In:      func [val Short] val CS;
        New:     func [] var CS;
	New:     func [val CS] var CS;   (* initializes to arg value *)
        Out:     func [val CS] val Short;
        V        func [var CS] val CS;
        ^* :     func [x,y: val CS] val CS;
        getchar: func [var Void] val CS;
        len:     func [val CS] val Short;
        put:     func [val CS] val CS;
        substr:  func [val CS; start,length: val Short] val CS;
    };

The "substr" operation requires a string, a starting position
(0 for the beginning) and a length.  It returns the substring starting
at the indicated position and of the indicated length (shorter if the
original string is shorter than start+length).  The "Out" function
returns the ASCII code of the first character in the string.
The expression "s.i" evaluates to the ASCII code of ith character of s.
"Out[s]" is equivalent to "s.0".  The "In" function returns a one character
string.  The ASCII code of that character is the argument modulo 256.

Note that NULL is used as a termination character.  Thus an explicit
NULL in the middle of a string will cause the rest of the string
to be ignored.

Implementation note:  The implementation is compatible with C (for values).
As a result, 'len' and 'substr' having running times proportional to the
length of the string.  The same applies to the index operation ".", except
in the presence of -O in the non-Vax implementation.