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<TITLE>LambdaMOO Programmer's Manual - Subsequence Replacement</TITLE>
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<H4><A NAME="SEC21" HREF="ProgrammersManual_toc.html#TOC21">Replacing a Subsequence of a List or String</A></H4>
<P>
The subrange assigment replaces a specified subsequence of a list or string
with a supplied subsequence. The allowed forms are:
</P>
<PRE>
<VAR>variable</VAR>[<VAR>start-index-expr</VAR>..<VAR>end-index-expr</VAR>] = <VAR>result-expr</VAR>
<VAR>object-expr</VAR>.<VAR>name</VAR>[<VAR>start-index-expr</VAR>..<VAR>end-index-expr</VAR>] = <VAR>result-expr</VAR>
<VAR>object-expr</VAR>.(<VAR>name-expr</VAR>)[<VAR>start-index-expr</VAR>..<VAR>end-index-expr</VAR>] = <VAR>result-expr</VAR>
$<VAR>name</VAR>[<VAR>start-index-expr</VAR>..<VAR>end-index-expr</VAR>] = <VAR>result-expr</VAR>
</PRE>
<P>
As with indexed assigments, the first form writes into a variable, and the last
three forms write into a property. The same errors (<CODE>E_TYPE</CODE>,
<CODE>E_INVIND</CODE>, <CODE>E_PROPNF</CODE> and <CODE>E_PERM</CODE> for lack of read/write
permission on the property) may be raised. If <VAR>variable</VAR> does not yet have
a value (i.e., it has never been assigned to), <CODE>E_VARNF</CODE> will be raised.
As before, the <CODE>$</CODE> expression can be used in either <VAR>start-index-expr</VAR>
or <VAR>end-index-expr</VAR>, meaning the length of the original value of the
expression just before the <CODE>[...]</CODE> part.
</P>
<P>
If <VAR>start-index-expr</VAR> or <VAR>end-index-expr</VAR> is not an integer, if the value
of <VAR>variable</VAR> or the property is not a list or string, or <VAR>result-expr</VAR>
is not the same type as <VAR>variable</VAR> or the property, <CODE>E_TYPE</CODE> is
raised. <CODE>E_RANGE</CODE> is raised if <VAR>end-index-expr</VAR> is less than zero
or if <VAR>start-index-expr</VAR> is greater than the length of the list or string
plus one. Note: the length of <VAR>result-expr</VAR> does not need to be the same
as the length of the specified range.
</P>
<P>
In precise terms, the subrange assigment
<PRE>
<VAR>v</VAR>[<VAR>start</VAR>..<VAR>end</VAR>] = <VAR>value</VAR>
</PRE>
<P>
is equivalent to
<PRE>
<VAR>v</VAR> = {@<VAR>v</VAR>[1..<VAR>start</VAR> - 1], @<VAR>value</VAR>, @<VAR>v</VAR>[<VAR>end</VAR> + 1..$]}
</PRE>
<P>
if <VAR>v</VAR> is a list and to
<PRE>
<VAR>v</VAR> = <VAR>v</VAR>[1..<VAR>start</VAR> - 1] + <VAR>value</VAR> + <VAR>v</VAR>[<VAR>end</VAR> + 1..$]
</PRE>
<P>
if <VAR>v</VAR> is a string.
</P>
<P>
The assigment expression itself returns the value of <VAR>result-expr</VAR>. For
the following examples, assume that <CODE>l</CODE> initially contains the list
<CODE>{1, 2, 3}</CODE> and that <CODE>s</CODE> initially contains the string "foobar":
</P>
<PRE>
l[5..6] = {7, 8} error--> E_RANGE
l[2..3] = 4 error--> E_TYPE
l[#2..3] = {7} error--> E_TYPE
s[2..3] = {6} error--> E_TYPE
l[2..3] = {6, 7, 8, 9} => {6, 7, 8, 9}
l => {1, 6, 7, 8, 9}
l[2..1] = {10, "foo"} => {10, "foo"}
l => {1, 10, "foo", 6, 7, 8, 9}
l[3][2..$] = "u" => "u"
l => {1, 10, "fu", 6, 7, 8, 9}
s[7..12] = "baz" => "baz"
s => "foobarbaz"
s[1..3] = "fu" => "fu"
s => "fubarbaz"
s[1..0] = "test" => "test"
s => "testfubarbaz"
</PRE>
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