[6517] in s-news-athena
Where to put the + operator when continuing a line
daemon@ATHENA.MIT.EDU (Steven P. Millard)
Mon Feb 27 00:18:15 1995
Date: 26 Feb 95 23:51:34 EST
From: "Steven P. Millard" <74273.3130@compuserve.com>
To: S-news <S-news@utstat.toronto.edu>
Hi there,
Just a word of warning: when writing functions, do not continue an
expression on the next line with the "+" or "-" operators (put the
+ or - at the end of the first line), otherwise you can get unexpected
results. Here is a simplified example of one that got
me a couple of weeks ago. Compare the results of fcn1() and
fcn2():
Source files look like this:
---------------------------
"fcn1" <- function(x, y, z)
{
value <- x + y
+ z
value
}
"fcn2" <- function(x, y, z)
{
value <- x + y +
z
value
}
Inside S-PLUS, the functions look like this:
-------------------------------------------
> fcn1
function(x, y, z)
{
value <- x + y
+ z
value
}
> fcn2
function(x, y, z)
{
value <- x + y + z
value
}
Results look like this:
----------------------
> fcn1(1,2,3)
[1] 3
> fcn2(1,2,3)
[1] 6
Here is Bill Dunlap's (of StatSci) explanation:
----------------------------------------------
Splus will parse
a
+b
as two expressions, "a" and "+b", but will parse
a+
b
as one expression, "a+b". This is its intended behavior so
one can continue lines without special continuation or
expression termination characters. Whenever it reaches a newline
(or a semicolon, there is an expression terminator if one wants
to use it) it checks to see if the text it has so far can be
construed to be a complete expression. If so it says this
is an expression and the next line starts a new expression.
If not, it assumes the next line continues the current expression.
It does not look at the next line to determine whether the current
line is a complete expression or not (in interactive use, the
next line doesn't exist when that decision must be made).
--------------------------------------------------------------------------
--Steve M.
(~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~)
( _____________ )
( | *** | Steven P. Millard )
( | * | )
( | * * * | P robability, )
( | * * * | S tatistics & )
( | * | I nformation )
( | * | )
( | *** | 7723 44th Avenue NE )
( |___________| Seattle, WA 98115 USA )
( )
( Voice/FAX: (206) 528 - 4877 )
( E-mail: 74273,3130@CompuServe.COM )
(___________________________________________________________)
