R help - Feb 2005 - Strange parsing behavior of an else condition

Dear R users,

can anybody explain the reason, why the first piece of code
below gives a parsing error, while the other two variations
work?

# Gives a parsing error
x <- 1
if (x < 0)
  {
    y <- 1
  }
else # Error occurs at this line
  {
    y <- -1
  }


# This works
x <- 1
{
  if (x < 0)
    {
      y <- 1
    }
  else
    {
      y <- -1
    }
}

# This works too
x <- 1
if (x < 0)
  {
    y <- 1
  } else
  {
    y <- -1
  }

Christian

On Tue, 8 Feb 2005, Christian Lederer wrote:
> can anybody explain the reason, why the first piece of code
> below gives a parsing error, while the other two variations
> work?
>
> # Gives a parsing error
> x <- 1
> if (x < 0)
>   {
>     y <- 1
>   }
> else # Error occurs at this line
>   {
>     y <- -1
>   }
>
>
> # This works
> x <- 1
> {
>   if (x < 0)
>     {
>       y <- 1
>     }
>   else
>     {
>       y <- -1
>     }
> }
>
> # This works too
> x <- 1
> if (x < 0)
>   {
>     y <- 1
>   } else
>   {
>     y <- -1
>   }
>
help("if")

In the first case, the if expression is complete prior to
the else, hence the error. The second case completes since
the outer enclosing brace has not been processed. The third
case completes since the else is on the same line as brace
closing if expression and else expression not yet processed.

There may also be issues whether you're running interactively
or not. Recommend not using Whitesmith style brace formatting
with R or S-plus. IMO, the following formatting style works
best:

sety <- function(x) {
    if (x < 0) {
        y <- 1
    } else {
        y <- -1
    }
}

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