Reads a line from the read stream and outputs that line as a word (without the end-of-line sequence). The output is a single word even if the line contains spaces, brackets, etc. A blank line is output as the empty word. If the read stream is a file and the last character in the file is not an end-of-line sequence, then READWORD treats the end-of-file as an end-of-line. After the file as been completely read, READWORD outputs the empty list (not the empty word).
READWORD processes backslash, vertical bar, and tilde characters in the read stream. In the case of a tilde used for line continuation, the output word does include the tilde and the newline characters. Vertical bars in the line are also preserved in the output. Backslash characters are not preserved in the output, except for the ones that follow a backslash. This strange behavior enables the resulting word to be parsed into a list with PARSE in a way that preserves the normal sematics.
The notion that vertical bars are both processed and preserved in the output warrants a fuller explanation. In processing, vertical bars retain their ability to allow a single line of text to include newline characters. So if a newline follows a vertical bar, READWORD continues reading more text until it finds a vertical bar that closes the vertical bar grouping, then it reads until it finds another newline, which terminates the line. None of the newlines between the vertical bars are considered line breaks and READWORD outputs all of the text as a single word. The output also includes the vertical bars.
A simple example:
SHOW READWORD Hello how are you?Hello how are you?
The following example shows how vertical bars are processed and preserved. Notice that READWORD outputs all of the text as a single word.
SHOW READWORD This is a line | WITH ONE VERTICAL BAR THIS IS NOW WITHIN A VERTICAL BAR THE END | some more text | BACK IN VERTICAL BAR THIS | ends it.This is a line | WITH ONE VERTICAL BAR THIS IS NOW WITHIN A VERTICAL BAR THE END | some more text | BACK IN VERTICAL BAR THIS | ends it.