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7.19 Line Breaks

When LUX reads input from a file, then it can read ahead as much as it wants to until it can figure out the meaning of something on the line. Therefore, LUX ignores line breaks (where you start a new line) unless the line break changes the value or meaning to LUX of something on the command line. Also, newlines are important to the ignore and resume commands (Ignoring Input). Newlines are not allowed in the middle of a name, such as those of variables (Variables), functions (Function Definition, subroutines (Subroutine Definition, and argument keywords (Argument Specification); in the middle of a literal text string (between quotes (' or "); Strings) or a number (Scalars); or in the middle of a reserved keyword such as if or repeat (Reserved Keywords). In all other places in LUX files, newlines are allowed. So, in a LUX file, it is OK to have T,SIN ( 5.3 on one line and ) on the next line to form a complete command.

When LUX reads input from the keyboard, then it assumes for the most part that the user intended to finish one or more complete statements when the user pressed the RET key. Only in certain cases where a statement always includes more statements does LUX conclude that the user wants to give more input on following lines. These cases are: after the start of a subr, func, block, begin, {, if, case, ncase, for, repeat, do, or while statement and the corresponding end of the statement (Statements). For these purposes, the start of the statement consists of the keyword listed before, plus the name of the subroutine, function, or blockroutine (for subr, func, or block, or the condition (for if). The "corresponding end" of the statement consists of the very end of the statement, or of the keywords until or while (for repeat and do).

At the keyboard, the if statement presents special problems, because it may or may not contain an else clause. If you specify an if statement at the keyboard without an else on the same line as the end of the then clause, then LUX assumes the statement has no else clause.

You can explicitly indicate that a newline should be ignored by typing a continuation character (a minus sign, -) as the very last character on the line. If a minus sign is found as the last character on a command line (including inside a comment), then the minus sign is removed, and the contents of the next line are appended to the previous one before the whole thing is sent to the parser. Such continuation characters are not required in files, but are useful when copying and pasting lines from a file to the command line.

Below are some examples of LUX statements that generate errors when entered from the keyboard. It is assumed that the RET key is pressed at the end of each line.





In the first example, it is an error not to specify a closing parenthesis on the same line as the opening one. In the second example, a closing quote was expected on the same line as the opening quote. In the third example, a function name should follow func on the same line. In the last example, the else should be on the same line as the end of the then clause: now LUX will execute the if statement without the else clause and then complain about the unexpected else at the start of the next line. Except for the string example, which modifies the value of the string, all of these examples would not cause problems if they were read from a file.

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