Turtle.Line

A line of text (does not contain newlines).

Convert a line to a text value.

Split text into lines. The inverse of linesToText.

Merge lines into a single text value.

Try to convert a text value into a line. Precondition (checked): the argument does not contain newlines.

Convert a text value into a line. Precondition (unchecked): the argument does not contain newlines.

The NewlineForbidden exception is thrown when you construct a Line using an overloaded string literal or by calling fromString explicitly and the supplied string contains newlines. This is a programming error to do so: if you aren't sure that the input string is newline-free, do not rely on the IsString Line instance.

When debugging, it might be useful to look for implicit invocations of fromString for Line:

>>> sh (do { line <- "Hello\nWorld"; echo line })
*** Exception: NewlineForbidden

In the above example, echo expects its argument to be a Line, thus line :: Line. Since we bind line in Shell, the string literal "Hello\nWorld" has type Shell Line. The IsString (Shell Line) instance delegates the construction of a Line to the IsString Line instance, where the exception is thrown.

To fix the problem, use textToLines:

>>> sh (do { line <- select (textToLines "Hello\nWorld"); echo line })
Hello
World