List of programming languages that require newlines

A oneliner is a computer program written in a single line, without using any newline (\n) characters. This is common in interactive shell scripting, which for practical reasons are only written as a single line, and languages such as Perl and APL have a culture of writing substantial pieces of logic as single lines.

Most languages whose syntax is based on standard tokenisation, where all forms of whitespace are treated similarly, allow us to replace any newline character with a space character, and thus let us write programs of any complexity on a single line. Even languages that use newline characters rather integrally, such as Python, may have escape hatch notation such as semicolons that allows us to avoid newlines in most or all cases.

The following lists attempts to catalogue programming languages that do not allow arbitrarily complicated programs to be written on a single line. Sometimes the reason is particularly subtle (or not even clear), which are of course the most interesting cases.

Some language specifications (remember when languages didn’t just have implementations?) allow implementations to impose limits on line lengths, which naturally puts a limit on the size of single line programs. We are ignoring those limits in the following, since it’s not terribly interesting.

Further, the POSIX standard defines a line as always ending in \n, even the last (or only) line in a file (POSIX 2017, section 3.206). This also precludes \n-free programming. We will leave it to the Unix philosophers whether a oneliner may have a single newline in it. Similarly, POSIX also allows lines to have a maximum length.

The list

• C and C++. Most of C’s syntax does not distinguish newlines from other kinds of whitespace. However, in order to perform any kind of I/O, you must #include header files, and an #include (or any other preprocessor directive) must be followed by a newline. Also, the C99 specification requires (in section 5.1.1.2/1) that a source file must end in a newline. This was changed in C11 to be implementation-defined.

• Fixed format FORTRAN. Old versions of FORTRAN had a very rigid line-oriented syntax (even the use of specific columns were meaningful), hailing from its punch card origins.

• Fixed format COBOL, similarly to FORTRAN.

• Makefiles use a line-based syntax where a newline character marks the end of a statement.

• Whitespace, as newlines are used for I/O and control flow.

The co-list

These languages may look like they require newlines, but actually do not, for reasons that are subtle and/or interesting.

• Python. Statements in Python are normally separated by newlines, but semicolons can be used to put multiple statements on the same line. Some built-in bits of syntax (such as control flow) do not allow this, but you can work around it with recursion. The import syntax also requires a newline, but you can import modules by directly calling functions instead. This will certainly not look like very idiomatic Python.

• Elixir provides a lot of syntactic sugar with delimited blocks that requires newline characters, but it desugars to method calls and anonymous functions, which you could in principle write directly.

• Haskell is usually written with syntactically significant whitespace, including newlines, but this is in fact syntactic sugar over an explicit syntax defined in terms of semicolons and curly braces. Even if this was not the case, Haskell actually allows formfeeds and carriage returns in lieu of \n.