Multi-line Strings

DEP #:	8
Type:	Standards Track
Affects-DRM:	Yes
Author:	Carl Gay
Status:	Withdrawn (superseded by DEP 12)
Created:	16-Feb-2015
Last-Modified:	16-Feb-2015
Post-History:	16-Feb-2015 hackers@lists.opendylan.org
Target-Version:	2015.2

Abstract

Dylan currently has no way to encode multi-line strings into a single source token that crosses multiple source lines. This DEP proposes a literal syntax for multi-line strings.

Rationale

While it should be noted that encoding long string literals into source code is not good practice when internationalization is desired, it is convenient to have this ability for quick scripts and especially for encoding test data. Most modern programming languages provide this ability.

For very short multi-line strings one can get away with using \n or \r\n in a regular string:

"line one\nline two"

but readability quickly suffers as these strings get longer. An alternative is to put one string on each line and rely on automatic string concatenation by the compiler:

"line one\n"
"line two"

The problem here is that changing the contents of the string quickly becomes an editing chore as you attempt to keep the lines similar length and remember to put the \n at the end. Having a multi-line string literal syntax would alleviate both of these problems.

Specification

Multi-line string literals are delimited by three double quote characters on each end. The BNF, which augments the Character and String Literals section in the DRM, is

MULTI-LINE-STRING:

    """ more-multi-line-string

MORE-MULTI-LINE-STRING:

    multi-line-string-character more-multi-line-string

    """

MULTI-LINE-STRING-CHARACTER:

    any printing character (including space) except for \\

    \\ escape-character

Escape characters are interpreted as with the standard STRING production. Literal end-of-line sequences (\n and \r\n) are always interpreted as a single newline character, regardless of operating system platform.

Examples:

Equivalent to "abc":

"""abc"""

Equivalent to "line one\nline two":

"""line one
line two"""

Equivalent to "let x = \"foo\";":

"""let x = "foo";"""

Equivalent to "\nfoo\nbar\n":

"""
foo
bar
"""

Reference Implementation

A reference implementation can be found on github. As of this writing, the implementation is functional but needs a few internal cleanups.

Open Issues

This proposal currently has no provision for string literals in which there is no escape sequence interpretation, i.e. “raw” strings.

Revision History

The revision history of this document is available here: https://github.com/dylan-lang/opendylan/commits/master/documentation/source/proposals/dep-0008-multi-line-strings.rst