Reindent some lines of code

Using some fairly unsophisticated metrics, reindent() will take some lines of code and, according to its understanding of the rules for that language, reindent those lines. This is intended to help prettify automatically generated code.

This function is experimental.

Usage

reindent(lines, rules, tab = "    ", start = 0L)

Arguments

lines

Character vector with lines of text; can have internal newlines.

rules

Which rules to follow. You can pass a string from among "C", "C++", "Lua", or "R", or a list with elements:

• indent_more Character vector of tokens which increase the indent level.

• indent_less Character vector of tokens which decrease the indent level.

• indent_both Character vector of tokens which decrease, then increase the indent level (see Details).

• ignore Comment and string literal delimiters (see Details).

tab

Character string; what to use as an indent.

start

Indent level to start at.

Value

Reindented lines as a character vector.

Details

Conceptually, the function first ignores any comments or string literals. Then, line by line, reindent looks for tokens that signal either an increase in the indent level, a decrease in the indent level, or both at the same time. For example, in this Lua code:

if x == 1 then
    print 'one'
else
    print 'not one'
end

the if keyword increases the indent level, the else keyword both decreases and increases the indent level, and the end keyword decreases the indent level.

If provided, the ignore element of rules should be a list of character vectors. A character vector of length one is assumed to start a comment that runs to the end of the line (e.g. "#" in R). If length two, the two symbols are assumed to start and end a comment or string (e.g. "/*" and "*/" in C). If length three, then the first two symbols are start and end delimiters of a comment or string, while the third symbol is an "escape" character that escapes the end delimiter (and can also escape itself). This is typically a backslash.

reindent() supports "raw strings" in R, C, C++, and Lua code but only in limited cases. In R, when using raw character constants you must use an uppercase R, the double quote symbol and zero to two hyphens. In C/C++, when using raw string literals you must use the prefix R, and zero to two hyphens as the delimiter char sequence (plus parentheses). In Lua, you can use long brackets with zero to two equals signs. Any other attempt to use raw strings will probably break reindent().

Other unusual character sequences may also break reindent().

Examples

reindent(
    c(
        "if x == 1 then",
        "print 'one'",
        "else",
        "print 'not one'",
        "end"
    ),
    rules = "Lua")
#> [1] "if x == 1 then"      "    print 'one'"     "else"               
#> [4] "    print 'not one'" "end"