cat_re: Print a regular expression to the console
In wai-wong-reimagine/mclm: Mastering Corpus Linguistics Methods

Description Usage Arguments Details Value See Also Examples

The function cat_re prints a regular expression to the console. By default, the regular expression is not printed as an R string, but as a ‘plain regular expression’. More specifically, the regular expression is printed without surrounding quotation marks, and characters that are special characters in R strings (such as quotation marks and backslashes) are not escaped with a backslash. Also, by default, multi-line regular expressions are printed as single-line regular expressions with all regular expression comments removed.

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cat_re(x,
       format = c("plain", "R", "TeX"),
       as_single_line = TRUE)

`x`	a character vector containing a regular expression. If the length of `x` is higher than 1, then only `x[1]` is taken into account.
`format`	a character vector describing the requested output format. If the length of `format` is higher than 1, then only `format[1]` is taken into account.
`as_single_line`	a boolean vector specifying whether the regular expression should be converted to a single-line regular expression (which also implies removing all regular expression comments) prior to printing. If the length of `as_single_line` is higher than 1, then only `as_single_line[1]` is taken into account.

In the current implementation, the way the character \# is handled is not guaranteed to be correct. More specifically, the code is not guaranteed to correctly distinguish between a \# symbol that introduces a regular expression comment and a \# symbol that doesn't do so. Firstly, there is no testing whether at the point of encountering \# we're in free-spacing mode. Second, there is no thorough testing whether or not the \# symbol is part of a character class. However, \# is processed correctly as long as any ‘literal #’ is immediately preceded by either a backslash or an opening square bracked, and any ‘comment-introducing #’ is not immediately preceded by a backslash or an opening square bracket.

The (invisible) value of cat_re is the same as its first argument, viz. the character vector x.

See also scan_re.

# single-line regular expression
x <- "(?xi)  \\b \\w* willing \\w* \\b"
cat_re(x)

# multi-line regular expression
y <- "(?xi)  
       \\b        # word boundary 
       \\w*       # optional prefix
       willing   # stem
       \\w*       # optional suffix
       \\b        # word boundary"
cat_re(y)
cat_re(y, as_single_line = FALSE)
cat_re(y, format = "R")
cat_re(y, format = "R", as_single_line = FALSE)