interpolate: Evaluate expressions within strings.

In crowding/vadr: Macros, metaprogramming, and pleasant programming idioms.

Description

Interpolate evaluated expressions into strings.

Usage

interpolate(str, begin = ".(", end = ")", envir = arg_env(str,
  environment()))

interply(str, begin = ".(", end = ")", envir = arg_env(str,
  environment()))

str %#% args

Arguments

str	A template string. For interply, must have length 1.
begin	The beginning delimiter.
end	The ending delimiter.
envir	The environment evaluation takes place in. Defaults to the lexical environment of the template.
args	A list or named vector; interpolation happens in an environment with these values bound.

Details

For interpolate, the argument is scanned for substrings that look like ".(expr)". These are replaced by the evaluation of the expression. Expressions will be matched respecting the balancing of braces and quotes.

interply generates a function that performs this interpolation for a particular string. The interpolation is repeated along the arguments applied to the function (so the usage is interply(".(x),.(y)")(x=val, y=val), similar to mply and qqply.) Note unnamed arguments can be referred to as ..1, ..2, etc.

%#% is a shortcut for applying interpolation to data from a list or named vector. string %#% values is equivalent to interply(string) %()% values.

Value

A character vector.

Note

If accepting a formatting string from user data, it is prudent to specify emptyenv() or a descendant of emptyenv() populated only with "allowed" functions and data.

Author(s)

Peter Meilstrup

See Also

qq qqply mply

Examples

foo<-1; bar<-"two"; baz <- "III"
interpolate(c(".(foo),", "a .(bar)", "a .(foo) .(bar) .(baz)"))
interply("hello .(..1)")(c("world", "nurse", "kitty"))
interply("hello {{q}}", begin="{{", end="}}")(q=c("there", "you"))
"hello .(x)" %#% c(x="world")

#shell-style interpolation -- "$" start and no end delim
interply("$hello, ${paste(rep('hello', 3), collapse=' ')}, $'hi'",
         begin="$", end=""
         )(hello="hola")

# Compliant 99 Bottles implementation:
bottles <- interply(
  ".(ifelse(n%%100>0, n%%100, 'no more')) bottle.('s'[n%%100!=1]) of beer")
initcap <- function(x) {substr(x, 1, 1) <- toupper(substr(x, 1, 1)); x}
verse <- interply(
  paste0(".(initcap(bottles(n=n))) on the wall, .(bottles(n=n)).\n",
         ".(c('Go to the store and buy some more,',",
         "    'Take one down and pass it around,')[(n%%100!=0)+1])",
         " .(initcap(bottles(n=n-1))) on the wall."))
cat(verse(n=99:0), sep="\n\n")

crowding/vadr documentation built on May 14, 2019, 11:33 a.m.