rlang::enquo() helpers for eager evaluation and idempotence

enquo_helpers.R

# enquo() helpers for eager evaluation and idempotence

# wrap eager() around enquo() to evaluate the quosure immediately in the calling
# environment *if* it can do so without error, otherwise return the quosure
eager <- function(quo) {
  val <- try(eval_tidy(quo), silent = TRUE)
  if (inherits(val, "try-error")) {
    quo
  } else {
    val
  }
}

# wrap idemp() around enquo() to make the the defusing operation *idempotent*; 
# in other words, prevent enquo() from creating quosures inside quosures
idemp <- function(quo) {
  val <- try(eval_tidy(quo), silent = TRUE)
  if (is_quosure(val)) {
    val
  } else {
    quo
  }
}

# note that when you use eager(), there is no need to use idemp() with it 
# because eager() also serves to make the defusing operation idempotent

# examples:

# just enquo()
a <- function(x) {
  enquo(x)
}
b <- function(y) {
  a(enquo(y))
}
b(z)
## <quosure>
## expr: ^enquo(y)
## env:  0x7f899bb14478
z <- 1
b(z)
## <quosure>
## expr: ^enquo(y)
## env:  0x7f899bb14478
rm(z)

# eager(enquo())
a <- function(x) {
  eager(enquo(x))
}
b <- function(y) {
  a(eager(enquo(y)))
}
b(z)
## <quosure>
## expr: ^z
## env:  global
z <- 1
b(z)
## [1] 1
rm(z)

# idemp(enquo())
a <- function(x) {
  idemp(enquo(x))
}
b <- function(y) {
  a(idemp(enquo(y)))
}
b(z)
## <quosure>
## expr: ^z
## env:  global
z <- 1
b(z)
## <quosure>
## expr: ^z
## env:  global
rm(z)