Construct a Custom ggpaintr Placeholder

Build one placeholder specification for use with ptr_merge_placeholders(). Custom placeholders can define their own UI control, runtime expression replacement, deferred UI binding, and evaluation-environment preparation.

Usage

ptr_define_placeholder(
  keyword,
  build_ui,
  resolve_expr,
  resolve_input = NULL,
  bind_ui = NULL,
  prepare_eval_env = NULL,
  copy_defaults = list(label = "Enter a value for {param}")
)

Arguments

keyword

A single syntactic placeholder name used inside the formula.

build_ui

Function with signature (id, copy, meta, context) returning a Shiny UI control or placeholder.

resolve_expr

Function with signature (value, meta, context) returning an R expression or ptr_missing_expr().

resolve_input

Optional function with signature (input, id, meta, context) returning the raw value to hand to resolve_expr(). Defaults to input[[id]].

bind_ui

Optional function with signature (input, output, metas, context) for registering deferred UI such as the built-in var placeholder.

prepare_eval_env

Optional function with signature (input, metas, eval_env, context) returning an updated evaluation environment.

copy_defaults

Optional named list with label, help, placeholder, and empty_text. Defaults to list(label = "Enter a value for {param}").

Value

An object of class ptr_define_placeholder.

Examples

date_placeholder <- ptr_define_placeholder(
  keyword = "date",
  build_ui = function(id, copy, meta, context) {
    shiny::dateInput(id, copy$label)
  },
  resolve_expr = function(value, meta, context) {
    if (is.null(value) || identical(value, "")) {
      return(ptr_missing_expr())
    }

    rlang::expr(as.Date(!!value))
  },
  copy_defaults = list(label = "Choose a date for {param}")
)
date_placeholder$keyword
#> [1] "date"