chat_append_message: Low-level function to append a message to a chat control

In shinychat: Chat UI Component for 'shiny'

Low-level function to append a message to a chat control

Description

For advanced users who want to control the message chunking behavior. Most users should use chat_append() instead.

Usage

chat_append_message(
  id,
  msg,
  chunk = TRUE,
  operation = c("append", "replace"),
  session = getDefaultReactiveDomain()
)

Arguments

id	The ID of the chat element
msg	The message to append. Should be a named list with role and content fields. The role field should be either "user" or "assistant". The content field should be a string containing the message content, in Markdown format.
chunk	Whether msg is just a chunk of a message, and if so, what type. If FALSE, then msg is a complete message. If "start", then msg is the first chunk of a multi-chunk message. If "end", then msg is the last chunk of a multi-chunk message. If TRUE, then msg is an intermediate chunk of a multi-chunk message. Default is FALSE.
operation	The operation to perform on the message. If "append", then the new content is appended to the existing message content. If "replace", then the existing message content is replaced by the new content. Ignored if chunk is FALSE.
session	The Shiny session object

Value

Returns nothing (invisible(NULL)).

Examples

library(shiny)
library(coro)
library(bslib)
library(shinychat)

# Dumbest chatbot in the world: ignores user input and chooses
# a random, vague response.
fake_chatbot <- async_generator(function(id, input) {
  responses <- c(
    "What does that suggest to you?",
    "I see.",
    "I'm not sure I understand you fully.",
    "What do you think?",
    "Can you elaborate on that?",
    "Interesting question! Let's examine thi... **See more**"
  )

  # Use low-level chat_append_message() to temporarily set a progress message
  chat_append_message(id, list(role = "assistant", content = "_Thinking..._ "))
  await(async_sleep(1))
  # Clear the progress message
  chat_append_message(id, list(role = "assistant", content = ""), operation = "replace")

  for (chunk in strsplit(sample(responses, 1), "")[[1]]) {
    yield(chunk)
    await(async_sleep(0.02))
  }
})

ui <- page_fillable(
  chat_ui("chat", fill = TRUE)
)

server <- function(input, output, session) {
  observeEvent(input$chat_user_input, {
    response <- fake_chatbot("chat", input$chat_user_input)
    chat_append("chat", response)
  })
}

shinyApp(ui, server)

shinychat documentation built on June 10, 2025, 9:09 a.m.