Build a Custom Graph-Based Agent — build_custom

Build a reusable agent by wiring user-defined node functions into a state graph. This is the public extension point for creating custom LLMAgentR workflows.

Usage

build_custom_agent(
  node_functions,
  entry_point,
  edges = list(),
  conditional_edges = list(),
  default_state = list(),
  checkpointer = NULL,
  output = c("agent", "mermaid", "both"),
  direction = c("TD", "LR"),
  subgraphs = NULL,
  style = TRUE
)

Arguments

node_functions: Named list of node functions. Each function takes `state` and returns a named list or [make_command()].
entry_point: Name of the start node (must exist in `node_functions`).
edges: Optional list of static edges. Each item can be: - a character vector of length 2: `c("from", "to")`, or - a list with `from` and `to`.
conditional_edges: Optional list where each item contains: - `from` (or `node_name`), - `condition` (or `condition_fun`), - `mapping` (or `mapping_list`) as a named list of label -> node.
default_state: Optional named list merged into `state` for missing keys.
checkpointer: Optional callback `function(state, current_node)` executed after each transition.
output: Output mode: - `"agent"` (default): return runnable agent function, - `"mermaid"`: return Mermaid text only, - `"both"`: return list with `run`, `graph`, and `mermaid`.
direction: Mermaid direction used when `output` includes Mermaid.
subgraphs: Optional named list of subgraph groups for Mermaid rendering.
style: Logical; include default Mermaid class styling.

Value

- If `output = "agent"`: a function that accepts `state` and returns final state. - If `output = "mermaid"`: Mermaid flowchart text. - If `output = "both"`: list with `run`, `graph`, and `mermaid`.

Examples

if (FALSE) { # \dontrun{
custom <- build_custom_agent(
  node_functions = list(
    start = function(state) make_command("classify"),
    classify = function(state) {
      if (grepl("weather", state$query, ignore.case = TRUE)) {
        make_command("weather")
      } else {
        make_command("general")
      }
    },
    weather = function(state) list(answer = "Routing to weather handler"),
    general = function(state) list(answer = "Routing to general handler")
  ),
  entry_point = "start",
  edges = list(c("weather", "__end__"), c("general", "__end__")),
  output = "both",
  subgraphs = list(
    Router = c("start", "classify"),
    Handlers = c("weather", "general")
  )
)

cat(custom$mermaid)
custom$run(list(query = "weather in Accra"))
} # }