Runtime Options

Arl behavior is controlled by a combination of R options and environment variables. Every user-facing setting can be configured through either mechanism.

Precedence

When both an R option and an environment variable are set for the same setting, the R option wins:

  1. R option (options(arl.foo = value)) – highest priority
  2. Environment variable (ARL_FOO=value) – fallback
  3. Built-in default – used when neither is set

The naming convention is straightforward: option arl.foo_bar maps to environment variable ARL_FOO_BAR.

Setting values

From R:

# R option (takes effect immediately, session-scoped)
options(arl.repl_quiet = TRUE)

# Environment variable (inherited by child processes)
Sys.setenv(ARL_REPL_QUIET = "1")

From the shell:

# Before starting R or the arl CLI
export ARL_REPL_QUIET=1

For boolean settings, the environment variable values 1, true, and yes (case-insensitive) are treated as TRUE; anything else is FALSE.

User-facing settings

Setting R option Env var Default Description
Suppress display/trace arl.quiet ARL_QUIET FALSE Silence display and trace output
REPL quiet/banner arl.repl_quiet ARL_REPL_QUIET FALSE Start REPL without the startup banner
REPL history arl.repl_use_history ARL_REPL_USE_HISTORY TRUE Enable REPL command history
REPL bracketed paste arl.repl_bracketed_paste ARL_REPL_BRACKETED_PASTE TRUE Enable bracketed-paste mode in the REPL
CLI quiet (errors) arl.cli_quiet ARL_CLI_QUIET FALSE Suppress CLI error messages and help text
Macro debug output arl.debug_macro ARL_DEBUG_MACRO FALSE Print debug info during macro expansion
Disable self-TCO arl.disable_tco ARL_DISABLE_TCO FALSE Disable self-tail-call optimization (for debugging)
Disable constant folding arl.disable_constant_folding ARL_DISABLE_CONSTANT_FOLDING FALSE Disable compile-time constant folding (for testing)
Disable all optimizations arl.disable_optimizations ARL_DISABLE_OPTIMIZATIONS FALSE Disable all non-essential compiler optimizations at once
Display line limit arl.display.max.lines ARL_DISPLAY_MAX_LINES 20 Max lines for S3 object display (Inf to disable)

Shell-only settings

Some settings are checked in the shell wrapper before R starts, so they can only be set as environment variables:

Env var Description
ARL_SKIP_USER_PROFILE Skip sourcing ~/.Rprofile when launching the CLI

Examples

Suppress all display and trace output:

options(arl.quiet = TRUE)
engine <- arl::Engine$new()
engine$eval_text('(display "this is silent")')  # no output

Or equivalently via environment variable:

Sys.setenv(ARL_QUIET = "1")
engine <- arl::Engine$new()
engine$eval_text('(display "this is silent")')  # no output
Sys.unsetenv("ARL_QUIET")

Start the REPL without a banner:

options(arl.repl_quiet = TRUE)
# or: Sys.setenv(ARL_REPL_QUIET = "1")

Internal settings

The following options are used internally for testing or session state. They do not have environment variable equivalents and are not intended for end-user configuration:

  • arl.env_cache_warning_shown – session flag for one-time cache warning
  • arl.coverage_tracker – active CoverageTracker R6 object
  • arl.stdin – override R connection for stdin
  • arl.repl_read_form_override – test hook for REPL input
  • arl.repl_can_use_history_override – test hook for history detection
  • arl.cli_exit_fn – test hook for CLI exit behavior
  • arl.cli_isatty_override – test hook for TTY detection
  • arl.cli_read_stdin_override – test hook for stdin reads