Set function parameters within the global environment. Useful for debugging R functions.

setFunctionParams.R

#' Set function parameters for debugging.
#' 
#' Sets the defauls for the parameters in the given function witin an environment.
#' 
#' @param fun the function whose parameters should be set.
#' @param envir the environment to set those parameters.
#' @param missing.value value to assign to parameters that do not have a defautl value.
#' @param overwrite should parameters already defined be overwritten.
setFunctionParams <- function(fun, 
  						  envir=.GlobalEnv,
							  missing.value,
							  overwrite=FALSE) {
	setValue <- function(name, value, missing.value=missing.value) {
		if(nchar(name) > 0 & !missing(value)) {
			if(!overwrite & exists(x=name, envir=envir)) {
				message(paste0('Value for ', name, ' already defined in the environment'))
			} else {
				tryCatch( {
					message(paste0('Setting ', name, ' = ', eval(value)))
					assign(name, eval(value), envir)
				}, error=function(e) { 
					warning(paste0('Cannot set value for ', name))
					return(FALSE)
				})
			}
		} else if(missing(value) & name != '...') {
			if(!missing(missing.value)) {
				message(paste0('No value defined for ', name, 
							   '. Setting to ', missing.value))
				assign(name, value, envir=envir)
			} else {
				message(paste0('No value defined for ', name, '.'))
			}
		}
		return(TRUE)
	}
	
	fun.list <- as.list(fun)
	revisit <- integer()
	for(i in seq_along(fun.list)) {
		name <- names(fun.list)[i]
		value <- fun.list[[i]]
		if(!setValue(name, value)) { revisit <- c(revisit, i) }
	}
	for(i in revisit) { 
		# We will try a second time in case an earlier parameter relies on the
		# value of a later value. This may still not work all the time if there
		# is a more complex interrelationship among the parameters.
		name <- names(fun.list)[i]
		value <- fun.list[[i]]
		setValue(name, value)
	}
}