Daniel A.A. Pelsmaeker Virtlink

Origin Tracking

Origin tracking is the idea to build an origin relation between input and output terms of a transformation in a term transformation system (TRS). It was first proposed by Van Deursen et al. in 1993 in the eponymous article. The origin relation can be used to traverse from a result term, to the term before the final transformation happened. This relation can be followed further, all the way back to the original input term before all transformations. Examples of uses for this relation (from the paper) are: constructing language-specific debuggers, visualising program execution, and associating positional information with messages in error reports. The first two examples relate to using the TRS to implement evaluation (interpretation) of a programming language, where the abstract syntax tree (AST) of a program is a term that is transformed to execute it. The origin relation allows a debugger or visualiser to show the execution one step at a time. The third example uses the origin relation tran

	#!/usr/bin/env bash
	set -o errexit
	set -o pipefail
	set -o noclobber
	set -o nounset
	#set -o xtrace #debug

	# ...

	# See: https://gist.github.com/Virtlink/b713707ede3f74bee2d902cf18f8d110

	# Make settings
	SHELL := /usr/bin/bash
	.SHELLFLAGS := -eu -o pipefail -c
	.DEFAULT_GOAL := help
	.ONESHELL:
	.DELETE_ON_ERROR:
	.SILENT:
	MAKEFLAGS += --no-print-directory