Relation:Instructions

A relation program is a sequence of instructions. Normally, each instruction is executed one after the other. Some instructions are global, others work on a stack of relations. In the latter case they are executed for each row in a relation.

Each instruction is on one line. It starts with a keyword and then may have options.

Global instructions

name	options	example
set	field = expression	set currentyear = 2020

Create relations

name	options	example
relation	columnlist	relation film, director, year
insert	expressionlist	insert "Home", "Ursula Meier", 2007
data	expressionlist	data Home, Ursula Meier, 2007 Beresina,Daniel Schmid,1998 end data
read	(encoding) filename	read "films.csv"
import	filename	import "rawtext.txt"

Output relations

name	options	example
echo	expression	echo "5 * 4 "
format	field format	format year "0"
label	label for header	label electeurs "électeurs"
print	(lines)	print
write	filename	write "films.csv"

Unary relational algebra

name	options	example
select	expression	select year > 2005
project	fieldlist	project title, year
rename	field newfield	rename title original_title
extend	field = expression	extend title2 = upper(title)

Binary relational algebra

name	options	example
join	expression	join natural
union	-	union
difference	-	difference
intersection	-	intersection

Not really relational algebra

name	options	example
order	field mode	order year 9
limit	start length	limit 125 25

Stack operators

name	options	example
dup	-	dup
pop	-	pop
swap	-	swap

Flow control

name	options	example
if	expression	if currentyear > 2005 beep end if
while	expression	set currentyear 2000 while currentyear < 2005 beep set currentyear currentyear + 1 end while

Substructures

name	options	example
function	paramerterlist	function double n set result 2 * n end function
program	paramerterlist	program prg n read "file".n."csv" end program
run	programname parameterlist	run prg 2020
transaction	-	transaction write "data.csv" assert unique id end transaction

Advanced functions

name	options	example
beep	(tones)	beep
assert	option expression	assert all year > 2005
compile	expression	compile 5+4
deserialize		deserialize
include	filename	include "header.rel"
parse	field regex fieldlist	parse line "(dd)s(dd)" year, month
serialize		serialize
template	filename	template "tmp.txt"
stack	-	stack