Differences between SETL implementations

From the SETL Wiki

There are some subtle differences between the various implementations of SETL, that are likely to confuse a programmer attempting to port code from one implementation to another. This page is an incomplete list of such differences. If you discover more please add them!

Implementation-specific features (e.g. language extensions, extra built-in functions) are covered elsewhere.

Contents 1 Syntactic differences 1.1 Strings 1.2 Procedures 1.3 from and similar operators 2 Types 2.1 Sets 3 Primitives 3.1 Overloading of primitives 3.2 Redefinition of primitives 4 Run-time behavioural differences

[edit] Syntactic differences

Starting with the obvious ones...

[edit] Strings

In CIMS SETL and SETL-S, string literals are enclosed in single quotes, e.g. 'Hello, World'.
In SETL2, string literals are enclosed in double quotes, e.g. "Hello, World!".
In GNU SETL, both are valid.

[edit] Procedures

• In SETL-S all procedure must be forward-declared at the beginning of a program. All other implementations make 2 or more passes through the source code and scan for procedure names on the first pass, thus they do not require these forward declarations.

• In CIMS SETL, SETL-S and GNU SETL, proc is a synonym for procedure. In SETL2, it isn't.

[edit] from and similar operators

CIMS SETL and SETL2 allow an assignment using the from, fromb or frome operator to be used in an expression context, e.g.

t := [1, 2, 3];
print(x fromb t);
print(x);
print(t);

outputs:

1
1
[2 3]

SETL-S and GNU SETL do not permit this syntax.

[edit] Types

[edit] Sets

It is not normally possible to construct a set that has om as an element. For example "{om}" and "{} with om" both evaluate to the empty set. However in SETL2 the range operator can return a set containing om, if given a map containing a one-element tuple, e.g. "range({[1], [2, 3]})" yields {om, 3}.

[edit] Primitives

[edit] Overloading of primitives

• SETL2 permits the argument of arb to be a tuple. None of the other implementations permit anything other than a set.

[edit] Redefinition of primitives

In SETL2, most of SETL's unary operators are demoted to (predefined) procedures. These include all of the standard math functions, e.g. sin, abs, even etc. The built-in definitions can be overridden by the programmer defining a procedure of the same name. Exceptions are pow, not, arb, domain and range, which are still unary operators in SETL2.

[edit] Run-time behavioural differences

There are some slight differences in the implementations of some of the set primitives, regarding their behaviour when given om as an argument:

Operator / function	Expression	Results			Alternative
		SETL-S	SETL2	GNU SETL
{} (set former)	{om}	error	{}	{}	{e: e in [x]}
with	s with om	error	s	s	s with/ [x]
less	s less om	s	s	error	s less/ [x]
in	om in [1, om, 2]	error	true	true	(exists i in [1 .. #t] | t(i) = x)
	om in {}	error	false	false	x /= om and x in s

The "alternative" column above gives an expression which may be used instead if it is unknown whether x is om or not.