Characters, Keywords, Identifiers

Characters

These are the characters used by ISETL:

@ [ ] ; : = | { } ( ) . # ? * / + - _ " < > % ~ , ' ^

a through z

A through Z

0 through 9

In addition, the following character-pairs are used.

:=   ..   **   /=   <=   >=   ->

In set builder notation the characters ":" and "|" may be used interchangably.

Example:

{x | x in {1..11} : odd(x)};

is the same as

{x | x in {1..11} | odd(x)};

is the same as

{x : x in {1..11} : odd(x)};

and means the set of all x such that x is an element of {1,2,3,4,5,6,7,8,9,10,11} such that x is odd.

Keywords

• and
• choose
• div
• do
• else
• elseif
• end
• exists
• false
• for
• forall
• from
• fromb
• frome
• func
• if
• iff
• impl
• in
• inter
• less
• local
• mod
• newat
• not
• notin
• of
• om (OM)
• opt
• or
• print
• printf
• proc
• program
• read
• readf
• return
• subset
• take
• then
• to
• true
• union
• value
• where
• while
• with
• write
• writeln

Identifiers

An identifier is a sequence of characters that are alphabetic, numeric, an underscore ("_"), an apostrophe ("'"), or a caret ("^"). It must begin with a letter. Upper or lower case alphabetic characters may be used, and ISETL is case-sensitive. (i.e. MID_POINT, Mid_Point, and mid_point are legal and are different.)

Examples:

Length length LENGTH is_associative remainder y y' y'' y2 X37	valid identifiers
is associative y" 2y	not valid: space not allowed in identifier not valid: prime prime (apostrophe apostrophe)is OK, but not double quote not valid: doesn't begin with an alphabetic character

An identifier serves as a variable and can take on a value of any ISETL data type. The type of a variable is entirely determined by the value that is assigned to it and changes when a value of a different type is assigned.