Section 2: Lexical Structure

This chapter will describe the lexical structure of Keli. Most of the information on this page can be ignored during the first reading of this report.

2.1 Notational Conventions

The following notations are used to described the grammar of Keli (for more info, lookup EBNF):

Notation	Meaning
[ pattern ]	optional
{ pattern }	repetition
( pattern )	grouping
pattern1 | pattern2	choice
pattern1	difference; elements of pattern1 except those of pattern2
hello	terminal syntax in typewriter font

2.2 Abbreviations

The following abbreviations will be used to describe the lexical structure of Keli.

Abbreviation	Meaning
id	identifier
op	operator
alnum	alphanumeric

2.3 Lexical Program Structure

Term	Definition
program	{ lexeme | whitespace }
lexeme	id | literal | reservedOp
id	alnumId | symbolicId
alnumId	( # | ? | _ | alphabet ) { alphabet | digit |# | ? | - | _}
operator	( ~ | ! | @ | $ | % | ^ | & | * | - | = | + | / | < | > | : | \ )
alphabet	a | ... |z | A | ... | Z
digit	0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
literal	integer | float | string
integer	decimal
float	decimal . decimal
decimal	digit { digit }
string	" { space | escape | gap } "
reservedOp	=
whitespace	whitestuff { whitestuff }
whitestuff	whitechar | comment
whitechar	newline | vertab | space | tab | unicodeWhitespace
newline	return linefeed | return | linefeed | formfeed
return	a carriage return
linefeed	a line feed
vertab	a vertical tab
formfeed	a form feed
space	a space
tab	horizontal tab
unicodeWhitespace	any Unicode character defined as whitespace
comment	slashes [ nonnewline { nonnewline }] newline
slashes	/ / { / }

2.4 Comments

Comments are actually whitespaces. Comments starts with 2 slahses and extends until before the following newline. For example:

// this is a comment

2.5 Constant Identifiers

A constant identifier is any sequences of characters that satisfy the following grammar:

( $ | _ | alphabet ) { alphabet | digit | - | _}

For example:

Term	Validity
hello	Valid
_	Valid
true	Valid
snake_case	Valid
aVariable	Valid
x123	Valid
crazy_stuff_lol	Valid
Content-Type	Valid
12x	Invalid

Constant identifiers are used for identifying:

1. Function parameter

2. Type

3. Object property

4. Type variable

2.6 Function identifiers

Function identifiers are used for identifying functions, they can be any sequences of characters that satisfy the following grammar:

constId | ({operator }) <reservedOp>

In layman term, a function identifier can be a constant identifiers OR a sequences of symbols that are not reserved operator.

Examples of function identifiers:

Term	Validity
plus	Valid
toString	Valid
+	Valid
->	Valid
==	Valid
=	Invalid, reserved operator