Syntax

Comments

Like in Lua, line comments start with -- and end at the end of the line.

-- this is a comment

Block comments start with -* and end with *-.

-* this is a block comment
spanning multiple
lines *-

Block comments cannot (currently) be nested.

Comments are ignored during compilation and do not appear in the compiled Lua code.

Keywords

Hurdy keywords

Hurdy reserves the following keywords

and as break continue else elseif false for
function from global if import in method nil
or return repeat true until var while

as well as _hurdytemp followed by a number (e.g., _hurdytemp1, _hurdytemp568)—these are used internally by the transpiler.

Reserved Hurdy keywords cannot be used a variable names, but can be used as keys to index objects:

for = 5 -- this is not allowed
x.for = 5 -- this is ok

Lua keywords

Lua keywords that are not Hurdy keywords are also reserved and cannot be used as identifiers (including to index objects):

do end local not then goto

local = 5 -- this is not allowed
x.local = 5 -- this is also not allowed

Identifiers

Identifiers in Hurdy are case-sensitive, start with a letter or underscore, and can contain letters, numbers, or onderscores. Only ASCII letters are allowed in identifiers.

Strings

Strings follow the same syntax as Lua (for both short and long strings).

"This is a short string"

[[ This is a level 0 long string ]]

[===[ This is a level 3 long string ]===]

The Hurdy compiler processes some of the Lua escape sequences during compilations (only inside short strings), allowing them to be used in versions of Lua that don’t support them.

\z escape sequence

The \z escape sequence ((introduced in Lua 5.2)) is processed during compilation to remove all following whitespace (including newlines), so the resulting code can be run on Lua 5.1:

"example \z


   of escape sequence"

is equivalent to

"example of escape sequence"

\x escape sequence

The hexadecimal escape sequence x (introduced in Lua 5.2) is processed during compilation to convert it to a decimal escape sequence representing the same byte, so the resulting code can be run on Lua 5.1:

"\xFF"

is equivalent to

"\255"

\u escape sequence

The UTF-8 escape sequence u (introduced in Lua 5.3) is processed during compilation to convert it to one or more decimal escape sequences representing the character code point, so the resulting code can be run on Lua 5.1 and 5.2:

"\u{a9}"

is equivalent to

"\194\169"

Newlines

Statements in Hurdy are sperated using newlines (\n). To allow for freedom of formatting and to split lines that are too long, newlines are ignored after a token that cannot end a statemet.

print(
  1, 2,
  3
)

and

print(1, 2, 3)

produce the same result.

Operators

All of Lua’s operators are supported and have the same precedence and associativity rules as in Lua, although in some cases (exponentiation, logical NOT, bitwise XOR, inequality) Hurdy uses a different symbol. Refer to the tables below for the correct symbols.

Additionally, Hurdy has extra assignment operators, such as addition assignment.

Arithmetic operators

Hurdy operator	Lua operator	Description	Notes
+	+	Addition
-	-	Subtraction
*	*	Multiplication
/	/	Float division
//	//	Floor division	Requires Lua 5.3+
%	%	Modulo
**	^	Exponentiation	Different than Lua
-	-	Unary minus

Logical operators

Hurdy operator	Lua operator	Description	Notes
and	and	Logical AND
or	or	Logical OR
!	not	Logical NOT	Different than Lua

Bitwise operators

Bitwise operators are supported, but the compiled code must be run with Lua 5.3+.

Hurdy operator	Lua operator	Description	Notes
&	&	Bitwise AND
|	|	Bitwise OR
^	~	Bitwise XOR	Different than Lua
>>	>>	Bitwise right shift
<<	<<	Bitwise left shift
~	~	Bitwise NOT

Relational operators

Hurdy operator	Lua operator	Description	Notes
==	==	Equality
!=	~=	Inequality	Different than Lua
<	<	Less than
>	>	Greater than
<=	<=	Less or equal
>=	>=	Greater or equal

Additional operators

Hurdy operator	Lua operator	Description
..	..	Concatenation
#	#	Length

Assignment operators

Hurdy operator	Lua operator	Description	Notes
=	=	Assignment
+=		Addition assignment
-=		Subtraction assignment
*=		Multiplication assignment
/=		Float division assignment
//=		Floor division assignment	Requires Lua 5.3+
and=		Logical AND assignment
or=		Logical OR assignment
&=		Bitwise AND assignment	Requires Lua 5.3+
|=		Bitwise OR assignment	Requires Lua 5.3+
^=		Bitwise XOR assignment	Requires Lua 5.3+
>>=		Bitwise right shift assignment	Requires Lua 5.3+
<<=		Bitwise left shift assignment	Requires Lua 5.3+

The regular assignment operator works just as in Lua, and in particular it can be used with multiple identifiers on the left and/or multiple values on the right:

x = 3
y = nil, 2

x, y = 3, 2

All the extra assignment operators which are unique to Hurdy associated to binary operators work in the same way, and can only be used with one identifier on the left and one variable on the right. For example for addition assignment

x += y

translates to the Lua code

x = x + y

Warning

Something to keep in mind when using assignment operators is that the left-hand-side is evaluated twice:

t.x += 2

-- equivalent to

t.x = t.x + 2 -- evaluated when adding and when assigning

This could lead to unwanted results if t.x is obtained through a __index metamethod on t.