Skip to content

General Nest syntax#

Comments#

In Nest there are two kinds of comments: line comments and block comments. Line comments start with -- and end at the end of the line. If there is a backslash at the end, the line feed is escaped and the line comment continues to the next line.

Block comments start with -/ and end with /-

-- This is a single line comment
-- This is another single line comment \
   that has the line-feed escaped

-/ this is a block comment which
   spans multiple lines without
   any escapes /-

File arguments#

In the command line there are some arguments that change the way a Nest file is compiled and interpreted. You can add some of those argument specifying them on the first line of the file. The line must start with --$ and then you can have any combination of the following space-separated arguments:

  • -O0 through -O3 to specify the optimization level of the file; if the specified level is higher than the one specified by the actual command, the latter is used
  • --encoding=<name> forces the file to be read with the given encoding, the list of valid encodings can be found here
  • --no-default will not add any predefined variable to the global scope except for _vars_

In this example the file will be read using CP1252, only simple expressions are optimized and no predefined variables are added.

--$ --no-default --encoding=cp1252 -O1

Note

any invalid argument is ignored and when specifying various optimization levels only the last one is considered

Value literals#

Numeric literals#

Integer literals can be decimal, binary, octal or hexadecimal. The first one has no prefix, the second 0b, the third 0o and the fourth 0x.

Binary and octal literals cannot be directly followed by another integer and hexadecimal literals cannot be followed by a word.

Real number literals support scientific notation but must always have some digits both before and after the decimal point.

Both integer and real literals can be prefixed with a minus - to make them negative. There can also be a plus sign + before the number but that does not change its sign.

-- Integer literals
10
-123
012 -- equal to 12 but still valid
+11
0b101
0o377
0xab

0b102 -- invalid because followed by 2
0o159 -- invalid because followed by 9
0xabg -- invalid because followed by g

-- Real literals
0.2
-13.4
1.0
+38.1
1.2e10
1.2e-10
1. -- invalid
.3 -- also invalid
3e10 -- invalid because real literals must always contain the decimal point

Nest has also a byte type that can be written as an integer literal followed by a lowercase b or an uppercase one B. If the integer is written with an hexadecimal literal, since adding a b at the end would be counted as digit, you start with 0h instead.

-- Byte literals
10b
256b -- equivalent to 0b
0b101b
0o123b
0hff

Decimal, binary and octal byte literals can be followed by a word or by another literal but that could cause confusion, so it is better to keep a space.

10bab -- split into '10b' and 'ab'
0b0b0 -- split into '0b' (from '0b0b') and '0'
00b10 -- split into '0b' (from '00b') and '10'

-- these are much clearer
10b ab
0b0b 0
00b 10

String literals#

String literals begin and end with either single or double quotes but there is a difference between the two: strings with double quotes can span multiple lines.

To escape a character you can use a backslash \ before the character and here are all the valid escape sequences:

Sequence Hex Value Name
\\ 5c Backslash
\' 27 Single quote
\" 22 Double quotes
\a 07 Alert / Bell
\b 08 Backspace
\e 1b Backspace
\f 0c Form feed / Page break
\n 0a Line feed / Newline
\r 0d Carriage return
\t 09 Horizontal tab
\v 0b Vertical tab
\xhh - Hexadecimal byte
\ooo - Octal byte
\uhhhh - Any BMP Unicode character
\Uhhhhhh - Any Unicode character
\(...) - A Nest expression

Note

h represents a hexadecimal byte (0-9, a-f or A-F) and o an octal one (0-7)

Note

Octal escapes can have either one, two or three digits: \0, \12 and \012 are all valid

Note

... are to be substituted with the expression to evaluate

Array literals#

Array literals start and end with curly braces ({ and }) and contain various expressions separated by a comma.

{1, 2, 3, 4}

Note

writing {} creates an empty map, not an empty array. To create an empty array you can write {,}

You can also create an array with all of the same value like this:

{10;30} --> array of length 30, with all values that are 10

This puts the same object in all slots of the array meaning that if an object can change values inside of itself (array, vector or map) the values of all objects will change:

{{1, 2};2} = a --> 'a' is equal to {{1, 2}, {1, 2}}
3 = a.0 .0 --> 'a' is now equal to {{3, 2}, {3, 2}}

Vector literals#

Vector literals start with <{ and end with }> and inside have various expressions separated by a comma.

<{1, 2, 3, 4}>

Just like arrays, vectors also have a smaller syntax to fill all slots with the same value:

<{10;30}> --> vector of length 30, with all values that are 10

Map literals#

Map literals start with { and end with } and inside have key-value pairs.

{'key_1': 1, 'key_2': 2}

The keys can be of type Str, Int or Byte since only these three types are hashable. Real objects cannot be hashed because of floating point error.

Anonymous functions (lambdas)#

Lambdas are declared by using ## followed by any number of identifiers that are the names of the parameters.

A lambda can return the value of a single expression by following the parameters with => or contain multiple statements with a block of code, delimited by [ and ].

##a b => a b + --> this lambda adds 'a' and 'b', returning their value

-- This lambda also prints the operation
##a b [
    >>> (a ' + ' b '\n' ><)
    => a b +
]

See also function declarations and the return statement.

Predefined variables#

  • Int: integer type
  • Real: real number type
  • Bool: boolean type
  • Null: null type
  • Str: string type
  • Array: array type, non-resizable ordered collection of objects
  • Vector: vector type, resizable ordered collection of objects
  • Map: hash map type, holds key-value pairs
  • Func: function type
  • Iter: iterator type
  • Byte: byte type, an integer from 0 to 255
  • IOFile: file type, similar to FILE * in C
  • Type: type of all types
  • true: boolean true
  • false: boolean false
  • null: the only possible value of type Null
  • _cwd_: a string showing the current working directory
  • _args_: an array with the arguments passed in the command line
  • _vars_: a table containing the variables of the local scope
  • _globals_: a table containing the variables of the global scope

Note

the value of _globals_ in the global scope is null

Expressions#

Stack operators#

An expression in Nest works in a similar way as it does in Lisp, where there are some operators which can operate with an indeterminate number of operands; these are called stack operators.

The stack operators in Nest are:

  • + addition
  • - subtraction
  • * multiplication
  • / division
  • ^ exponentiation
  • % modulus
  • >< concatenation
  • && logical and
  • || logical or
  • &| logical xor
  • & bit-wise and
  • | bit-wise or
  • ^^ bit-wise xor
  • << bit-wise left shift
  • >> bit-wise right shift
  • > greater than
  • >= greater than or equal to
  • < less than
  • <= less than or equal to
  • == equal to
  • != not equal to
  • <.> contains

To perform an operation with these operators you can write all the operands followed by the operator:

1 2 3 +
2 8 ^

To prioritize certain operations or to limit the number of operands of an operator, you can use parenthesis:

(3 2 ^) (4 2 ^) + 0.5 ^

this expression is equal to the python expression (3**2 + 4**2) ** 0.5.

The comparison operators (<, <=, >, >=, == and !=) operate in a different way though. They check each pair of adjacent operands and then check all the results to see if they are all true.

The following two expressions are equal but the first one is more concise:

1 2 3 4 <
(1 2 <) (2 3 <) (3 4 <) &&

Note

In the expression above, the values 2 and 3 are not actually evaluated twice. If you had for example a function such as #f [>>> 'hi\n'[] => 2] and used it inside the expression 1 @@f 2 <, hi would be only printed once.

Note

Writing a b c != does not mean that all three values are different from each other, it only means that adjacent ones are.

The operators +, -, * and / have a different meaning when operating in vectors.

The + operator appends any value to the end of a vector and returns the vector itself.

The - operator removes the first occurrence of a value in a vector and returns the vector itself.

The * operator repeats the contents of a vector a number of times and returns the vector itself.

The / operator pops a number of values from the end and returns the last value popped.

>>> (<{1, 2, 3}> 2 + '\n' ><) --> <{1, 2, 3, 2}>
>>> (<{1, 2, 3}> 2 - '\n' ><) --> <{1, 3}>
>>> (<{1, 2, 3}> 2 * '\n' ><) --> <{1, 2, 3, 1, 2, 3}>
>>> (<{1, 2, 3}> 2 / '\n' ><) --> 2

The operator - behaves differently with maps too. It will remove a key from a map and return the map itself.

{'a': 1, 'b': 2} = m
>>> (m 'a' - '\n' ><) --> {'b': 2}
>>> (m 'j' - '\n' ><) --> {'b': 2} removing a key that does not exist does not
                      --             throw an error

Local operators#

In Nest there is another type of operator that is called local operator. A local operator only operates with the operand on the right.

The local operators in Nest are:

  • $ length of an object
  • ! logical not
  • ~ bit-wise not
  • >>> write to the standard output
  • <<< write to the standard output and read from the standard input
  • -: negate
  • ?:: type of
  • @@ local call, calls a function with no arguments
  • |#| import

To operate with these operators you can write the operator followed by its operand:

>>> 'Hello, world!\n'

This kind of operators have the highest precedence, this means that writing >>> 'Hello ' name '!\n' >< will be executed as (>>> 'Hello ') name '!\n' ><, to change the order you can use parenthesis: >>> ('Hello ' name '!\n' ><)

Local-stack operators#

This third type of operator in Nest can take a set number of arguments, depending on the operator you are using. These operators are used do to specific functions built in the language.

The local-stack operators are:

  • :: casts an object to another type
  • @ calls a function
  • *@ calls a function with an array or a vector containing the arguments
  • -> creates an integer iterator
  • !! throws an error

To use a local-stack operator you write the last argument to the right and all the others to the left.

:: only takes two arguments: the object to cast and the type to cast it to.

Here the number 10 is casted to a Byte object:

Byte :: 10

The valid type casts in Nest are the following:

↱ Int Real Bool Null Str Array Vector Map Func Iter Byte IOFile Type
Int ✓ ✓ ✓ ✓ ✓
Real ✓ ✓ ✓ ✓ ✓
Bool ✓ ✓
Null ✓ ✓ ✓
Str ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Array ✓ ✓ ✓ ✓ ✓ ✓
Vector ✓ ✓ ✓ ✓ ✓ ✓
Map ✓ ✓ ✓ ✓ ✓ ✓
Func ✓ ✓ ✓
Iter ✓ ✓ ✓ ✓ ✓ ✓
Byte ✓ ✓ ✓ ✓ ✓
IOFile ✓ ✓ ✓
Type ✓ ✓ ✓

When Int, Real or Byte objects are casted to Bool, they become false if they are zero and true otherwise. When Str, Array, Vector or Map objects are casted to a boolean, it returns false if their length zero and true otherwise. When an IOFile is casted to Bool, it returns true if the file is open and false if it has been closed. When Null is casted to Bool, it always returns false. When any other object is casted to a Bool, it always returns true.

@ takes the number of arguments of the function plus the function itself as the last argument.

Here the function func is called with three arguments:

1 2 3 @func

*@ calls a function as well but you can have the arguments inside a vector or an array:

{1, 2, 3} *@func

Both for @ and *@, if there are less arguments than the function expected, to the remaining ones is passed null.

-> takes two or three arguments, the first argument is optional and is the step, the second is where the range should start, and the last is where the range should end.

This creates a range of even numbers from 10 (included) to 20 (excluded):

2 10 -> 20

!! takes two arguments, like ::. The first one is the name of the error and the last one the message that is printed along with the error.

Here is what would be printed when using this operator in example.nest.

'This Is The Name' !! 'this is the message'

Output:

> nest example.nest

File "example.nest" at line 1:
 1 | 'This Is The Name' !! 'this is the message'
This Is The Name - this is the message

If expression#

The syntax of the if expression is the following:

condition ?
    -- condition is true
:
    -- condition is false

The result of the if expression is the result of the expression evaluated, so a b == ? 2 : 3 means that if a and b are equal, the expression evaluates to 2 and to 3 otherwise. When there is no 'else' clause, the expression evaluates to null.

If you want to execute multiple expressions or statements you can use brackets:

a b == ? [
    -- code block here
] : [
    -- other code block here
]

When using a code block the expression evaluates to null:

(true ? [ true ] : false) = val

Here val is set to null because true is inside a block.

Assignment expressions#

An assignment expression assigns a value to a variable or changes a value in a vector, map or array.

To write an assignment expression you write the value, followed by an equal sign (=) or a compound equal sign (+=, -= or any stack operator which is not a comparison operator) and end with the name of the variable or an access to an element in an array, vector or map.

10 = a -- assigns the value 10 to the variable 'a'
3 -= a -- decrements 'a' by 3, now it is 7

There is another kind of assignment in Nest: the unpacking assignment. An unpacking assignment takes a vector or an array and splits its contents into the variables.

{1, 2} = {a, b} --> now 'a' is 1 and 'b' is 2

It can also be nested:

{1, {2, 3}} = {a, {b, c}} --> now 'a' is 1, 'b' is 2 and 'c' is 3

And can be used in for-as loops:

|#| 'stditutil.nest' = itu
{'a', 'b', 'c'} = arr

... arr @itu.enumerate := {idx, ch} [
    >>> (idx ' ' ch '\n' ><)
]

This program outputs:

1 a
2 b
3 c

Note

when using this assignment you cannot use compound assignments.

Access operator#

The access operator . can be used to get a specific value from vectors, arrays, strings and maps.

To access a value you write the value to access from, a dot, and the index of the value to get.

To index arrays, vectors or strings you can use integers. The first element is at index 0, the second at index 1 etc. until n - 1 where n is the length of the array or vector.

You can use also negative integers where -1 is the last element, -2 is the second to last element etc.

{1, 2, 3} = arr
arr.0 --> 1
arr. -1 --> 3

If you need to index based on a variable you must use parenthesis otherwise the variable name is treated like a string.

{1, 2, 3} = arr
2 = idx

arr.idx --> ERROR: arr.idx is equal to arr.'idx'
arr.(idx) --> 3

To index multiple-dimension arrays or vectors you cannot chain multiple extractions since a real number literal would be formed. To prevent this you can either put parenthesis around the integer or put a space before the dot.

{{1, 2},
 {3, 4}} = arr

arr.(0).(1) --> 2
arr.1 .1 --> 4
arr.1.0 --> ERROR: cannot index an array with '1.0'

To index a map you put the key of the value after the dot. If a key is a string that is also a valid variable name you can put the name without any quotes.

{'key_1': 2, 'invalid var': 10} = map

map.key_1 --> 10
map.invalid var --> ERROR: will try to get map.'invalid'
map.'invalid var' --> 10

map.not_a_key --> null

Note

if you try to index a key that is not in the map the result will be null

Statements#

The for loop#

The for loop has the following syntax:

... times_to_repeat [
    -- code
]

The for loop only repeats a block of code a certain number of times, to use an iterator and assign a variable, use a for-as loop.

The for-as loop#

The for-as loop has the following syntax:

... iterator := var_name [
    -- code
]

iterator is an expression that evaluates to an iterator and var_name is the variable to be assigned.

This for loop prints the numbers one through ten:

... 1 -> 11 := i [
    >>> (i '\n' ><)
]

The while and do-while loops#

The while loop has the following syntax:

?.. condition [
    -- code
]

The do-while loop has the following syntax:

..? condition [
    -- code
]

The only difference between while and do-while loops is that do-while loops execute the code once before checking the condition.

Function declaration#

A function declaration is a hash followed by the name of the function and the name of its arguments:

#func_name arg1 arg2 arg3 [
    -- code
]

As with lambdas, functions can also contain only one expression and return its value:

#func_name arg1 arg2 => -/ expression /-

When calling a function the arguments are taken from left to right:

#print_args a b c [
    >>> (a ' ' b ' ' c '\n' ><)
]

1 2 3 @print_args --> outputs '1 2 3'

The return statement#

The return statement is introduced by => and exits early from a function returning the value of the expression that follows it. If it is not followed by an expression or there is no such statement in the function, null is returned.

The switch statement#

The switch statement has the following syntax:

|> expression [
    ? case_1 [
        -- code executed if expression is equal to case_1
    ]
    ? case_2 [
        -- code executed if expression is equal to case_2
    ]
    ? [
        -- code for the default case
    ]
]

If expression is not equal to any of the cases, the code for the default case is executed. If there is no default case, nothing happens. When the code for a case is executed, the switch statement ends. To have the same behaviour as C when the break keyword is omitted, you can use the .. keyword.

The following two codes are equivalent:

// C / C++
switch 10
{
case 5:
    printf("5");
case 10:
    printf("10");
default:
    printf("default");
}
-- Nest
|> 10 [
    ? 5 [
        >>> 5
        ..
    ]
    ? 10 [
        >>> 10
        ..
    ]
    ? [
        >>> 'default'
    ]
]

The try-catch statement#

The try-catch statement has the following syntax:

??
    -- try block
?! error_var
    -- catch block

If you want multiple statements you can use brackets:

?? [
    -- try block
] ?! error_var [
    -- catch block
]

When using a try-catch statement any error that occurs inside the try block will be caught in the catch block; you cannot catch only specific errors.

If an error occurs, it will be stored inside error_var as a map with two keys:

  • name: the name of the error
  • message: the message of the error

Note

you can call error_var with any valid variable name

If you want to also get the position and traceback of the error you can use the try function of the stderr library.