# Elements

Ontology asks, What exists?,
to which the answer is Everything.
— W.V.O. Quine, Word and Object

Line comment

q)/Oh what a lovely day

Trailing comment
q)2+2  /I know this one
4

Multiline comment
/
Oh what a beautiful morning
Oh what a wonderful day
\
a:42
\
ignore this and what follows
the restroom at the end of the universe


## Nouns¶

noun examples
atom 42; "a"; 1b; 2012.08.04; ibm
vector (43;44;45); "abc"; 0101b; ibmgoo; 2012.09.15 2012.07.05
list (43;"44";45); ("abc";0101b;);(("abc";1 2 3); ibmabc)
dictionary abc!42 43 44; nameage!(johncarolted;42 43)
table ([]name:johncarolted; age:42 43 44)
keyed table ([name:johncarolted] age:42 43 44)

Lists are zero or more items, separated by semicolons, and enclosed in parentheses. An item can be any noun.

A vector is a list in which all items are of the same datatype. It can be represented without parentheses. Numeric, boolean, char and symbol vectors have their own forms.

type example
numeric 42 43 44
date 2012.09.15 2012.07.05
char "abc"
boolean 0101b
symbol ibmattora

The syntactic class of nouns includes all data structures. Operators, functions and adverbs can be given noun syntax by listing or parenthesising them.

q)count(+)
1
q)count(+;within;\)
3


### Attributes¶

Attributes are metadata that apply to lists of special form. They are often used on a dictionary domain or a table column to reduce storage requirements or speed retrieval.

s#2 2 3 sorted 0
u#2 4 5 unique 16*u
p#2 2 1 parted (4*u;16*u;4*u+1)
g#2 1 2 grouped (4*u;16*u;4*u+1;4*n)

The byte overheads use n (number of elements) and u (number of uniques).

• u is for unique lists.
• p and g are for lists with a lot of repetition.

s#, u# and g# are preserved on append in memory, if possible. Only s# is preserved on append to disk.

To set or unset an attribute:

q)s#1 2 3
s#1 2 3
q)#s#1 2 3
1 2 3

Setting or unsetting an attribute other than s, i.e. upg, causes a copy of the object to be made. Setting/unsetting the s attribute on a list which is already sorted will not cause a copy to be made, and hence will affect the original list in-place. Setting the s attr on a dictionary or table, where the key is already in sorted order, in order to obtain a step-function, causes the s attribute to be set in place for the key but copies the outer object.
q)t:([1 2 4]y:7 8 9);s#t;attr each (t;key t)
s


## Names and namespaces¶

Names consist of upper- and lower-case alphabetics. They may contain, but not begin with, underscores and numbers. For example: a, foo, foo2_bar.

A namespace is a container or context within which a name resolves to a unique value. Namespaces are children of the root namespace (usually just root) and are designated by a dot prefix. Names in the root have no prefix. The root namespace of a q session is parent to multiple namespaces, e.g. h, Q and z. (Namespaces with 1-character names – of either case – are reserved for use by Kx.)

q).z.p                         / UTC timestamp
2017.02.01D14:58:38.579614000


## Functions¶

Functions are:

1. operators and primitive functions, eg +, count
2. as defined in the lambda notation, eg {x+2*y}
3. as derived from (1) and (2) by adverbs, eg +/, count'
4. q-SQL functions, e.g. select

Functions are first-class objects and can be passed as arguments to other functions. Functions that take other functions as arguments are known as higher-order functions.

### Reserved words¶

The following reserved words denote functions that are not also operators.

.Q.res (reserved words)

## Operators¶

Operators are primitive binary functions that may be applied infix.

q)|[2;3]                 / maximum, prefix form
3
q)2|3                    / maximum, infix form
3
q)rotate[2;0 1 2 3 4 5]  / prefix form
2 3 4 5 0 1
q)2 rotate 0 1 2 3 4 5   / infix form
2 3 4 5 0 1

Operators are denoted by glyphs or reserved words or both – see note below on minimum and maximum. (They cannot be defined using the lambda notation.)

### Glyphs¶

Minimum and maximum

The minimum operator is denoted by both the & glyph and the reserved word and. The maximum operator is denoted by both the | glyph and the reserved word or.

### Reserved words¶

The following reserved words denote operators.

.Q.res (reserved words)

Adverbs are primitive higher-order functions: they return derivatives (derived functions). They are denoted by six overloaded glyphs: ', /, \, ':, /: and \:.

q)+/[2 3 4]  / reduce 2 3 4 with +
9
q)*/[2 3 4]  / reduce 2 3 4 with *
24


## Control words¶

The control words do, if and while govern evaluation.

## Views¶

A view is a calculation that is re-evaluated only if the values of the underlying dependencies have changed since its last evaluation. Views can help avoid expensive calculations by delaying propagation of change until a result is demanded.

The syntax for the definition is

q)viewname::[expression;expression;…]expression

The act of defining a view does not trigger its evaluation.

A view should not have side-effects, i.e. should not update global variables.

## System commands¶

Expressions beginning with \ are system commands or multiline comments (see above).

q)/ load the script in file my_app.q
q)\l my_app.q


## Scripts¶

A script is a text file; its lines a list of expressions and/or system commands, to be executed in sequence. By convention, script files have the extension q.

Within a script

• function definitions may extend over multiple lines
• an empty comment begins a multiline comment.