# Assign¶

Name a value; amend a named value

## Simple assign¶

x:y

Where x is a name and y is a value, the value of y is associated with the name x.

q)a:42        / assign
q)a
42
q)a:3.14159   / amend

The Equal operator = tests equality. It has nothing to do with naming or amending values.

There is no need to declare the type of a variable.

A variable acquires the type of the value assigned to it. (Known as dynamic typing.)

q)type a:til 5    / integer vector
7h
q)type a:3.14159  / float atom
-9h

## Indexed assign¶

x[i]:y

Where

• x is the name of a list, dictionary or table
• i is a value that indexes x
• y is a scalar, or a list of the same length as i

the value of y is assigned to x at indexes i.

Indexed assignment cannot change the type of x.

If x is a vector (has negative type) then (=). abs type each(x;y) must be true.

Where x is a dictionary, assignment has upsert semantics.

q)d:tomdickharry!1 2 3
q)d[dickjane]:100 200
q)d
tom  | 1
dick | 100
harry| 3
jane | 200

## Assign through operator¶

x op:y     op:[x;y]
x[i]op:y   op:[x i;y]

Where

• op is a binary operator with infix syntax
• x is an applicable value (i.e. not an atom) in the left domain of op
• i is a value that indexes x
• y is a value in the right domain of op that conforms to either i or x
• x op y (or x[i]op y) has the same type as x

the value of x (or x[i]) becomes x op y (or x[i]op y).

q)s:("the";"quick";"brown";"fox")
q)s[1 2],:("er";"ish")
q)s
"the"
"quicker"
"brownish"
"fox"

Extend Assign-through-operator to derived functions, keywords and lambdas.

q)s:("the";"quick";"brown";"fox")
q)@[s;1 2;,;("er";"ish")]
"the"
"quicker"
"brownish"
"fox"

Amend At is more general, and extends assignment-through-operator to derived functions, keywords and lambdas.

If x is undefined, the identity element for op is used as a default.

q)bar
'bar
[0]  bar
^
q)bar+:1
q)bar
1

## Syntax¶

An expression with an assignment on the left returns no value to the console.

q)a:til 5
q)
The value of an assignment is the value assigned.
q)3+a:til 5
3 4 5 6 7
q)1+a[2]+:5
8
q)a
0 1 7 3 4`

Amend, Amend At
Q for Mortals §4.6.2 Simple q Amend