Overloaded operators

Many non-alphabetic keyboard characters are overloaded. Operator overloads are resolved by rank, and sometimes by the type of argument/s.

@ at

rank	syntax	semantics
2	l@i, @[l;i]	Index At
2	f@y, @[f;y]	Apply At
3	@[f;y;e]	Trap At
3	@[d;i;u]	Amend At
4	@[d;i;m;my]	Amend At
4	@[d;i;:;y]	Replace At

\ backslash

rank	syntax	semantics
n/a	\	ends multiline comment
n/a	\	abort
1	(u\), u\[d]	Converge
2	n u\d, u\[n;d]	Do
2	t u\d, u\[t;d]	While
2	x v\y, v\[x;y;z;…]	map-reduce

d: data                   n: non-negative integer atom
u: unary value            t: test value
v: value rank>1           x: atom or vector
                          y, z…: conformable atoms or lists

! bang

rank	syntax	semantics
2	x!y	Dict: make a dictionary
2	i!ts	Enkey: make a simple table keyed
2	0!tk	Unkey: make a keyed table simple
2	noasv!iv	Enumeration from index
2	sv!h	Flip Splayed or Partitioned
2	0N!y	display y and return it
2	-i!y	internal function
4	![t;c;b;a]	Update, Delete

a: select specifications
b: group-by specifications
c: where-specifications
h: handle to a splayed or partitioned table
i: integer >0
noasv: symbol atom, the name of a symbol vector
sv: symbol vector
t: table
tk: keyed table
ts: simple table
x,y: same-length lists

- dash

Syntax: immediately left of a number, indicates its negative.

q)neg[3]~-3
1b

Otherwise

rank	example	semantics
2	2-3	Subtract

. dot

rank	syntax	semantics
2	l . i, .[l;i]	Index
2	g . gx, .[g;gx]	Apply
3	.[g;gx;e]	Trap
3	.[d;i;u]	Amend
4	.[d;i;m;my]	Amend
4	.[d;i;:;y]	Replace

$ dollar

rank	example	semantics
3	$[x>10;y;z]	Cond: conditional evaluation
2	"h"$y, `short$y, 11h$y	Cast: cast datatype
2	"H"$y, -11h$y	Tok: interpret string as data
2	x$y	Enumerate: enumerate y from x
2	10$"abc"	Pad: pad string
2	(1 2 3f;4 5 6f)$(7 8f;9 10f;11 12f)	dot product, matrix multiply, mmu

# hash

rank	example	semantics
2	2 3#til 6	Take
2	s#1 2 3	Set Attribute

? query

rank	example	semantics
2	"abcdef"?"cab"	Find y in x
2	10?1000, 5?01b	Roll
2	-10?1000, -1?`yes`no	Deal
2	0N?1000, 0N?`yes`no	Permute
2	x?v	extend an enumeration: Enum Extend
3	?[11011b;"black";"flock"]	Vector Conditional
3	?[t;i;p]	Simple Exec
4	?[t;c;b;a]	Select, Exec
5	?[t;c;b;a;n]	Select
6	?[t;c;b;a;n;(g;cn)]	Select

' quote

rank	syntax	semantics
1	(u')x, u'[x], x b'y, v'[x;y;…]	Each: iterate u, b or v itemwise
1	'msg	Signal an error
1	int'[x;y;…]	Case: successive items from lists
2	'[u;v]	Compose u with v

u:  unary value         int:  int vector
b:  binary value        msg:  symbol or string
v: value of rank ≥1     x, y: data

': quote-colon

rank	example	semantics
1	u':	Each Parallel with unary u
1	b':	Each Prior with binary b

/ slash

rank	syntax	semantics
n/a	/a comment	comment: ignore rest of line
1	(u/)y, u/[y]	Converge
1	n u/ y, u/[n;y]	Do
1	t u/ y, u/[t;y]	While
1	(v/)y, v/[y]	map-reduce: reduce a list or lists

u: unary value              t: test value
v: value rank ≥1            y: list
n: non-negative int atom

Syntax: a space followed by / begins a trailing comment. Everything to the right of / is ignored.

q)2+2 / we know this one
4

A / at the beginning of a line marks a comment line. The entire line is ignored.

q)/nothing in this line is evaluated

In a script, a line with a solitary / marks the beginning of a multiline comment. A multiline comment is terminated by a \ or the end of the script.

/
A script to add two numbers.
Version 2018.1.19
\
2+2
/
That's all folks.

_ underscore

rank	example	semantics
2	3_ til 10	Cut, Drop

Names can contain underscores

Best practice is to use a space to separate names and the Cut and Drop operators.

Unary forms

Many of the operators tabulated above have unary forms in k.

Exposed infrastructure