Built-in Functions

Arithmetic Operators

Operator	Description	Example	Result
+	Add	+3 4	7
-	Subtract	-10 3	7
*	Multiply	*3 4	12
/	Divide	/10 2	5
%	Modulo	%10 3	1

Comparison Operators

Operator	Description	Example	Result
==	Equal	==a b	true/false
!=	Not equal	!=a b	true/false
>	Greater than	>a b	true/false
<	Less than	<a b	true/false
>=	Greater or equal	>=a b	true/false
<=	Less or equal	<=a b	true/false

Logic

Operator	Description	Example
&	Logical AND	&a b
|	Logical OR	|a b
!	Logical NOT	!a

Text

Function	Signature	Description	Example
cat	t t > t	Concatenate two strings	cat "hello" " world" → "hello world"
len	t > n	String length	len "hello" → 5
trm	t > t	Trim whitespace	trm " hi " → "hi"
spl	t t > L t	Split string by delimiter	spl "a,b,c" "," → ["a","b","c"]
has	t t > b	Check if string contains substring	has "hello" "ell" → true
rgx	t t > L t	Regex match (returns captures)	rgx "abc123" "[0-9]+" → ["123"]
fmt	t ... > t	Format string with values	fmt "{} is {}" "sky" "blue"

Collections (Lists)

Function	Alias	Signature	Description	Example
len	length	L _ > n	List length	len [1,2,3] → 3
hd	head	L _ > _	First element	hd [1,2,3] → 1
tl	tail	L _ > L _	All elements except first	tl [1,2,3] → [2,3]
rev	reverse	L _ > L _	Reverse a list	rev [1,2,3] → [3,2,1]
srt	sort	L _ > L _	Sort a list	srt [3,1,2] → [1,2,3]
srt	sort	fn L _ > L _	Sort by key function	srt cmp xs
slc	slice	L _ n n > L _	Slice (start, end)	slc [1,2,3,4] 1 3 → [2,3]
flat	flatten	L L _ > L _	Flatten nested lists	flat [[1,2],[3]] → [1,2,3]
unq	unique	L _ > L _	Remove duplicates	unq [1,2,2,3] → [1,2,3]
has	contains	L _ _ > b	Check if list contains element	has [1,2,3] 2 → true

Higher-Order Functions

Function	Alias	Signature	Description	Example
map		fn L _ > L _	Apply function to each element	map dbl [1,2,3]
flt	filter	fn L _ > L _	Keep elements where function returns true	flt pos [1,-2,3]
fld	fold	fn _ L _ > _	Reduce list to single value	fld add 0 [1,2,3]
grp	group	fn L _ > M t L _	Group elements by function result	grp cat xs

Aggregation

Function	Signature	Description	Example
sum	L n > n	Sum a list of numbers	sum [1,2,3] → 6
avg	L n > n	Average of a list of numbers	avg [2,4,6] → 4

Maps

Function	Signature	Description	Example
mmap	> M	Create empty map	m=mmap
mget	M t > _	Get value by key	mget m "key"
mset	M t _ > M	Set key-value pair	mset m "key" val
mhas	M t > b	Check if key exists	mhas m "key"
mkeys	M > L t	Get all keys	mkeys m
mvals	M > L _	Get all values	mvals m
mdel	M t > M	Remove key, return new map	mdel m "key"

Type Conversion

Function	Signature	Description	Example
str	_ > t	Convert to string	str 42 → "42"
num	t > n	Parse string to number	num "42" → 42
abs	n > n	Absolute value	abs -5 → 5
flr	n > n	Floor	flr 3.7 → 3
cel	n > n	Ceiling	cel 3.2 → 4
rnd	n n > n	Round to N decimal places	rnd 3.14159 2 → 3.14

I/O & HTTP

Function	Signature	Description	Example
get	t > R t t	HTTP GET (returns Result)	get "https://..."
$	t > R t t	HTTP GET shorthand (sugar for get)	$"https://..."
post	t t > R t t	HTTP POST (url, body)	post url body
get	t M > R t t	HTTP GET with headers	get url headers
post	t t M > R t t	HTTP POST with headers	post url body headers
rd	t > R t t	Read file	rd "data.txt"
rd	t t > R t t	Read file with format	rd "data.csv" "csv"
wr	t t > R t t	Write file (path, content)	wr "out.txt" data
wr	t t t > R t t	Write file with format	wr "out.json" data "json"
env	t > R t t	Read environment variable	env "API_KEY"

Note: $ is syntactic sugar -$url compiles to get url. HTTP builtins (get, $, post) require the native binary; they are not available in the npm/WASM build.

JSON

Function	Signature	Description	Example
rdb	t t > R _ t	Parse data (format: "json", "csv")	rdb data "json"
jpth	t t > R t t	Extract JSON path	jpth data "users.0.name"
jdmp	_ > t	Dump value as JSON string	jdmp [1,2,3]
jpar	t > R _ t	Parse JSON string to value	jpar '{"a":1}'

Output

Function	Signature	Description	Example
prnt	_ > _	Print value and return it	prnt "hello"

Time

Function	Signature	Description	Example
now	> n	Current Unix timestamp (seconds)	now

Auto-unwrap !

Any function returning R (Result) can be called with ! to auto-unwrap:

ilo

r=$url           -- r is R t t (Result)
v=$!url           -- v is t (auto-unwrapped, propagates error)
data=rdb! r "json"  -- auto-unwrap parse result

See Error Handling for full details on !, ?, ??, and Result types.

Dot-notation indexing

Access list elements and record fields with .:

ilo

xs.0          -- first element of list xs
xs.2          -- third element
user.name     -- field "name" of record/map
data.users.0  -- chained access

Safe navigation with .? returns nil instead of erroring on missing keys:

ilo

user.?email   -- nil if "email" doesn't exist

Builtin aliases

All builtins accept long-form names that resolve to the canonical short form. ilo will emit a hint suggesting the short form:

Long form	Short form
length	len
head	hd
tail	tl
reverse	rev
sort	srt
slice	slc
unique	unq
filter	flt
fold	fld
flatten	flat
concat	cat
contains	has
group	grp
average	avg
print	prnt
trim	trm
split	spl
format	fmt
regex	rgx
read	rd
write	wr
readbuf	rdb
floor	flr
ceil	cel
round	rnd
string	str
number	num