Operator reference

The complete operator vocabulary of @johnhenry/jth-stdlib (~110 operators), as registered by the compiler’s default preamble. Three reading notes first:

• Arguments pop in push order. 10 3 - is 10 - 3. Examples below show the stack as you’d write it.
• Variadic operators consume the entire stack — they are flagged in their descriptions. Don’t leave stray values behind when you use one.
• Names with a / are aliases: both spellings resolve to the same operator.

Arithmetic

Operator	Description	Example
+ / plus	Addition	2 3 + => 5
- / minus	Subtraction	10 3 - => 7
* / mul	Multiplication	4 5 * => 20
/ / div	Division	15 4 / => 3.75
% / mod	Modulo	17 5 % => 2
%%	Remainder	-17 5 %% => -2
** / pow	Exponentiation	2 8 ** => 256
++	Increment	5 ++ => 6
--	Decrement	5 -- => 4
abs	Absolute value	-5 abs => 5
sqrt / √	Square root	16 sqrt => 4
floor	Floor	3.7 floor => 3
ceil	Ceiling	3.2 ceil => 4
round	Round	3.5 round => 4
trunc	Truncate	3.9 trunc => 3
log	Natural logarithm	1 log => 0
⋅	Multiply (unicode)	4 5 ⋅ => 20
÷	Divide (unicode)	15 3 ÷ => 5

Variadic math

All of these consume the whole stack.

Operator	Description	Example
Σ	Sum of all stack values	1 2 3 Σ => 6
Π	Product of all stack values	2 3 4 Π => 24
min	Minimum of all stack values	3 7 1 min => 1
max	Maximum of all stack values	3 7 1 max => 7

Stack manipulation

Operator	Description	Example
noop / ∅	Do nothing	5 noop => stack unchanged
clear	Clear the stack	1 2 3 clear => []
...	Spread (array to stack)	[1 2 3] ... => 1 2 3 on stack
drop	Remove top	1 2 drop => [1]
dupe / dup	Duplicate top	5 dupe => [5, 5]
copy	Duplicate entire stack	1 2 copy => [1, 2, 1, 2]
swap	Swap top two	1 2 swap => [2, 1]
over	Copy second to top	1 2 over => [1, 2, 1]
rot	Rotate third to top	1 2 3 rot => [2, 3, 1]
reverse	Reverse stack	1 2 3 reverse => [3, 2, 1]
count / depth	Push stack depth	1 2 count => [1, 2, 2]
collect	All items to array (variadic)	1 2 3 collect => [[1, 2, 3]]
peek	Log top (without removing)	42 peek => logs 42
peek-all	Log entire stack	1 2 peek-all => logs 1 2

Comparison

Operator	Description	Example
= / eq?	Strict equal	3 3 = => true
==	Loose equal	3 "3" == => true
!= / ne?	Not equal	3 4 != => true
< / lt?	Less than	2 5 < => true
<= / le?	Less than or equal	3 3 <= => true
> / gt?	Greater than	5 2 > => true
>= / ge?	Greater than or equal	3 3 >= => true
<=>	Spaceship (three-way)	3 5 <=> => 1

Note the reversal from JavaScript: single = is strict equality; == is loose.

Logic

Operator	Description	Example
&&	Logical AND	true false && => false
||	Logical OR	true false || => true
xor	Exclusive OR	true false xor => true
nand	NOT AND	true true nand => false
nor	NOT OR	false false nor => true
~~ / not	Logical NOT	true ~~ => false

Control flow

Operator	Description	Example
if	Conditional branch (3-arg)	#[ "no" ] #[ "yes" ] true if => "yes"
if	Start conditional chain (2-arg)	#[ "yes" ] true if
elseif	Chain conditional	#[ "alt" ] cond elseif
else	Default branch	#[ "default" ] else
when	Keep if truthy	42 true when => 42
drop-when	Drop if truthy	42 true drop-when => []
keep-if	Keep value if truthy	42 true keep-if => 42
drop-if	Drop value if truthy	42 true drop-if => []
times	Repeat block N times	#[ "hi" peek ] 3 times
while	Loop while condition truthy	#[ cond ] #[ body ] while
until	Loop until condition truthy	#[ cond ] #[ body ] until
break	Exit current loop	break

In the 3-argument if, remember the source order: false-block, true-block, condition. See the tutorial.

Error handling

Operator	Description	Example
try	Catch errors from block	#[ "fail" throw ] try => Error on stack
throw	Throw an error	"oops" throw
error?	Check if top is Error	err error? => true

Strings

Operator	Description	Example
len	Length	"hello" len => 5
upper	Uppercase	"hi" upper => "HI"
lower	Lowercase	"HI" lower => "hi"
trim	Trim whitespace	" hi " trim => "hi"
strcat	Concatenate	"ab" "cd" strcat => "abcd"
strseq	Reverse concat	"ab" "cd" strseq => "cdab"
startsWith / starts?	Starts with prefix?	"hello" "hel" starts? => true
endsWith / ends?	Ends with suffix?	"hello" "llo" ends? => true
indexOf / index-of	Index of substring	"hello" "ell" indexOf => 1

Type checking

Operator	Description	Example
typeof	Push type string	42 typeof => "number"
number?	Is number?	42 number? => true
string?	Is string?	"hi" string? => true
array?	Is array?	[1] array? => true
nil?	Is null/undefined?	null nil? => true
function?	Is function?	#[ ] function? => true
empty?	Is empty?	"" empty? => true
contains?	Contains element?	[1 2 3] 2 contains? => true

Arrays

Operator	Description	Example
push	Append to array	[1 2] 3 push => [1,2,3]
pop	Remove last (pushes array, then item)	[1 2 3] pop => [1,2] and 3
shift	Remove first (pushes array, then item)	[1 2 3] shift => [2,3] and 1
unshift	Prepend to array	[2 3] 1 unshift => [1,2,3]
suppose	Add to collection	[1 2] 3 suppose => [1,2,3]
flatten	Flatten all stack values (variadic)	[1] [2 3] flatten => 1 2 3 on stack
map	Apply block to each element	[1 2 3] #[ 2 * ] map => [2,4,6]
filter	Keep elements where block is truthy	[1 2 3 4] #[ 2 % 0 = ] filter => [2,4]
reduce	Accumulate with block and init	[1 2 3] 0 #[ + ] reduce => 6
fold	Alias for reduce (catamorphism)	[1 2 3] 0 #[ + ] fold => 6
bend	Unfold/anamorphism from seed	1 #[ 5 <= ] #[ dupe 1 + ] bend => [1,2,3,4,5]

Objects / dictionaries

Operator	Description	Example
keys	Get keys	{ "a" 1 } keys => ["a"]
values	Get values	{ "a" 1 } values => [1]
entries	Get entries	{ "a" 1 } entries => [["a",1]]
merge	Merge objects	obj1 obj2 merge
record	Build object from stack pairs (variadic)	1 "a" record => {a: 1}

Serialization

Operator	Description	Example
into-json	Stringify to JSON	{ "a" 1 } into-json => '{"a":1}'
from-json	Parse JSON string	'{"a":1}' from-json => {a: 1}
to-json	Parse JSON (legacy alias for from-json)	'{"a":1}' to-json => {a: 1}
into-lines	Join by newline	["a" "b"] into-lines => "a\nb"
from-lines	Split by newline	"a\nb" from-lines => ["a","b"]
to-lines	Split by newline (legacy alias for from-lines)	"a\nb" to-lines => ["a","b"]

Watch the legacy aliases: to-json parses (it does not stringify). Prefer the unambiguous into-/from- pairs in new code.

Async

Operator	Description	Example
_	Await a promise	promise _
__	Promise.all (variadic, consumes stack)	p1 p2 __

Meta / execution

Operator	Description	Example
apply / exec	Execute block	#[ 2 3 + ] apply => 5
$	Execute block (legacy)	#[ 2 3 + ] $ => 5
$$	Execute and spread	#[ 2 3 + ] $$
<<-	Rewind all	Moves pointer to start
->>	Skip all	Moves pointer to end

Combinators

Operator	Description	Example
each	Apply block to each stack item	1 2 3 #[ 2 * ] each
fanout	Run value through multiple blocks	5 #[ 2 * ] #[ 1 + ] fanout => 10, 6
zip	Pair elements from two arrays	[1 2] ["a" "b"] zip => [[1,"a"],[2,"b"]]
compose	Combine blocks into pipeline	#[ 2 * ] #[ 1 + ] compose

Iterators

Operator	Description	Example
iter	Create iterator	[1 2 3] iter
next	Get next value	iterator next
..	Exhaust to array	iterator ..

Sequences

Operator	Description	Example
fibonacci	Fibonacci step: pops (a, b), pushes (b, a, a+b)	0 1 fibonacci => 1 0 1

Statistics

All statistics operators are variadic — they consume the entire stack.

Operator	Description	Example
mean / x̄	Arithmetic mean	1 2 3 mean => 2
median	Median value	1 2 3 median => 2
mode	Most frequent	1 1 2 mode => 1
modes	All modes	1 1 2 2 modes => [1, 2]

Hyperoperations

Operator	Description	Example
***	Tetration	2 3 ***
****	Pentation	2 3 ****

Dynamic operator patterns

Prefix any number to an arithmetic operator to make a one-argument version. Semantics: N op x — the prefix number is the left operand:

Pattern	Description	Example
N+	N + x	10 3+ => 13
N-	N - x	20 3- => -17 (3 - 20)
N*	N * x	7 2* => 14
N/	N / x	50 100/ => 2 (100 / 50)
N%	N % x	17 5% => 5
N**	N ** x	3 2** => 8 (2 ** 3)
Nlog	Log base N of x	100 10log => 2

Dynamic patterns are resolved through the runtime registry’s pattern mechanism, which is also why jth-eval’s restricted sandbox denies them: an open-ended name family can’t be enumerated into an allowlist.