KBAT

KBAT (Killed By A Train)

KBAT is an esolang that is based on APL's trains. This language only has trains and recursion.

Syntax

{...} is a dyadic train and [...] is a monadic train.
'f means f is recursive. $ is the recursion operator inside f.
f?g:h is the conditional operator. If f(args) is truthy, then g is called. Otherwise, h is called.
Any literals are monadic constant functions. To make dyadic constant functions, place a dot before the literal.

Data types

• Integer. Only natural numbers are supported. 0 is falsy and any other number is truthy.
• String. Sequence of characters. Empty string is falsy and any non-empty string is truthy.
• List. Sequence of values. Empty list is falsy and any non-empty list is truthy.
• Undefined. Just like in JavaScript. Always falsy.

Types are implicitly converted:

Implicit conversions

Data\Target	Int	Str	List
Int	/	chr(n)	range(n)
Str	len(s)	/	[ord(c) for c in s]
List	len(l)	"".join([str(i) for i in l])	/
Undef	0	""	[]

Seq is str or list.

Built-in operators

Dyadic operators

Polymorphic operators work by converting the left argument to the right argument's type.

• +: Addition / Concatenation.
• <: Always returns the left argument.
• >: Always returns the right argument.
• /: Nth element of a list/string. Left: Seq, Right: Int.
• -: Subtraction / Set difference.
• =: Equality. Returns 0 or 1.
• *: Multiplication / Repetition.
• %: Remainder.

Monadic operators

• ;: Identity.
• #: Length.
• l: Wrap in a list.
• s: Repr.
• h: Int -> Successor, Seq -> car.
• t: Int -> Predecessor, Seq -> cdr.
• p: ParseInt. Returns undefined otherwise.

Examples

Prime sieve, accepts an integer from stdin (as string as its left argument):

[p+1+()tt'[;?[hl+{<'{<?{{h%}?{hl<+{t$}}:{t$}}:.()}$}h]:()]]