Quotations

Quotations are the general term for anonymous functions or lambdas. They denote a snippet of code which can be executed later. Their exact syntax varies by language. For example, Factor denotes quotations using square-brackets. Whereas, Tal and Postscript denote them using curly-brackets. Regardless of syntax, they are core to constructing higher-order functions in concatenative languages.

Higher-Order Function

A higher-order function is an operation that utilize other functions as inputs or create new functions as outputs. This feature is leverage by a core utility of concatenative programming: combinators. They enable a programmer to name code not values.

Example of Quotations

Factor

! { 1 4 9 16 }
{ 1 2 3 4 } [ sq ] map 

Kitten

// [10, 20, 30]
[1, 2, 3] { (* 10) } map

Tal

( 02 04 06 08 0a )
{ 01 02 03 04 } { DUP ADD JMP2r } map]

Implementation of %map%:
[tal{@map ( | arr* f* -- arr* )
	SWP2r LITr _&f STR2r
	SWP2r STH2r
	DUP2k #0002 SUB2 LDA2 ADD2 SWP2
	&>l ( -- )
		STH2k LDAk [ LIT2 &f $2 ] JSR2 STH2r STA
		INC2 GTH2k ?&>l
	POP2 POP2 JMP2r