Lists

4.6.1 Lists

TBoS p.63-73, SD

Lists in Shen are produced by placing the items in square brackets. The list of the numbers 1, 2 and 3 is just [1 2 3]. 'head' and 'tail' take the head and tail of a list.

(0-) [1 (+ 1 1) (+ 1 2)]
[1 2 3]

(1-) (head [1 2 3])
1

(2-) (tail [1 2 3])
[2 3]

'cons' adds an element to the front of a list. Shen includes an infix | which works in the manner of Prolog; '[1 2 | [3]]' conses 1 and 2 to the list [3]. If the second argument to 'cons' is not a list then the result is a dotted pair in Lisp jargon.

(0-) (cons 1 [2 3])
[1 2 3]

(1-) [1 2 | [3]]
[1 2 3]

(2-) [1 | (+ 1 1)]
[1 | 2]

4. The Core Language

4.6 Sequences

5 Defining Functions

6. Packages

7. Shen-YACC

8. Shen Prolog

9. Types

10 Sequent Calculus

10.2 Exotic Types