PLisp/parser.pl at master · tylergreen/PLisp · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
% Lisp grammar using Definite Clause Grammars

read_sexp(S) --> spaces, sexp(S), spaces.

sexp(S) --> list(S).
sexp(S) --> atom(S).

list(Ns) --> lparen, spaces, nodes(Ns), spaces, rparen.

nodes([N|Ns]) --> sexp(N), spaces, nodes(Ns).
nodes([]) --> [].

lparen --> [40].
rparen --> [41].

spaces --> [32], !, spaces.
spaces --> [].

atom(A) --> number(A).
atom(A) --> symbol(A).

number(N) --> integer(N).

symbol(S) -->
	char(C),
	chars(Cs),
	{ atom_chars(S,[C|Cs]) }.

char(C) -->
	[C],
	{ code_type(C,ascii) },
	{ \+code_type(C, digit) },
	{ \+C=32 }. % whitespace is ascii

chars([C|Cs]) --> char(C), !, chars(Cs).
chars([]) --> [].

integer(I) -->
        digit(D0),
        digits(D),
        { number_chars(I, [D0|D]) }.

digits([D|T]) -->
        digit(D), !,
        digits(T).
digits([]) -->
        [].

digit(D) -->
        [D],
        { code_type(D, digit) }.