seqlua
view README @ 31:4fc9090ada1d
Mention 3 extra elements on stack in README; Changed order of two instructions in seqlualib.c
| author | jbe |
|---|---|
| date | Sat Aug 23 23:35:10 2014 +0200 (2014-08-23) |
| parents | 367fc70acc15 |
| children | 3ff7cec8d3ce |
line source
1 seqlua: Extended sequences and iterators in Lua
2 ===============================================
4 This is an experimental package to extend Lua in the following manner:
6 * allow ``ipairs(seq)`` to accept tables as well as functions (i.e function
7 iterators),
8 * add a new function ``string.concat(separator, seq)`` to concat either table
9 entries or function return values,
10 * provide auxiliary C functions and macros to simplify iterating over both
11 tables and iterator functions with the same statement.
13 In all cases, existing ``__index``, ``__len``, or ``__ipairs`` metamethods are
14 respected. The ``__ipairs`` metamethod takes precedence.
17 Lua part of the library
18 -----------------------
20 The modified ``ipairs(seq)`` and the new ``string.concat(sep, seq)`` functions
21 accept either a table or a function as ``seq``. This is demonstrated in the
22 following examples:
24 require "seqlua"
26 t = {"a", "b", "c"}
28 for i, v in ipairs(t) do
29 print(i, v)
30 end
31 -- prints:
32 -- 1 a
33 -- 2 b
34 -- 3 c
36 print(string.concat(",", t))
37 -- prints: a,b,c
39 function alphabet()
40 local letter = nil
41 return function()
42 if letter == nil then
43 letter = "a"
44 elseif letter == "z" then
45 return nil
46 else
47 letter = string.char(string.byte(letter) + 1)
48 end
49 return letter
50 end
51 end
53 for i, v in ipairs(alphabet()) do
54 print(i, v)
55 end
56 -- prints:
57 -- 1 a
58 -- 2 b
59 -- 3 c
60 -- ...
61 -- 25 y
62 -- 26 z
64 print(string.concat(",", alphabet()))
65 -- prints: a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z
67 function filter(f)
68 return function(seq)
69 return coroutine.wrap(function()
70 for i, v in ipairs(seq) do f(v) end
71 end)
72 end
73 end
75 alpha_beta_x = filter(function(v)
76 if v == "a" then
77 coroutine.yield("alpha")
78 elseif v == "b" then
79 coroutine.yield("beta")
80 elseif type(v) == "number" then
81 for i = 1, v do
82 coroutine.yield("X")
83 end
84 end
85 end)
87 print((","):concat(alpha_beta_x{"a", 3, "b", "c", "d"}))
88 -- prints: alpha,X,X,X,beta
90 print((","):concat(alpha_beta_x(alphabet())))
91 -- prints: alpha,beta
94 C part of the library
95 ---------------------
97 In ``seqlualib.h``, the following macro is defined:
99 #define seqlua_iterloop(L, iter, idx) \
100 for ( \
101 seqlua_iterinit((L), (iter), (idx)); \
102 seqlua_iternext(iter); \
103 )
105 and
107 #define seqlua_iterloopauto(L, iter, idx) \
108 for ( \
109 seqlua_iterinit((L), (iter), (idx)); \
110 seqlua_iternext(iter); \
111 lua_pop((L), 1) \
112 )
114 This macro allows iteration over either tables or iterator functions as the
115 following example function demonstrates:
117 int printcsv(lua_State *L) {
118 seqlua_Iterator iter;
119 seqlua_iterloop(L, &iter, 1) {
120 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
121 fputs(luaL_tolstring(L, -1, NULL), stdout);
122 // two values need to be popped (the value pushed by
123 // seqlua_iternext and the value pushed by luaL_tolstring)
124 lua_pop(L, 2);
125 }
126 fputs("\n", stdout);
127 return 0;
128 }
130 printcsv{"a", "b", "c"}
131 -- prints: a,b,c
133 printcsv(assert(io.open("testfile")):lines())
134 -- prints: line1,line2,... of "testfile"
136 NOTE: During iteration using ``seqlua_iterloop``, ``seqlua_iterloopauto``, or
137 ``seqlua_iterinit``, three extra elements are stored on the stack (additionally
138 to the value). These extra elements are removed automatically when the loop ends
139 (i.e. when ``seqlua_iternext`` returns zero). The value pushed onto the stack
140 for every iteration step has to be removed manually from the stack, unless
141 ``seqlua_iterloopauto`` is used.