1 ----------------------------------------------------------------------
2 -- Metalua samples: $Id$
4 -- Summary: Lists by comprehension
6 ----------------------------------------------------------------------
8 -- Copyright (c) 2006-2007, Fabien Fleutot <metalua@gmail.com>.
10 -- This software is released under the MIT Licence, see licence.txt
13 --------------------------------------------------------------------------------
15 -- This extension implements list comprehensions, similar to Haskell and
16 -- Python syntax, to easily describe lists.
18 --------------------------------------------------------------------------------
20 -{ extension "match" }
22 local function dots_builder (x) return `Dots{ x } end
24 local function for_builder (x, h)
26 | `Comp{ _, acc } -> table.insert (acc, h[1]); return x
27 | `Pair{ _, _ } -> error "No explicit key in a for list generator"
28 | _ -> return `Comp{ x, {h[1]} }
32 local function if_builder (x, p)
34 | `Comp{ _, acc } -> table.insert (acc, `If{ p[1] }); return x
35 | `Pair{ _, _ } -> error "No explicit key in a list guard"
36 | _ -> return `Comp{ x, p[1] }
40 local function comp_builder(core, list, no_unpack)
41 -- [ti] = temp var holding table.insert
42 -- [v] = variable holding the table being built
43 -- [r] = the core of the list being built
44 local ti, v, r = mlp.gensym "table_insert", mlp.gensym "table"
46 -----------------------------------------------------------------------------
47 -- 1 - Build the loop's core: if it has suffix "...", every elements of the
48 -- multi-return must be inserted, hence the extra [for] loop.
49 -----------------------------------------------------------------------------
52 local w = mlp.gensym()
53 r = +{stat: for -{w} in values( -{x} ) do -{ `Call{ ti, v, w } } end }
55 r = `Set{ { `Index{ v, k } }, { w } }
56 | _ -> r = `Call{ ti, v, core }
59 -----------------------------------------------------------------------------
60 -- 2 - Stack the if and for control structures, from outside to inside.
61 -- This is done in a destructive way for the elements of [list].
62 -----------------------------------------------------------------------------
63 for i = #list, 1, -1 do
64 table.insert (list[i], {r})
68 return `Stat{ { `Local{ {ti, v}, { +{table.insert}, `Table} }, r }, v }
71 local -{ti}, -{v} = table.insert, { }
72 -{r}; return unpack(-{v})
77 local function table_content_builder (list)
79 | { `Comp{ y, acc } } -> return comp_builder( y, acc, "no unpack")
81 local tables = { `Table }
82 local ctable = tables[1]
83 local function flush() ctable=`Table; table.insert(tables, ctable) end
84 for x in values(list) do
86 | `Comp{ y, acc } -> table.insert(ctable, comp_builder(y, acc)); flush()
87 | `Dots{ y } -> table.insert(ctable, y); flush()
88 | _ -> table.insert (ctable, x);
92 | { x } | { x, { } } -> return x
94 if #tables[#tables]==0 then table.remove(tables) end --suppress empty table
95 return `Call{ +{table.cat}, unpack(tables) }
100 mlp.table_field = gg.expr{ name="table cell",
101 primary = mlp.table_field,
102 suffix = { name="table cell suffix",
103 { "...", builder = dots_builder },
104 { "for", mlp.for_header, builder = for_builder },
105 { "if", mlp.expr, builder = if_builder } } }
107 mlp.table_content.builder = table_content_builder
110 mlp.stat:add{ "for", gg.expr {
111 primary = for_header,
113 { "for", mlp.for_header, builder = for_builder },
114 { "if", mlp.expr, builder = if_builder } } },
115 "do", mlp.block, "end", builder = for_stat_builder }
118 --------------------------------------------------------------------------------
119 -- Back-end for improved index operator.
120 --------------------------------------------------------------------------------
121 local function index_builder(a, suffix)
123 -- Single index, no range: keep the native semantics
124 | { { e, false } } -> return `Index{ a, e }
125 -- Either a range, or multiple indexes, or both
127 local r = `Call{ +{table.isub}, a }
128 local function acc (x,y) table.insert (r,x); table.insert (r,y) end
129 for seq in ivalues (ranges) do
131 | { e, false } -> acc(e,e)
132 | { e, f } -> acc(e,f)
139 --------------------------------------------------------------------------------
140 -- Improved "[...]" index operator:
141 -- * support for multi-indexes ("foo[bar, gnat]")
142 -- * support for ranges ("foo[bar ... gnat]")
143 --------------------------------------------------------------------------------
144 mlp.expr.suffix:del '['
145 mlp.expr.suffix:add{ name="table index/range",
147 gg.sequence { mlp.expr, gg.onkeyword{ "...", mlp.expr } } ,
148 separators = { ",", ";" } },
149 "]", builder = index_builder }