/metalualib/mlp_ext.lua

 1--------------------------------------------------------------------------------
 2--
 3-- Non-Lua syntax extensions
 4--
 5--------------------------------------------------------------------------------
 6
 7module ("mlp", package.seeall)
 8
 9--------------------------------------------------------------------------------
10-- Alebraic Datatypes
11--------------------------------------------------------------------------------
12local function adt (lx)
13   local tagval = id (lx) [1]
14   local tagkey = {tag="Pair", {tag="String", "tag"}, {tag="String", tagval} }
15   if lx:peek().tag == "String" or lx:peek().tag == "Number" then
16      return { tag="Table", tagkey, lx:next() }
17   elseif lx:is_keyword (lx:peek(), "{") then
18      local x = table (lx)
19      _G.table.insert (x, 1, tagkey)
20      return x
21   else return { tag="Table", tagkey } end
22end
23
24expr:add{ "`", adt, builder = fget(1) }
25
26--------------------------------------------------------------------------------
27-- Anonymous lambda
28--------------------------------------------------------------------------------
29local lambda_expr = gg.sequence{ 
30   "|", func_params_content, "|", expr,
31   builder= function (x) 
32      local li = x[2].lineinfo
33      return { tag="Function", x[1], 
34               { {tag="Return", x[2], lineinfo=li }, lineinfo=li } }
35   end }
36
37-- In an earlier version, lambda_expr took an expr_list rather than an expr
38-- after the 2nd bar. However, it happened to be much more of a burden than an
39-- help, So finally I disabled it. If you want to return several results, 
40-- use the long syntax.
41--------------------------------------------------------------------------------
42-- local lambda_expr = gg.sequence{ 
43--    "|", func_params_content, "|", expr_list,
44--    builder= function (x) 
45--       return {tag="Function", x[1], { {tag="Return", unpack(x[2]) } } } end }
46
47expr:add (lambda_expr)
48
49--------------------------------------------------------------------------------
50-- Allows to write "a `f` b" instead of "f(a, b)". Taken from Haskell.
51-- This is not part of Lua 5.1 syntax, so it's added to the expression
52-- afterwards, so that it's easier to disable.
53--------------------------------------------------------------------------------
54local function expr_in_backquotes (lx) return expr(lx, 35) end
55
56expr.infix:add{ name = "infix function", 
57   "`", expr_in_backquotes, "`", prec = 35, assoc="left", 
58   builder = function(a, op, b) return {tag="Call", op[1], a, b} end }
59
60
61--------------------------------------------------------------------------------
62-- table.override assignment
63--------------------------------------------------------------------------------
64
65mlp.lexer:add "<-"
66stat.assignments["<-"] = function (a, b)
67   assert( #a==1 and #b==1, "No multi-args for '<-'")                         
68   return { tag="Call", { tag="Index", { tag="Id", "table" },
69                                       { tag="String", "override" } },
70                        a[1], b[1]} 
71end
72
73--------------------------------------------------------------------------------
74-- C-style op+assignments
75--------------------------------------------------------------------------------
76local function op_assign(kw, op) 
77   local function rhs(a, b)
78      return { tag="Op", op, a, b } 
79   end
80   local function f(a,b) 
81      return { tag="Set", a, _G.table.imap(rhs, a, b) }
82   end
83   mlp.lexer:add (kw)
84   mlp.stat.assignments[kw] = f
85end
86
87_G.table.iforeach (op_assign, 
88                {"+=", "-=", "*=", "/="},
89                {"add", "sub", "mul", "div"})