3 ----------------------------------------------------------------------
4 -- * [loop_tags] are the tags of statements which support continue.
5 -- * [loop_keywords] are the initial keywords which trigger the parsing
6 -- of these statements: they're indeed indexed by keyword in [mlp.stat].
7 ----------------------------------------------------------------------
9 local loop_tags = table.transpose{ "Forin", "Fornum", "While", "Repeat" }
10 local loop_keywords = { "for", "while", "repeat" }
12 ----------------------------------------------------------------------
13 -- This function takes the AST of a continue-enabled loop, parse
14 -- its body to find all instances of [`Continue]. If any of them
15 -- is found ([label~=nil]), they're transformed in [`Goto{...}], and
16 -- the corresponding label is added at the end of the loop's body.
18 -- Caveat: if a [continue] appears in the non-body part of a loop
19 -- (and therefore is relative to some enclosing loop), it isn't
20 -- handled, and therefore causes a compilation error. This could
21 -- only happen due in a [`Stat{ }], however, since [`Function{ }]
22 -- cuts the search for [`Continue].
23 ----------------------------------------------------------------------
24 local function loop_transformer (ast)
26 local cfg = { stat = { }; expr = { } }
28 function cfg.stat.down (x)
29 if loop_tags[x.tag] then return 'break'
30 elseif x.tag=='Continue' then
31 if not label then label = mlp.gensym 'continue' end
36 function cfg.expr.down (x)
37 return x.tag=='Function' and 'break'
40 local loop_body = ast.tag=="Repeat" and ast[1] or ast[#ast]
41 walk.block (cfg, loop_body)
42 if label then table.insert (loop_body, `Label{ label }) end
45 ----------------------------------------------------------------------
46 -- Register the transformer for each kind of loop:
47 ----------------------------------------------------------------------
48 for keyword in values (loop_keywords) do
49 mlp.stat:get(keyword).transformers:add (loop_transformer)
52 mlp.lexer:add "continue"
53 mlp.stat:add{ "continue", builder = ||`Continue }