54 lines
2.1 KiB
Plaintext
Executable File
54 lines
2.1 KiB
Plaintext
Executable File
require "metalua.walk"
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----------------------------------------------------------------------
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-- * [loop_tags] are the tags of statements which support continue.
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-- * [loop_keywords] are the initial keywords which trigger the parsing
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-- of these statements: they're indeed indexed by keyword in [mlp.stat].
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----------------------------------------------------------------------
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local loop_tags = table.transpose{ "Forin", "Fornum", "While", "Repeat" }
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local loop_keywords = { "for", "while", "repeat" }
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----------------------------------------------------------------------
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-- This function takes the AST of a continue-enabled loop, parse
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-- its body to find all instances of [`Continue]. If any of them
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-- is found ([label~=nil]), they're transformed in [`Goto{...}], and
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-- the corresponding label is added at the end of the loop's body.
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--
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-- Caveat: if a [continue] appears in the non-body part of a loop
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-- (and therefore is relative to some enclosing loop), it isn't
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-- handled, and therefore causes a compilation error. This could
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-- only happen due in a [`Stat{ }], however, since [`Function{ }]
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-- cuts the search for [`Continue].
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----------------------------------------------------------------------
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local function loop_transformer (ast)
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local label
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local cfg = { stat = { }; expr = { } }
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function cfg.stat.down (x)
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if loop_tags[x.tag] then return 'break'
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elseif x.tag=='Continue' then
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if not label then label = mlp.gensym 'continue' end
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x <- `Goto{ label }
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end
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end
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function cfg.expr.down (x)
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return x.tag=='Function' and 'break'
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end
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local loop_body = ast.tag=="Repeat" and ast[1] or ast[#ast]
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walk.block (cfg, loop_body)
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if label then table.insert (loop_body, `Label{ label }) end
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end
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----------------------------------------------------------------------
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-- Register the transformer for each kind of loop:
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----------------------------------------------------------------------
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for keyword in values (loop_keywords) do
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mlp.stat:get(keyword).transformers:add (loop_transformer)
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end
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mlp.lexer:add "continue"
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mlp.stat:add{ "continue", builder = ||`Continue }
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