--- Extract delimited Lua sequences from strings. -- Inspired by Damian Conway's Text::Balanced in Perl.
--
--
-- local lb = require "pl.luabalanced"
-- --Extract Lua expression starting at position 4.
--  print(lb.match_expression("if x^2 + x > 5 then print(x) end", 4))
--  --> x^2 + x > 5     16
-- --Extract Lua string starting at (default) position 1.
-- print(lb.match_string([["test\"123" .. "more"]]))
-- --> "test\"123"     12
-- 
-- (c) 2008, David Manura, Licensed under the same terms as Lua (MIT license). -- @class module -- @name pl.luabalanced local M = {} local assert = assert -- map opening brace <-> closing brace. local ends = { ['('] = ')', ['{'] = '}', ['['] = ']' } local begins = {}; for k,v in pairs(ends) do begins[v] = k end -- Match Lua string in string starting at position . -- Returns , , where is the matched -- string (or nil on no match) and is the character -- following the match (or on no match). -- Supports all Lua string syntax: "...", '...', [[...]], [=[...]=], etc. local function match_string(s, pos) pos = pos or 1 local posa = pos local c = s:sub(pos,pos) if c == '"' or c == "'" then pos = pos + 1 while 1 do pos = assert(s:find("[" .. c .. "\\]", pos), 'syntax error') if s:sub(pos,pos) == c then local part = s:sub(posa, pos) return part, pos + 1 else pos = pos + 2 end end else local sc = s:match("^%[(=*)%[", pos) if sc then local _; _, pos = s:find("%]" .. sc .. "%]", pos) assert(pos) local part = s:sub(posa, pos) return part, pos + 1 else return nil, pos end end end M.match_string = match_string -- Match bracketed Lua expression, e.g. "(...)", "{...}", "[...]", "[[...]]", -- [=[...]=], etc. -- Function interface is similar to match_string. local function match_bracketed(s, pos) pos = pos or 1 local posa = pos local ca = s:sub(pos,pos) if not ends[ca] then return nil, pos end local stack = {} while 1 do pos = s:find('[%(%{%[%)%}%]\"\']', pos) assert(pos, 'syntax error: unbalanced') local c = s:sub(pos,pos) if c == '"' or c == "'" then local part; part, pos = match_string(s, pos) assert(part) elseif ends[c] then -- open local mid, posb if c == '[' then mid, posb = s:match('^%[(=*)%[()', pos) end if mid then pos = s:match('%]' .. mid .. '%]()', posb) assert(pos, 'syntax error: long string not terminated') if #stack == 0 then local part = s:sub(posa, pos-1) return part, pos end else stack[#stack+1] = c pos = pos + 1 end else -- close assert(stack[#stack] == assert(begins[c]), 'syntax error: unbalanced') stack[#stack] = nil if #stack == 0 then local part = s:sub(posa, pos) return part, pos+1 end pos = pos + 1 end end end M.match_bracketed = match_bracketed -- Match Lua comment, e.g. "--...\n", "--[[...]]", "--[=[...]=]", etc. -- Function interface is similar to match_string. local function match_comment(s, pos) pos = pos or 1 if s:sub(pos, pos+1) ~= '--' then return nil, pos end pos = pos + 2 local partt, post = match_string(s, pos) if partt then return '--' .. partt, post end local part; part, pos = s:match('^([^\n]*\n?)()', pos) return '--' .. part, pos end -- Match Lua expression, e.g. "a + b * c[e]". -- Function interface is similar to match_string. local wordop = {['and']=true, ['or']=true, ['not']=true} local is_compare = {['>']=true, ['<']=true, ['~']=true} local function match_expression(s, pos) pos = pos or 1 local _ local posa = pos local lastident local poscs, posce while pos do local c = s:sub(pos,pos) if c == '"' or c == "'" or c == '[' and s:find('^[=%[]', pos+1) then local part; part, pos = match_string(s, pos) assert(part, 'syntax error') elseif c == '-' and s:sub(pos+1,pos+1) == '-' then -- note: handle adjacent comments in loop to properly support -- backtracing (poscs/posce). poscs = pos while s:sub(pos,pos+1) == '--' do local part; part, pos = match_comment(s, pos) assert(part) pos = s:match('^%s*()', pos) posce = pos end elseif c == '(' or c == '{' or c == '[' then _, pos = match_bracketed(s, pos) elseif c == '=' and s:sub(pos+1,pos+1) == '=' then pos = pos + 2 -- skip over two-char op containing '=' elseif c == '=' and is_compare[s:sub(pos-1,pos-1)] then pos = pos + 1 -- skip over two-char op containing '=' elseif c:match'^[%)%}%];,=]' then local part = s:sub(posa, pos-1) return part, pos elseif c:match'^[%w_]' then local newident,newpos = s:match('^([%w_]+)()', pos) if pos ~= posa and not wordop[newident] then -- non-first ident local pose = ((posce == pos) and poscs or pos) - 1 while s:match('^%s', pose) do pose = pose - 1 end local ce = s:sub(pose,pose) if ce:match'[%)%}\'\"%]]' or ce:match'[%w_]' and not wordop[lastident] then local part = s:sub(posa, pos-1) return part, pos end end lastident, pos = newident, newpos else pos = pos + 1 end pos = s:find('[%(%{%[%)%}%]\"\';,=%w_%-]', pos) end local part = s:sub(posa, #s) return part, #s+1 end M.match_expression = match_expression -- Match name list (zero or more names). E.g. "a,b,c" -- Function interface is similar to match_string, -- but returns array as match. local function match_namelist(s, pos) pos = pos or 1 local list = {} while 1 do local c = #list == 0 and '^' or '^%s*,%s*' local item, post = s:match(c .. '([%a_][%w_]*)%s*()', pos) if item then pos = post else break end list[#list+1] = item end return list, pos end M.match_namelist = match_namelist -- Match expression list (zero or more expressions). E.g. "a+b,b*c". -- Function interface is similar to match_string, -- but returns array as match. local function match_explist(s, pos) pos = pos or 1 local list = {} while 1 do if #list ~= 0 then local post = s:match('^%s*,%s*()', pos) if post then pos = post else break end end local item; item, pos = match_expression(s, pos) assert(item, 'syntax error') list[#list+1] = item end return list, pos end M.match_explist = match_explist -- Replace snippets of code in Lua code string -- using replacement function f(u,sin) --> sout. -- is the type of snippet ('c' = comment, 's' = string, -- 'e' = any other code). -- Snippet is replaced with (unless is nil or false, in -- which case the original snippet is kept) -- This is somewhat analogous to string.gsub . local function gsub(s, f) local pos = 1 local posa = 1 local sret = '' while 1 do pos = s:find('[%-\'\"%[]', pos) if not pos then break end if s:match('^%-%-', pos) then local exp = s:sub(posa, pos-1) if #exp > 0 then sret = sret .. (f('e', exp) or exp) end local comment; comment, pos = match_comment(s, pos) sret = sret .. (f('c', assert(comment)) or comment) posa = pos else local posb = s:find('^[\'\"%[]', pos) local str if posb then str, pos = match_string(s, posb) end if str then local exp = s:sub(posa, posb-1) if #exp > 0 then sret = sret .. (f('e', exp) or exp) end sret = sret .. (f('s', str) or str) posa = pos else pos = pos + 1 end end end local exp = s:sub(posa) if #exp > 0 then sret = sret .. (f('e', exp) or exp) end return sret end M.gsub = gsub return M