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--[[
A parser has the signature: (list, sindex) -> eindex [, output]
If the parser "fails", it must return exactly nil.
If the parser "succeeds", it must return at least the eindex, and may also return some output.
]]--
return {
eof = function ()
return function (l, i)
-- we don't have to, but we advance the pointer by one
-- this prevents infinite looping
if #l+1 == i then
local pos = l[#l].stop + 1
return i+1, {type = 'EOF', value = '', start = pos, stop = pos}
end
return nil
end
end,
lexeme = function (type)
return function (l, i)
if l[i] and l[i].type == type then
return i+1, l[i]
end
return nil
end
end,
value = function (value)
return function (l, i)
if l[i] and l[i].value == value then
return i+1, l[i]
end
return nil
end
end,
all = function (...)
local args = {...}
return function (l, i)
local res = {}
local eind, out
for _, v in ipairs(args) do
eind, out = v(l, i)
if not eind then return nil end
i = eind
table.insert(res, out)
end
return i, res
end
end,
alt = function (...)
local args = {...}
return function (l, i)
local eind, out
for _, v in ipairs(args) do
eind, out = v(l, i)
if eind then
return eind, out
end
end
return nil
end
end,
opt = function (p)
return function (l, i)
local eind, out = p(l, i)
if eind
then return eind, out
else return i
end
end
end,
plus = function (p)
return function (l, i)
local res = {}
local eind, out = p(l, i)
if not eind then return nil end
repeat
i = eind
table.insert(res, out)
eind, out = p(l, i)
until not eind
return i, res
end
end,
star = function (p)
return function (l, i)
local res = {}
local eind, out
repeat
eind, out = p(l, i)
if eind then
table.insert(res, out)
i = eind
end
until not eind
return i, res
end
end,
postp = function (p, f)
return function (l, i)
local eind, out = p(l, i)
if out then out = f(out) end
return eind, out
end
end,
parse = function (text, lexer, parser)
local tokens = {}
lexer:reset(text)
local next
repeat
next = lexer:next()
if next then table.insert(tokens, next) end
until next == nil
local eind, out = parser(tokens, 1)
-- a successful parse means eind is > the length of tokens
if eind > #tokens then
return out, tokens[#tokens].stop, nil
else -- TODO: what if eind == 1? can that happen?
return out, tokens[eind-1].stop, tokens[eind].start
end
end,
}
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