add math.lua example

1 files changed, 63 insertions, 0 deletions

diff --git a/examples/math.lua b/examples/math.lua
new file mode 100644
index 0000000..eed979b
--- /dev/null
+++ b/examples/math.lua
@@ -0,0 +1,63 @@
+local patok   = require 'patok'
+local inspect = require 'inspect'
+local pm      = require 'piecemeal'
+
+local lexer = patok {
+	op    = '[+*]',
+	digit = '%d+',
+	space = '%s+',
+}()
+
+local lex = {
+	-- plus  = pm.lexeme 'plus',
+	plus  = pm.value '+',
+	times = pm.value '*',
+	digit = pm.postp(pm.lexeme 'digit', function(d) return tonumber(d.value) end),
+	space = pm.opt(pm.lexeme 'space')
+}
+
+local function findnums(d, acc)
+	local out = acc or {}
+	for _, v in ipairs(d) do -- only ipairs to avoid triggering on tokens
+		if type(v) == 'number' then
+			table.insert(out, v)
+		elseif type(v) == 'table' then
+			findnums(v, out)
+		end
+	end
+	return out
+end
+
+local mult = pm.postp(
+	pm.all(lex.digit, pm.star(pm.all(lex.space, lex.times, lex.space, lex.digit))),
+	function (d)
+		local acc = 1
+		for _, v in ipairs(findnums(d)) do
+			acc = acc * v
+		end
+		return acc
+	end)
+	
+local add = pm.postp(
+	pm.all(mult, pm.star(pm.all(lex.space, lex.plus, lex.space, mult))),
+	function (d)
+		local acc = 0
+		for _, v in ipairs(findnums(d)) do
+			acc = acc + v
+		end
+		return acc
+	end)
+
+local expr = add
+
+local test
+if arg[1] then
+	local f = io.open(arg[1], 'r')
+	test = f:read '*a'
+	f:close()
+else
+	test = [[10 + 5 * 2 + 10]]
+end
+
+local eind, out = pm.parse(test, lexer, expr)
+print(eind, out)