109 lines
2.4 KiB
Lua
Executable file
109 lines
2.4 KiB
Lua
Executable file
#!/usr/bin/env lua
|
|
|
|
function splitTokens(s)
|
|
local tokens = {}
|
|
for i in string.gmatch(s, '%w+') do
|
|
table.insert(tokens, i)
|
|
end
|
|
return tokens
|
|
end
|
|
|
|
PLUS = 'a'
|
|
MINUS = 's'
|
|
TIMES = 'm'
|
|
DIVIDE = 'd'
|
|
|
|
function isDash(token)
|
|
return token == PLUS or token == MINUS
|
|
end
|
|
|
|
function isDot(token)
|
|
return token == TIMES or token == DIVIDE
|
|
end
|
|
|
|
function parseNum(tokens)
|
|
local val = table.remove(tokens, 1)
|
|
val = tonumber(val)
|
|
return {
|
|
['type'] = 'num',
|
|
['num'] = val
|
|
}
|
|
end
|
|
|
|
function parseFactor(tokens)
|
|
local lhs = parseNum(tokens)
|
|
while isDot(tokens[1]) do
|
|
local op = table.remove(tokens, 1)
|
|
local rhs = parseNum(tokens)
|
|
lhs = {
|
|
['type'] = 'op',
|
|
['op'] = op,
|
|
['lhs'] = lhs,
|
|
['rhs'] = rhs
|
|
}
|
|
end
|
|
return lhs
|
|
end
|
|
|
|
function parseTerm(tokens)
|
|
local lhs = parseFactor(tokens)
|
|
while isDash(tokens[1]) do
|
|
local op = table.remove(tokens, 1)
|
|
local rhs = parseFactor(tokens)
|
|
lhs = {
|
|
['type'] = 'op',
|
|
['op'] = op,
|
|
['lhs'] = lhs,
|
|
['rhs'] = rhs,
|
|
}
|
|
end
|
|
return lhs
|
|
end
|
|
|
|
function parseExpr(tokens)
|
|
return parseTerm(tokens)
|
|
end
|
|
|
|
function eval(expr)
|
|
if expr['type'] == 'num' then
|
|
return expr['num']
|
|
elseif expr['type'] == 'op' then
|
|
local lval = eval(expr['lhs'])
|
|
local rval = eval(expr['rhs'])
|
|
if expr['op'] == PLUS then
|
|
return lval + rval
|
|
elseif expr['op'] == MINUS then
|
|
return lval - rval
|
|
elseif expr['op'] == TIMES then
|
|
return lval * rval
|
|
elseif expr['op'] == DIVIDE then
|
|
return lval / rval
|
|
else
|
|
print('invalid operator!')
|
|
end
|
|
else
|
|
print('invalid expr type!')
|
|
end
|
|
end
|
|
|
|
function printTree(expr, depth)
|
|
local indent = string.rep(' ', depth)
|
|
print(indent .. 'type: ' .. expr['type'])
|
|
if expr['type'] == 'num' then
|
|
print(indent .. 'num: ' .. expr['num'])
|
|
elseif expr['type'] == 'op' then
|
|
print(indent .. 'op: ' .. expr['op'])
|
|
print(indent .. 'lhs:')
|
|
printTree(expr['lhs'], depth + 1)
|
|
print(indent .. 'rhs:')
|
|
printTree(expr['rhs'], depth + 1)
|
|
else
|
|
print('invalid expr type!')
|
|
end
|
|
end
|
|
|
|
tree = parseExpr(splitTokens(arg[1]))
|
|
print('tree:')
|
|
printTree(tree, 0)
|
|
print('result: ' .. eval(tree))
|
|
|