Parsing/RPN to infix conversion: Difference between revisions
→{{header|M2000 Interpreter}}
SqrtNegInf (talk | contribs) m (→{{header|Perl 6}}: style tweaks) |
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Infix : ((1 + 2) ^ (3 + 4)) ^ (5 + 6)
</pre>
=={{header|Lua}}==
The ouput contains more parenthesis then in strictly nessicary, but otherwise seems to read correctly
<lang lua>function tokenize(rpn)
local out = {}
local cnt = 0
for word in rpn:gmatch("%S+") do
table.insert(out, word)
cnt = cnt + 1
end
return {tokens = out, pos = 1, size = cnt}
end
function advance(lex)
if lex.pos <= lex.size then
lex.pos = lex.pos + 1
return true
else
return false
end
end
function current(lex)
return lex.tokens[lex.pos]
end
function isOperator(sym)
return sym == '+' or sym == '-'
or sym == '*' or sym == '/'
or sym == '^'
end
function buildTree(lex)
local stack = {}
while lex.pos <= lex.size do
local sym = current(lex)
advance(lex)
if isOperator(sym) then
local b = table.remove(stack)
local a = table.remove(stack)
local t = {op=sym, left=a, right=b}
table.insert(stack, t)
else
table.insert(stack, sym)
end
end
return table.remove(stack)
end
function infix(tree)
if type(tree) == "table" then
local a = {}
local b = {}
if type(tree.left) == "table" then
a = '(' .. infix(tree.left) .. ')'
else
a = tree.left
end
if type(tree.right) == "table" then
b = '(' .. infix(tree.right) .. ')'
else
b = tree.right
end
return a .. ' ' .. tree.op .. ' ' .. b
else
return tree
end
end
function convert(str)
local lex = tokenize(str)
local tree = buildTree(lex)
print(infix(tree))
end
function main()
convert("3 4 2 * 1 5 - 2 3 ^ ^ / +")
convert("1 2 + 3 4 + ^ 5 6 + ^")
end
main()</lang>
{{out}}
<pre>3 + ((4 * 2) / ((1 - 5) ^ (2 ^ 3)))
((1 + 2) ^ (3 + 4)) ^ (5 + 6)</pre>
=={{header|M2000 Interpreter}}==
<lang M2000 Interpreter>
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