author: niplav, created: 2022-01-08, modified: 2022-01-08, language: english, status: in progress, importance: 2, confidence: likely
Solutions to the book “Programming in Lua” by Roberto Ierusalimschy.
function fact(n)
elseif n==0 then
return 1
else
return n * fact(n-1)
end
end
print("enter a number:")
a=io.read("*n")
print(fact(a))
For a script that loads a library the dofile option is probably preferable, since then there is no need to deal with the different ways different platforms handle flags, when using lua interactively, the '-l' option is nicer, since one needs to type less.
Actually, from the top of my head, I really can't. But apparently, Haskell does it, which is weird, since Lua and Haskell have pretty different lineages afaik.
Valid identifiers from the list: ___, _end, End, NULL
Invalid identifiers: end, until?, nil
#!/usr/bin/lua
print(arg[0])
Then, update the permissions (on a unix-based system):
$ chmod 0755 ex_5.lua
The result of the expression type(nil)==nil is false, since the type
of type(nil) is string, and the string "nil" is not equal to the
value nil.
Invalid numerals: .e12, 0.0e, 0xABFG, FFFF, 0x
Valid numerals (with value): .0e12 -> 0.0, 0x12 -> 18, 0xA ->
10, 0xFFFFFFFF -> 4294967295, 0x1P10 -> 1024, 0.1e1 -> 1.0,
0x0.1p1 -> 0.125
12.7 can't be represented by
(n*12.7)/2^m
but 5.5 can be represented by
11/2^1
a="<![CDATA[\n Hello world\n]]>"
b=[=[
<![CDATA[
Hello world
]]>]=]
One good way to format the sequence of bytes would be to display it in a
string with escaped bytes in hexadecimal format, split into several lines
with "\z". By doing this problems with line length can be avoided and
performance is probably not very bad, considering that computers handle
byte sequences considerably well. Readability can, but should not be a
problem, since when dealing with arbitrary byte sequences the value in
hexadecimal is used more frequently than the ASCII value.
a={}
a.a=a
a.a.a.a evaluates to the table a the first a is a pointer to the
table a, the other as are all keys the expression can be rewritten as
a["a"]["a"]["a"]
a.a.a.a=3
Now the value for the key "a" is 3 in the table a, so a.a is 3,
and a.a.a is not indexable, since 3 has no field called "a". So Lua
prints an error message.
-10 2
-9 0
-8 1
-7 2
-6 0
-5 1
-4 2
-3 0
-2 2
-1 1
0 0
1 1
2 2
3 0
4 1
5 2
6 0
7 1
8 2
9 0
10 1
2^3^4=2^(3^4)=1.4178e+24
2^-3^4=(2^(-(3^4))=4.1359e-25
function polyeval(a, x)
local res=0
for i=1, #a do
res=res+a[i]*x^(i-1)
end
return res
end
function polyeval(a, x)
local res=0
for i=1, #a do
res=res*x
res=res+a[i]
end
return res
end
function isbool(v)
return v==true or v==false
end
The parentheses are not necessary, since not binds stronger than
and, and and binds stronger than or. However, the parentheses are
probably still a good idea, since they make the expression easier to
read and understand.
monday sunday sunday
One way to initialize the table would be to use the square bracket
notation. Associating the escape sequence "\a" with the literal bell
character would be done like this:
{["\\a"]="\a"}
This would be done for every escape sequence.
In Lua there is no switch/case statement, so elseif is a necessary (albeit not sufficient) replacement.
Preferred method is the first one, since it doesn't deal with limits and makes an infinite loop clear from the beginning.
while true do end
for i=0, math.huge do end
for i=2, 1, 0 do end
repeat until false
repeat-until is a construct similar to do-while in C, a construct which is also used rarely there. Apparently, in C only 5% of loops in C code are do-while loops. However, repeat-until can be useful to avoid initializing a variable the same way it is incremented in the loop, saving one line. It makes elegant solutions easier, but not much beyond that, so it could be left out easily.
local z = 0
local c
repeat
c = io.read()
if c == '0' then z=z+1 end
print(z)
until c == nil
if z % 2 == 0 then
print('ok')
else
print('not ok')
end
Jumping out of a function would jump into the scope of a local variable, which is not possible (per definition) in Lua.
This would also cause problems in a function calling itself and jumping back into itself (or two different functions calling each other recursively), since there would be no good way to determine whether the goto would simply jump inside the function or outside into a previous call of itself.
The program would first print:
10
9
8
7
6
5
4
3
2
1
and then return an anonymous function that jumps to the end of getlabel() and return 0.
function concat(...)
local args={...}
local r=""
for i, v in ipairs(args) do
r=r..v
end
return r
end
function printarr(arr)
print(table.unpack(arr))
end
function allbutone(...)
local r={}
local args=table.pack(...)
for i=2, args.n do
r[i-1]=args[i]
end
return table.unpack(r)
end
function combi(t, n)
local arg={}
local res={}
local save={}
if n<=0 then
return {{}}
end
for k, v in ipairs(t) do save[k]=v end
while #save>0 do
local last=save[#save]
save[#save]=nil
for k, v in ipairs(save) do table.insert(arg, v) end
local tmp=combi(arg, n-1)
arg={}
for i=1, #tmp do table.insert(tmp[i], last) end
for k, v in ipairs(tmp) do table.insert(res, v) end
end
return res
end
function comb(t)
local res={}
for i=1, #t do
tmp=combi(t, i)
for k, v in ipairs(tmp) do table.insert(res, tmp[k]) end
end
return res
end
function integral(f)
return function(x, y)
local i, res, eps
res=0; eps=0.001
for i=x, y, eps do
res=res+f(i)*eps
end
return res
end
end
function newpoly(t)
return function(x)
local res=0
for i=1, #t do
res=res+t[i]*x^(#t-i)
end
return res
end
end
n=100000
function f()
print(n)
n=n-1
if n<0 then
return nil
else
return "i=1;"
end
end
load(f)()
function room1()
local move=io.read()
if move=="south" then room3()
elseif move=="east" then room2()
else
print("invalid move")
room1()
end
end
function room2()
local move=io.read()
if move=="south" then room4()
elseif move=="west" then room1()
else
print("invalid move")
room2()
end
end
function room3()
local move=io.read()
if move=="north" then room1()
elseif move=="east" then room4()
else
print("invalid move")
room3()
end
end
function room4()
print("Congrats, asshat. You won.")
end
room1()
function fromto(n, m)
return fromit, {m}, n-1
end
function fromit(t, v)
if v<t[1] then
return v+1
else
return nil
end
end
function fromto(n, m, s)
return fromit, {m, s}, n-s
end
function fromit(t, v)
if v+t[2]<=t[1] then
return v+t[2]
else
return nil
end
end
function uniquewords()
local line=io.read()
local wordtable={}
local pos=1
wordtable[""]=1
return function()
local str=""
local s, e
repeat
s, e=string.find(line, "%w+", pos)
if s then
pos=e+1
str=str.sub(line, s, e)
else
line=io.read()
pos=1
end
until not line or wordtable[str]~=1
wordtable[str]=1
return (line and str) or nil
end
end
function substrings(s)
local len, pos
len=0
pos=1
return function()
if pos+len>#s then
pos=pos+1
len=0
end
if pos>#s then
return nil
else
local str=string.sub(s, pos, pos+len)
len=len+1
return str
end
end
end
s is definitely a string, c can be a string or a function
function loadwithprefix(s, c)
return load(function ()
local t
if s then
t=s
s=nil
elseif type(c)=="string" then
t=c
c=nil
elseif type(c)=="function" then
t=c()
end
return t
end)
end
function multiload(...)
local t=table.pack(...)
local i=1
return load(function ()
local res
if i>#t then
return nil
end
if type(t[i])=="string" then
i=i+1
return t[i-1]
end
while not res and i<=#t do
res=t[i]()
i=i+1
end
return res
end)
end
The two functions have nearly the same speed.
function stringrep_n(n)
local res=[[ s=...
local r=""
]]
if n>0 then
while n>1 do
if n%2~=0 then res=res .. "\tr=r .. s\n" end
res=res .. "\ts=s .. s\n"
n=math.floor(n/2)
end
res=res .. "\tr=r .. s\n"
end
res=res .. "\treturn r\n"
return load(res)
end
Shamelessly stolen (years later, I don't know where from, though :-D):
function f()
count = 0
function g()
count = count + 1
if count == 2 then debug.sethook() end
error()
end
debug.sethook(g, "r")
end
with
pcall(pcall, f)
returns false, nil.
function combgen(t, n, r, i)
local idx=i or 1
local res=r or {}
if n<=0 then
coroutine.yield(res)
else
for j=idx, #t-n do
res[n]=t[j]
combgen(t, n-1, res, j+1)
end
end
end
function combinations(t, n)
return coroutine.wrap(function() combgen(t, n) end)
end
socket=require("socket")
function download(host, file)
local c=assert(socket.connect(host, 80))
local count=0
c:send("GET " .. file .. " HTTP/1.0\r\n\r\n")
while true do
local s, status=receive(c)
count=count+#s
if status=="closed" then break end
end
c:close()
print(file, count)
end
function receive(connection)
connection:settimeout(0)
local s, status, partial=connection:receive(2^10)
if status=="timeout" then
coroutine.yield(connection)
end
return s or partial, status
end
function get(host, file)
local co=coroutine.create(function()
download(host, file)
end)
table.insert(threads, co)
end
function dispatch()
local i=1
local timedout={}
while true do
if threads[i]==nil then
if threads[1]==nil then break end
i=1
timedout={}
end
local status, res=coroutine.resume(threads[i])
if not res then
table.remove(threads, i)
else
i=i+1
timedout[#timedout+1]=res
if #timedout==#thredas then
socket.select(timedout)
end
end
end
end
threads={}
function transfer(cr)
coroutine.yield(cr)
end
function dispatch(b)
nr=coroutine.create(b)
while nr~=nil do
nr=coroutine.resume(nr)
end
end
local N=8
local function isplaceok(a, n, c)
for i=1, n-1 do
if (a[i]==c) or
(a[i]-i==c-n) or
(a[i]+i==c+n) then
return false
end
end
return true
end
local function printsolution(a)
for i=1, N do
for j=1, N do
io.write(a[i]==j and "X" or "-", " ")
end
io.write("\n")
end
io.write("\n")
os.exit()
end
local function addqueen(a, n)
if n>N then
printsolution(a)
else
for c=1, N do
if isplaceok(a, n, c) then
a[n]=c
addqueen(a, n+1)
end
end
end
end
addqueen({}, 1)
local N=8
function permgen(a, n)
n=n or #a
if n<=1 then
coroutine.yield(a)
else
for i=1, n do
a[n], a[i]=a[i], a[n]
permgen(a, n-1)
a[n], a[i]=a[i], a[n]
end
end
end
function permutations(a)
return coroutine.wrap(function() permgen(a) end)
end
local function isplaceok(a, n, c)
for i=1, n-1 do
if (a[i]==c) or
(a[i]-i==c-n) or
(a[i]+i==c+n) then
return false
end
end
return true
end
local function printsolution(a)
for i=1, N do
for j=1, N do
io.write(a[i]==j and "X" or "-", " ")
end
io.write("\n")
end
io.write("\n")
end
for q in permutations({1, 2, 3, 4, 5, 6, 7, 8}) do
local i=1
while i<N+1 and isplaceok(q, i, q[i]) do i=i+1 end
if i==N+1 then printsolution(q) end
end
local function allwords()
local auxwords=function()
for line in io.lines() do
for word in string.gmatch(line, "%w+") do
coroutine.yield(word)
end
end
end
return coroutine.wrap(auxwords)
end
local counter={}
for w in allwords() do
if #w>=4 then
counter[w]=(counter[w] or 0) + 1
end
end
local words={}
for w in pairs(counter) do
words[#words+1]=w
end
table.sort(words, function(w1, w2)
return counter[w1]>counter[w2] or
counter[w1]==counter[w2] and w1<w2
end)
for i=1, (tonumber(arg[1]) or 10) do
print(words[i], counter[words[i]])
end
local N=3
function allwords()
local line=io.read()
local pos=1
return function()
while line do
local s, e=string.find(line, "%w+", pos)
if s then
pos=e+1
return string.sub(line, s, e)
else
line=io.read()
pos=1
end
end
return nil
end
end
function prefix(p)
local s=p[1]
for i=2, #p do s=s .. " " .. p[i] end
return s
end
function back(p)
for i=1, N-1 do p[i]=p[i+1] end
end
local statetab={}
function insert(index, value)
local list=statetab[index]
if list==nil then
statetab[index]={value}
else
list[#list+1]=value
end
end
local MAXGEN=10000
local NOWORD="\n"
pf={}
for i=1, N do pf[i]=NOWORD end
for w in allwords() do
insert(prefix(pf), w)
back(pf)
pf[N]=w
end
insert(prefix(pf), NOWORD)
for i=1, N do pf[i]=NOWORD end
for i=1, MAXGEN do
local ls=statetab[prefix(pf)]
local r=math.random(#ls)
local nextword=ls[r]
if nextword==NOWORD then return end
io.write(nextword, " ")
back(pf)
pf[N]=nextword
end
It's stupid to set both values to 0. This just restores the first state.
queue={}
function queue.new()
return {first=0, last=-1}
end
function queue.pushfirst(q, value)
q[q.first]=value
q.first=q.first+1
end
function queue.pushlast(q, value)
q[q.last]=value
q.last=q.last-1
end
function queue.popfirst(q)
local first=q.first-1
if q.last>first then error("queue is empty") end
local value=q[first]
q[first]=nil
q.first=first
if q.last>=q.first-1 then q.first=0; q.last=-1 end
return value
end
function queue.poplast(q)
local last=q.last+1
if last>q.first then error("queue is empty") end
local value=q[last]
q[last]=nil
q.last=last
if q.last>=q.first-1 then q.first=0; q.last=-1 end
return value
end
Using a closure for the allwords argument
local function allwords(f)
local auxwords=function()
for line in io.lines(f) do
for word in string.gmatch(line, "%w+") do
coroutine.yield(word)
end
end
end
return coroutine.wrap(auxwords)
end
local ignore={}
for w in allwords(arg[2] or "ignore") do
ignore[w]=true
end
local counter={}
for w in allwords() do
if not ignore[w] then
counter[w]=(counter[w] or 0) + 1
end
end
local words={}
for w in pairs(counter) do
words[#words+1]=w
end
table.sort(words, function(w1, w2)
return counter[w1]>counter[w2] or
counter[w1]==counter[w2] and w1<w2
end)
for i=1, (tonumber(arg[1]) or 10) do
print(words[i], counter[words[i]])
end
function name2node(graph, name)
local node=graph[name]
if not node then
node={name=name, adj={}}
graph[name]=node
end
return node
end
function readgraph(f)
local graph={}
for line in io.lines(f) do
local namefrom, nameto, label=string.match(line, "(%S+)%s+(%S+)%s+(%d+)")
local from=name2node(graph, namefrom)
local to=name2node(graph, nameto)
from.adj[to]=label
end
return graph
end
function findpath(curr, to, path, visited)
path=path or {}
visited=visited or {}
if visited[curr] then
return nil
end
visited[curr]=true
path[#path+1]=curr
if curr==to then
return path
end
for node in pairs(curr.adj) do
local p=findpath(node, to, path, visited)
if p then return p end
end
path[#path]=nil
end
function printpath(path)
for i=1, #path do
print(path[i].name)
end
end
dofile("ex_3.lua")
function dijkstra(g, s, e)
local unvisited={}
local dist={}
local prev={}
local start=g[s]
local lst=g[e]
local current=start
for i, j in pairs(g) do unvisited[j]=true end
for i, j in pairs(g) do dist[j]=math.huge end
dist[start]=0
while current~=lst do
for to, l in pairs(current.adj) do
if unvisited[to]==true then
local ndist=dist[current]+l
if dist[to]>ndist then
dist[to]=ndist
prev[to]=current
end
end
end
unvisited[current]=false
current=lst
for i, j in pairs(unvisited) do
if j==true and dist[i]<dist[current] then
current=i
end
end
end
return prev
end
g: the graphs: the name of the starting pointe: the name of the endpoint
function serialize(o, l)
l=l or 1
if type(o)=="number" then
io.write(string.format("%a", o))
elseif type(o)=="string" then
io.write(string.format("%q", o))
elseif type(o)=="table" then
io.write("{\n")
for k, v in pairs(o) do
io.write(string.rep("\t", l))
serialize(k, l+1)
io.write("=")
serialize(v, l+1)
io.write(",\n")
end
io.write(string.rep("\t", l-1) .. "}")
if l==1 then io.write("\n") end
else
error("cannot serialize a " .. type(o))
end
end
function serialize(o, l)
l=l or 1
if type(o)=="number" then
io.write(string.format("%a", o))
elseif type(o)=="string" then
io.write(string.format("%q", o))
elseif type(o)=="table" then
io.write("{\n")
for k, v in pairs(o) do
io.write(string.rep("\t", l) .. "[")
serialize(k, l+1)
io.write("] = ")
serialize(v, l+1)
io.write(",\n")
end
io.write(string.rep("\t", l-1) .. "}")
if l==1 then io.write("\n") end
else
error("cannot serialize a " .. type(o))
end
end
function serialize(o, l)
l=l or 1
if type(o)=="number" then
io.write(string.format("%a", o))
elseif type(o)=="string" then
io.write(string.format("%q", o))
elseif type(o)=="table" then
io.write("{\n")
for k, v in pairs(o) do
io.write(string.rep("\t", l))
if type(k)~="string" or not isidentifier(k) then io.write("[") end
if type(k)=="string" and isidentifier(k) then io.write(k)
else serialize(k, l+1) end
if type(k)~="string" or not isidentifier(k) then io.write("]") end
io.write(" = ")
serialize(v, l+1)
io.write(",\n")
end
io.write(string.rep("\t", l-1) .. "}")
if l==1 then io.write("\n") end
else
error("cannot serialize a " .. type(o))
end
end
function isidentifier(s)
return string.match(s, "^[a-zA-Z_][a-zA-Z0-9_]*$")
end
function serialize(o, l)
l=l or 1
if type(o)=="number" then
io.write(string.format("%a", o))
elseif type(o)=="string" then
io.write(string.format("%q", o))
elseif type(o)=="table" then
local i=1
io.write("{\n")
if o[i]~=nil then
io.write(string.rep("\t", l))
while o[i]~=nil do serialize(o[i]); io.write(", "); i=i+1 end
io.write("\n")
end
for k, v in pairs(o) do
if type(k)~="number" or k<1 or k>i then
io.write(string.rep("\t", l))
if type(k)~="string" or not isidentifier(k) then io.write("[") end
if type(k)=="string" and isidentifier(k) then io.write(k)
else serialize(k, l+1) end
if type(k)~="string" or not isidentifier(k) then io.write("]") end
io.write(" = ")
serialize(v, l+1)
io.write(",\n")
end
end
io.write(string.rep("\t", l-1) .. "}")
if l==1 then io.write("\n") end
else
error("cannot serialize a " .. type(o))
end
end
function isidentifier(s)
return string.match(s, "^[a-zA-Z_][a-zA-Z0-9_]*$")
end