Control flow statements in Nim

control_flow_statements.nim

#Basic if statement
let name = readLine(stdin)
if name == "":
  echo "Poor soul, you lost your name?"
elif name == "name":
  echo "Very funny, your name is name."
else:
  echo "Hi, ", name, "!"
  
#Basic case statement
let name = readLine(stdin)
case name
of "":
  echo "Poor soul, you lost your name?"
of "name":
  echo "Very funny, your name is name."
of "Dave", "Frank":
  echo "Cool name!"
else:
  echo "Hi, ", name, "!"

#Case statement using ranges
from strutils import parseInt

echo "A number please: "
let n = parseInt(readLine(stdin))
of 0..2, 4..7: echo "The number is in the set: {0, 1, 2, 4, 5, 6, 7}"
of 3, 8: echo "The number is 3 or 8"
else: discard #do nothing

#While statement
echo "What's your name? "
var name = readLine(stdin)
while name == "":
  echo "Please tell me your name: "
  name = readLine(stdin)
  # no ``var``, because we do not declare a new variable here

#While statement mimicking for loop 
echo "Counting to 10: "
var i = 1
while i <= 10:
  echo i
  inc(i) # increment i by 1
  
#For statement
echo "Counting to ten: "
for i in countup(1, 10):
  echo i
  
echo "Counting down from 10 to 1: "
for i in countdown(10, 1):
  echo i
  
#For statement with range
for i in 1 .. 10:
  ...

#For statement with backward index operator
for i in 0 ..< 10:
  ...  # 0 .. 9

#For statement with pair() indexing
for index, item in ["a","b"].pairs:
  echo item, " at index ", index
# => a at index 0
# => b at index 1

#Explicit block statement for scoping
block myblock:
  var x = "hi"
echo x # does not work either

#Break statements
block myblock:
  echo "entering block"
  while true:
    echo "looping"
    break # leaves the loop, but not the block
  echo "still in block"
echo "outside the block"

block myblock2:
  echo "entering block"
  while true:
    echo "looping"
    break myblock2 # leaves the block (and the loop)
  echo "still in block" # it won't be printed
echo "outside the block"

#Continue statement
while true:
  let x = readLine(stdin)
  if x == "": continue
  echo x
  
  
#When statement - evaluated by compiler, useful for platform specific
when system.hostOS == "windows":
  echo "running on Windows!"
elif system.hostOS == "linux":
  echo "running on Linux!"
elif system.hostOS == "macosx":
  echo "running on Mac OS X!"
else:
  echo "unknown operating system"