Sunday, January 29, 2017

A simple language with indentation based blocks (part 0)

One of the first things I noticed when reading about Python, is the use of indentation for defining code blocks. For example:

def foo(x):
   while x < 20:
      if x > 10:
         print "argument is greater than 10"
         print "value: " + x
      else:
         print "the argument is less than or equal to 10"
         print "its value is : " + x

If you're only familiar to C-based language this seems a bit strange. Not using characters like '{}' or words like BEGIN/END seems fragile at first. For example one could expect something like:

def foo(x) {
   while x < 20 {
      if x > 10 {
         print "argument is greater than 10"
         print "value: " + x
      } else {
         print "the argument is less than or equal to 10"
         print "its value is : " + x
   }
}

I've always wondered how do you create a parser for this kind of a language. In the following series of posts I'm going to record my experiences writing a parser for a simple little language. This language will use a style similar to Python. I'm going to write the code using F# .

Posts

  1. Parsing combinators
  2. Expressions
  3. Blocks

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