This document discusses parsing F# code with PetitParser. It focuses on indentation-sensitive features of F#, including the off-side rule where code must be indented at the same level or further than the previous line. The document presents some F# code examples and discusses challenges in building a PetitParser grammar to parse the F# syntax.

1. Parsing F# with PetitParser
F# indentation sensitive
lightweight syntax
Milan Kubicek
SCG Seminar
06.01.2015

2. some F# code..
2

3. 3
..some nicer F# code
Output:
1: 1
2: 1
3: 2
4: 3
5: 5
6: 8
7: 13
8: 21
9: 34
10: 55

4. 4
indentation
as secondary notation
indentation
as formal notation

5. indentation
in programming
secondary notation
/ syntactic sugar
define structure
F#
Python
Haskell
“curly bracket programming languages”
5
“indentation sensitive
programming languages”

6. 6
off-side rule
off-side on-side
off-side line
valid pass!
foul pass!

7. 7
off-side rule

8. 8
off-side rule
off-side on-side
off-side line

9. 9
off-side rule

10. 10
off-side rule exceptions
off-side on-side
off-side line

11. 11
off-side rule exceptions
“then-&else-body on-side aligned”
“then-body aligned”
“else-body aligned”

12. 12
challanges
F# language definition
(Petit)Parsing knowledge
mini F# PetitParser grammar
(using PetitIndent)

13. 13
F# lightweight syntax
indentation as primary notation:
..code position changes semantics!
off-side
on-side
off-side line
aligned

14. 14
questions?

15. 15

16. – http://en.wikipedia.org/wiki/Secondary_notation 05.01.2015
“…An example of secondary notation is in
computer programming, where code is often
displayed with positioning, indentation, color
and symmetry. This does not affect the
behaviour of the program, but it makes it easier
to read and understand the code…”
16
secondary notation

17. –Peter J. Landin, “The Next 700 Programming Languages”
“Any non-whitespace token to the left of the first
such token on the previous line is taken to be
the start of a new declaration.”
Off-side rule
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