Parsing out

a Good Parser

Parsing Parsers Outline

Why Parse and What is a Parser
Ways to Parse and What we will Parse
Attempt #1 Regroup and Try Again #2
Try #3 has got to work
Never Give Up the Ghost #4
What Works and What to Watch Out for

Why Parse

people cannot understand binary data
computers cannot understand people
a parser translates from 'people' to 'computer'
people are less than perfect in writing text
computers require structural perfection

What is a Parser

program to convert text into binary data
but not any text, the text has to follow a grammar
a grammar is a set of rules (we'll code these up soon)
the binary data is also called an Abstract Syntax Tree (AST)

Parts of a Parser

Lexer (optional)
A parser generator (grammar compiler) OR a runtime library
Actions: functions that translate to the Abstract Syntax Tree (AST) elements of your choice

All the Ways to Parse

regular expressions (v)
parser generators using PEG files
hand coded (recursive decent) parsers
parser combinators
others

(techniques)

What to Parse

identifiers
strings "in quotes"
lists (of identifiers, strings and of course nested lists)
comments

a modest wish list

Test

Driven

Demo

https://github.com/nmorse/set-parsers-to-stun

canopy

parser generator for languages [python java javascript ruby]

nearley

generates javascript

also generates RR diagrams

a hand coded parser

with the help of xState (a finite state machine lib)

arcsecond

A set of parser "combinators"

(functions that take other functions as arguments and return (yes) new functions)

Compose them (combine them) into a parser

	canopy	nearley	hand code	arcsecond
learning curve	+1	+3	-2	-1
features	+1	+3	0	+3
friendly errors	0	0	+1	+1
following	-1	+3	0	+2
bottom line	+1	+9	-1	+5

What Works and What to Watch Out for

Thank You