# Learning #9: The APOP Programming Language

Believe it or not, I changed my mind again. I know, I know, I know… stick to one thing.

However, I just could not get myself to reimplement another version of the semi-object-oriented Sailfish Programming Language. It is so boring and it’s really time to try a LISP.

So, without further ado, I present APOP. APOP stands for (A) (P)lethora (O)f (P)arentheses. This language will start extremely simple, basically an implementation of the simplified version of Scheme used in The Little Lisper and then will expand once I am 100% sure it actually works correctly (versus Sailfish which never has worked 100% correctly, or even 80% correctly).

## Grammar and Such

Instead of just banging away at the keys (a skill I have picked up from work), I decided it would be best to get my thoughts down on paper (read markdown). Thus, today I wrote out a rough draft of the grammar, the lexicon, and some of the foundational functions that will ship with the APOP compiler.

### Lexicon

Quoted from the APOP docs:

The Lexicon of APOP consists of all the characters common in English, uppercase and lowercase, all number characters, parenthesis, a question mark only if it is prefaced by at least one character and followed by a whitespace, and finally hashmarks only if followed by a ‘t’ or a ‘f’.

The following are keywords:

• def
• lambda
• cond

### Grammar

This grammar may seem overlysimplified… and it might be. I will see how this actually plays out when I get to implementing it (for Sailfish I changed the grammar considerably when I realized my first, second, and third drafts were not actually implementable in any shape or form).

Data := [Atom | List]

Definition := 'define' Data
Lambda := 'lambda' Data
Conditional := 'cond' Data

Atom := ''' [AlphaNumeric | Empty | List]
AlphaNumeric := Alpha | Numeric
Alpha        := [A-z][A-z?]*
Numeric      := [0-9]*
List         := '(' Data ')'

Boolean      := #t | #f


### Foundational Functions

I could only come up with a couple of these to start. However, there is no rush to figure this out… this is a very post backend sort of step.

So far what I have is:
cons: combine two elements
car: return the first element from a list
eq?: determine whether two bits of data are the same

And that is about all I have today – spent much longer on the blog post and learnings than I should have (and 30 minutes were wasted picking the name) 🤷. Off to the gym!