# Building the parser

## Install node

We need to use node:

apt-get install node npm


Inside stack/stack/maximaparser (or anywhere else), and not as root

npm install pegjs
npm install phpegjs ts-pegjs


## Compile the parser

To compile the parser

node gen.js


This should return null null null and create new parsers for STACK.

## Adding rules to the parser

Identical changes need to be made in both

1. stack/maximaparser/MP_classes.php
2. stack/maximaparser/autogen/parser-grammar.pegjs

## Naming parser rules

We give each parser rule a name, numbered in the approximate appropriate order in which they need to be applied.

• 0-10 the mandatory stars for "f(x)(y) => f(x)*(y)" and syntactical candy like the logarithms
• 10-20 rules forbidding certain usages.
• 20-30 identification of typical syntax mistakes like "sin^2(x)".
• 30-40 rules forbidding certain usages, like calling functions at all.
• 40-50 various rules adding stars, insert stars in function calls and split variables and whatnot.
• 60-70 rules forbidding certain usages, e.g. forbid floats.
• 80-90 logic to check for things that have been done and deciding whether what was done was ok i.e. stars were inserted but not allowed in "syntax=true".

## Debugging the parser rules

echo "\n" . $ast->debugPrint($ast->toString() . '     ') . "\n";
while ($ast->callbackRecurse($process, true) !== true) {
echo "\n" . $ast->debugPrint($ast->toString() . '     ') . "\n";
}
echo "\n" . $ast->debugPrint($ast->toString() . '     ') . "\n";


# Nouns

There are two separate classes of expressions which need to be protected as "nouns".

1. The Maxima Boolean functions do not respect simp:false. So, we have parallel operators such as A nounand B. These should always be used when connecting to Maxima. Evaluation/simplification of Boolean expressions such as true and false is done on the Maxima side. Teachers and students should use and, etc. and these are always translated into an evaluation form.
2. With simp:false we still have evaluation of expressions such as diff(x^3,x) to 3*x^2. To protect student's answers ("Your last answer was..") we have parallel noun forms such as noundiff and nounint. Note, some of these also change the display of expressions.
3. Maxima uses the apostophie to create noun forms, e.g. 'diff(x^3,x). From STACK 4.3, teachers are able to use this.