Showing Revision 3 created 05/25/2016 by Udacity Robot.

1. Title:
   Parsing Javascript Expressions Solution - Programming Languages
2. Description:

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   In this problem we’re going to build the part of
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   our javascript parser that handles javascript
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   expressions. This is pretty straightforward, just
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   like the last problem where we’re essentially
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   numerating all the rules that we’ve predefined
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   for our javascript language. So let’s go right
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   through the I, the E.
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    So here we have the supply code for the
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    problem and if we look closely, we see that
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    almost all the parse float are numerated to
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    exactly what they should be. We have Identifier,
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    numbers, strings, true and false, how to handle a
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    not keyword do the opposite and then for
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    expressions. We are also given an enumeration
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    of the precedence and the associativity for each
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    of these operations.
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    So really we have everything we need in the
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    problem description to do this problem. And as
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    you can see here, I’ve already filled in the
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    precedence ordering for the operations. And this
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    has simply taken almost exactly right from the
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    comment given in the problem where or is listed
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    at the lowest precedence and we go all the way
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    up to division, right here. I’ve also added not
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    just to make it work.
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    So let’s start filling in the rules. My first rule is
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    going to handle. If we add a matching left and
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    right parenthesis, the expression that is equal to
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    is simply the contents of the parenthesis, pretty
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    straightforward. And now I have four rules for
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    some of our literal values. We have a number,
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    we’re going to say number and then the contents
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    of that string, just simply say the word string,
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    we’ve matched true or false, we’re going to
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    return the specified tuples. If we see a notch,
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    then we simply have in our Pastry that we’re not
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    and then the contents that are being.
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    Afterwards, we have about a dozen or so binary
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    rules. Addition, subtraction, times, modulus
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    division etcetera, etcetera and to save some time
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    I could enumerate each function, but I want to
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    take a short cut. So here I’ve said if we match
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    any of these things, I’m calling it a binary
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    operation. For the first element is new left,
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    upper end of the binary operation. The next
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    entry in our tuple is going to be the operation
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    being used and the last one its going to be the
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    right upper hand of the binary operation.
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    And now I have the expressions for function
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    calls, not just decorations, which we had in the
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    last problem. A function call is going to be
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    identifier, with optional argument in between
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    parenthesis. And the code for handling optional
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    arguments is almost exactly the same as the
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    code we use to handle, optional arguments in
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    the function decoration. In fact, I think it is
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    exactly the same. And with all that, we’ve done
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    it. It’s about 50 lines a code and we are happy.