Guide to Programming Languages
Well, we just saw the code for processing these tokens, and we know that it went to a bit of trouble to store the beginning position, lexps, and then the ending position, but then–phwoomp–subtract out 9. So this is way too much. We went to a lot of trouble to drop
Now that we’ve seen this one way, let’s see this from a different perspective. [Brendan Eich, CTO, Mozilla] [Wes Weimer, Professor, University of Virginia] Let me ask you a question that’s actually of personal interest and curiosity to me. I’m teaching in this class a number of elements of functional programming, list comprehensions in Python,…
So once again, it’s time to summarize what we’ve learned in this unit. Just as English sentences could be broken up into words, so can HTML and JavaScript be broken up into tokens, typically separated by spaces. Some of the more complicated token types we looked at were number, word, and string. Since these correspond…
Now let’s work through it from the top. Initially x is 1, and then I define a new function tricky, but I haven’t called it yet, so I’m not actually going to make any new variable spaces over here. And then I print out the value of x. Currently x is 1, and now I…
Well, x equals three is certainly a statement. We’ve seen examples like this before. You might have thought that a statement has to end in a semicolon, but if we scroll back to our grammar a bit, we see, no, a statement can be identifier equals expression, and those semicolons come in when we have…
That’s not the only new power we’re going to introduce. Suppose that you wanted to square all of the numbers in the list 1, 2, 3, 4, 5. Here’s one way to do it. The function map takes a function as its first argument and then a list, and it applies that function to each…
That was not a proof, but it just so happens that grammars are strictly greater, have more expressive power than regular expressions. Anything we could specify with a regular expression, we can also specify with a grammar. Let’s try it out. Here’s another regular expression: p plus followed by i question mark. I’m going to…
Let’s explore a bit more in this brave new world of finite state machines. Over here, I’ve drawn a different finite state machine, again with 3 states. I’m going to draw some possible strings down here, and I want you to check each one that would be accepted by this finite state machine. So in…
Let’s go through the answer together. We definitely want to name our procedure t_string, and now the real trick to this is just writing a good regular expression. Here I’ve written a regular expression that starts with a double quote, ends with a double quote, and can have anything that’s not a double quote– remember…
Well, let’s go through 1 possible answer together. We’re assigning to the variable, regexp, a regular expression. Those start with r and then double quotes. The first thing I want to do is match the function name. That will be [a – z]+. Now I want to match immediately an opening parenthesis. I will escape…