Two posts in two days? Madness!
Posts in StackLang:
But really, it got a bit late yesterday so I figured I’d split this into two different posts.
Two posts in two days? Madness!
But really, it got a bit late yesterday so I figured I’d split this into two different posts.
Let’s continue StackLang Part VII: New CLI and Datatypes and implement lists stacks in the compiler!
In this post:
We’ve gone through all sorts of things building up the StackLang language so far:
But what can we actually do with it?
It’s been a bit, but I hope it’s worth it. StackLang, part 5: compiling to C!
StackLang, part 4: an interpreter. Here we go again!
This time, the goal is to actually get code running
StackLang, part 3: parsing. This is going to be the most complicated one thus far! Onward.
StackLang, part 2: lexing.
It’s quite often the simplest part of implementing a programming language (although parsers for s-expression based languages come close), but it’s still something that needs done. So here we go!
I enjoy writing programming languages. Example: Tiny. Let’s do that again.
This time, StackLang:
{
@[n fact]
1
{ n 1 - $fact fact n * }
N 1 <= if
} @fact
5 $fact fact writeln
Bit of gibberish there, I suppose, but the goal is to write everything in a postfix/stack based model. So n 1 - $fact fact n * is equivalent to fact(fact, n - 1) * n in a more traditional language.
Over the next few posts, I hope to write up where I am thus far and what’s next.
Part 1: Implement a Turing machine defined as such:
Begin in state A. Perform a diagnostic checksum after 6 steps.
In state A: If the current value is 0: - Write the value 1. - Move one slot to the right. - Continue with state B. If the current value is 1: - Write the value 0. - Move one slot to the left. - Continue with state B.
…
> What is the final number of `1s` on the tape?
Most of this problem actually came down to reading the input:
```python
# Map of (current state, current value, key) -> value
# key is one of value, offset, state
transitions = {}
breakpoint = 0
state = None
pointer = 0
one_bits = set()
for line in lib.input():
line = line.strip('- ')
arg = line.split()[-1][:-1]
if arg == 'steps':
arg = line.split()[-2]
try:
arg = int(arg)
except:
pass
# Store values based on that argument
if line.startswith('Begin'):
state = arg
elif line.startswith('Perform'):
breakpoint = arg
elif line.startswith('In'):
current_state = arg
elif line.startswith('If'):
current_value = arg
elif line.startswith('Write'):
transitions[current_state, current_value, 'value'] = arg == 1
elif line.startswith('Move'):
transitions[current_state, current_value, 'offset'] = 1 if arg == 'right' else -1
elif line.startswith('Continue'):
transitions[current_state, current_value, 'state'] = arg
As we did in part 1 of day 22, we’ll use a set to store the current state (store 1, if an index is not in the set, it’s 0). That gives us the ability to grow unbounded (so long as we have enough RAM).