blogng/blog/2015-08-22-recursion.markdown

---
comments: true
date: 2015-08-22 00:28
layout: post
tags: haskell, recursion, fibonacci numbers
title: Recursion
---

```haskell
fibonacci :: [Integer]
fibonacci = 1:1:(zipWith (+) fibonacci (tail fibonacci))
```

Above is a simple function that generates an infinite stream of fibonacci numbers. Its written in haskell.

This is a piece of code that made me think a lot lately, it make clever use of recursion to define the stream and computes with a linear number of additions. I think its pretty damn sexy!

## Notes:
- Many thanks to a co-worker who helped me figure this out.
- I hear that there are more efficient ways to compute fibonacci numbers (namley O(logn)). - should investigate this
intial commit 2017-01-22 21:30:42 +00:00			`---`
			`comments: true`
Convert from old categories to tags import sys import yaml with open(sys.argv[1]) as fp: data = fp.read() if not data.find("---") == 0: # no head print("NO YAML HEAD FOUND") sys.exit(-1) data = data[3:] head_end = data.find("---") head = data[0:head_end] data = data[head_end+3:] metadata = yaml.safe_load(head) cats = metadata.pop('categories', None) if cats != None: if type(cats) == list: tags = cats elif type(cats) == str: tags = cats.split() tags = list(map(lambda t: t.lower(), tags)) metadata["tags"] = ", ".join(tags) new_data = f"---\n{yaml.dump(metadata, default_flow_style=False)}---{data}" # write it print(f"coverted: categories to tags: {tags} - {sys.argv[1]}") with open(sys.argv[1], "w") as fp: fp.write(new_data) sys.exit(0) if not metadata.get("tags", None): metadata["tags"] = "untagged" new_data = f"---\n{yaml.dump(metadata, default_flow_style=False)}---{data}" print(f"untagged: {sys.argv[1]}") # write it with open(sys.argv[1], "w") as fp: fp.write(new_data) sys.exit(0) print("No changes needed") 2019-01-28 22:16:27 +00:00			`date: 2015-08-22 00:28`
			`layout: post`
			`tags: haskell, recursion, fibonacci numbers`
			`title: Recursion`
intial commit 2017-01-22 21:30:42 +00:00			`---`

			```haskell
			`fibonacci :: [Integer]`
			`fibonacci = 1:1:(zipWith (+) fibonacci (tail fibonacci))`
			```

			`Above is a simple function that generates an infinite stream of fibonacci numbers. Its written in haskell.`

			`This is a piece of code that made me think a lot lately, it make clever use of recursion to define the stream and computes with a linear number of additions. I think its pretty damn sexy!`

			`## Notes:`
			`- Many thanks to a co-worker who helped me figure this out.`
			`- I hear that there are more efficient ways to compute fibonacci numbers (namley O(logn)). - should investigate this`