Ocaml Review

Getting My Feet Wet in Ocaml

let a = 5;;

;; terminates ocaml phrases.
let is not an assignment. It identifies new identifier with new scope.
let rec defines a recursive function.

Data Types
int, float, bool, char, string

Pattern Matching

let rec doNothing list = match list with
[] -> []
| head::tail -> head::doNothing(tail);;

the | defines different cases to match with.
[] case implies that list is a list and this is the case if it's empty.
head::tail  case also implies that list is a list and head is the first element of the list and tail is the sublist without that head.

Ocaml can't modify in-place a list after it's built they are immutable data structures.
A function with a list as input will build and return a new list with or without the elements of the input list.

Typing

let deriv f dx = function x -> ( f (x +. dx) -. f x ) /. dx;;

This phrase evaluates to

(float -> float) -> float -> float -> float = <fun>
1                         2          3          4         5

1. (float -> float) is the type of f

The braces mean that f is a function. It takes in a float and outputs a float

since in f (x +. dx) we are passing in a floating point number to f because +. is a floating point addition.

And ( f (x +. dx) -. f x ) indicates that f outputs a floating point number because -. is floating point subtraction.

2. float is what dx type is.

3. float is what x's type is.

4. float is what the function deriv's output type is.

5. <fun> indicates that it's a function.

User Defined Types
type ratio = {num: int; denom: int};;

Here is a user defined type to represent a fraction.

let add_ratio r1, r2 = {
num = r1.num * r2.denom + r2.num * r1.denom;
denom = r1.denom * r2.denom};;

ratio -> ratio -> ratio

Here we can return a ratio using the curly braces and setting the num and denom, separated by a ;.

We can also access the denom and num of r1 and r2 using the . operator.

Variant Type
Lists the possible shapes for values of that type.

type sign = Positive | Negative;;

Good for trees, pattern matching.

Imperative Programming Features

for ... to ... do
 ...
done;

while ... do
 ....
done;

Arrays
Two ways of creation

1. Array.create

let arr = Array.create len 0.0;;

len = length
0.0 = initial values of the array

2. [| |]

let arr = [|1;2;3;|];;

References

ref j

defines j as a reference

j := !j;;

:= assigns to the contents of j.

! accesses the contents of j.