77 lines
1.4 KiB
Markdown
77 lines
1.4 KiB
Markdown
## 3.1. The alternative
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### The if structure
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```Ocaml
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if cond then expr1 else expr2
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```
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> ⚠️ `expr1` and `expr2` have to be the same type. `cond` is a `bool`
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**For exemple**
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```Ocaml
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# if 1<2 then "higher" else "lower" ;;
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-: string = "higher"
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```
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**Exercise : absolute program**
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```Ocaml
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# let abs(x) =
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if x>0 then x
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else -x ;;;
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val abs : int -> int <fun>
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```
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## 3.2. Exceptions
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### Division by 0:
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```Ocaml
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# 1/0
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Exception : Division by zero
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```
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### Failwith:
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Failwith is a function that take a string argument (the reason) and return the error. That way, we can raise an error into our code
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```Ocaml
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# failwith;;
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-: string -> a = <fun>
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# failwith "oops";;
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Exception : Failwith "oops"
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```
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### invalid_arg:
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Invalid_arg is a function that take a string argument (the reason) and return the error. That way, we can raison an error about an argument
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```Ocaml
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# invalid_arg "oops";
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Exception: Invalid_argument "oops"
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(*example*)
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# let div a b =
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if b = 0 then invalid_arg("div: b = 0")
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else a/b ;;;
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val div int -> int -> int = <fun>
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```
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## 3.3. Filtering
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### Explicit filtering
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> Explicit means that you matches the value
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**General syntax**
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```Ocaml
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match expr with pattern1 -> result1 | pattern2 -> result2 | ... | patternn -> resultn
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```
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> All expressions and pattern must avec the same type
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**Example**
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```Ocaml
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# let f x = match x with
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0 -> 18
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1 -> 24
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y -> y + y;;
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val f : int -> int = <fun>
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# f 1;;
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- : int = 24
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