git.kianting.info Git - uann/blob - src/index.ts

   1 var fs = require('fs');
   2
   3 type Some<T> = { _tag: "Some"; value: T };
   4 type None = {_tag: "None"};
   5
   6 /**
   7  * @description Like the `Some(a)` and `None` in Rust.
   8  *
   9  * @example
  10  * ```ts
  11  * let exam1 : Maybe<Number> = { _tag: "Some", value: 12 };
  12  * let exam2 : Maybe<Number> = None;
  13  * ```
  14  */
  15 export type Maybe<T> = Some<T> | None;
  16
  17
  18 /**
  19  * @description
  20  * the pair of the string to be matched later and the string that have been matched
  21  * @param matched : string have been matched
  22  * @param remained : string will be tested whether it'll be matched.
  23  */
  24 export type MatcheePair = {matched : string; remained : string};
  25
  26 /**
  27  * @description
  28  * it returns a function which test if the first char of the `remained` part of
  29  *  the argument of the function is `c`, if it's true, update the `MatchedPair` wrapped
  30  * in `Some`. Otherwise, it returns `None`.
  31  *  * @param c : the char to be test.
  32  * @returns the updated `MatchedPair` wrapped in `Some(x)` or `None`.
  33  */
  34 export function match1Char(c : string) : (m: MatcheePair) => Maybe<MatcheePair> {
  35     return (m : MatcheePair)=>{
  36         const charToBeMatched = m.remained[0];
  37         if (charToBeMatched === c){
  38             return {_tag: "Some", value :{
  39                     matched : m.matched + charToBeMatched,
  40                     remained : m.remained.substring(1)}};
  41         }
  42         else{
  43             return {_tag: "None"};
  44         }
  45     }
  46 };
  47
  48 /**
  49  * convert the one-char string to codepoint.
  50  * @param s : the string to code point.
  51  * @returns if `s.length > 1` return error; otherwise, return the codepoint of `s`.
  52  */
  53 export function charToCodepoint(s : string): number{
  54     if (s.length > 1){
  55         throw new Error("Error: the length of input string for "+s+ "is "+s.length+`,
  56         however, it should be 1.`);
  57     }else{
  58         return s.charCodeAt(0);
  59     }
  60 }
  61
  62 /**
  63  *  @description thendo(input, f, ...) like
  64  * a ==> f
  65  */
  66 export function thenDo<T>(input : Maybe<T>, f : Function) : Maybe<T>{
  67     if (input._tag == "None"){
  68         return input;
  69     }
  70     else{
  71         let inner = input.value;
  72         return f(inner);
  73     }
  74 }