75 lines
2 KiB
TypeScript
75 lines
2 KiB
TypeScript
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var fs = require('fs');
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type Some<T> = { _tag: "Some"; value: T };
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type None = {_tag: "None"};
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/**
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* @description Like the `Some(a)` and `None` in Rust.
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*
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* @example
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* ```ts
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* let exam1 : Maybe<Number> = { _tag: "Some", value: 12 };
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* let exam2 : Maybe<Number> = None;
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* ```
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*/
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export type Maybe<T> = Some<T> | None;
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/**
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* @description
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* the pair of the string to be matched later and the string that have been matched
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* @param matched : string have been matched
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* @param remained : string will be tested whether it'll be matched.
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*/
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export type MatcheePair = {matched : string; remained : string};
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/**
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* @description
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* it returns a function which test if the first char of the `remained` part of
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* the argument of the function is `c`, if it's true, update the `MatchedPair` wrapped
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* in `Some`. Otherwise, it returns `None`.
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* * @param c : the char to be test.
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* @returns the updated `MatchedPair` wrapped in `Some(x)` or `None`.
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*/
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export function match1Char(c : string) : (m: MatcheePair) => Maybe<MatcheePair> {
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return (m : MatcheePair)=>{
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const charToBeMatched = m.remained[0];
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if (charToBeMatched === c){
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return {_tag: "Some", value :{
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matched : m.matched + charToBeMatched,
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remained : m.remained.substring(1)}};
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}
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else{
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return {_tag: "None"};
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}
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}
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};
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/**
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* convert the one-char string to codepoint.
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* @param s : the string to code point.
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* @returns if `s.length > 1` return error; otherwise, return the codepoint of `s`.
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*/
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export function charToCodepoint(s : string): number{
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if (s.length > 1){
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throw new Error("Error: the length of input string for "+s+ "is "+s.length+`,
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however, it should be 1.`);
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}else{
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return s.charCodeAt(0);
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}
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}
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/**
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* @description thendo(input, f, ...) like
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* a ==> f
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*/
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export function thenDo<T>(input : Maybe<T>, f : Function) : Maybe<T>{
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if (input._tag == "None"){
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return input;
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}
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else{
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let inner = input.value;
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return f(inner);
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}
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}
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