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December 26, 2020 19:07
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This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -0,0 +1,118 @@ // Common Utilities function compose(...fns) { const apply = (arg, fn) => fn(arg); return (initial) => fns.reduceRight(apply, initial); } function curry(arity, fn, ...rest) { if(arity <= rest.length) { return fn(...rest); } return curry.bind(null, arity, fn, ...rest); } // Transducers stuff const Combine = { push: (state, value) => (state.push(value), state), add: (state, value) => state.add(value), concat: (state, value) => state.concat(value) }; function reduce(reducer, initial, collection) { let state = initial; for(let value of collection) { state = reducer(state, value); } return state; } function transduce(combine, initial, transducer, collection) { return reduce(transducer(combine), initial, collection); } const Into = { array: curry(2, function(transducer, collection) { return transduce(Combine.push, [], transducer, collection); }), string: curry(2, function(transducer, collection) { return transduce(Combine.concat, "", transducer, collection) }), set: curry(2, function(transducer, collection) { return transduce(Combine.add, new Set(), transducer, collection); }), }; function filter(predicate, next) { if(arguments.length === 1) { return (_next) => filter(predicate, _next); } return function reducer(state, value) { if(predicate(value)) { return next(state, value); } return state; }; } function map(transform, next) { if(arguments.length === 1) { return (_next) => map(transform, _next); } return function reducer(state, value) { return next(state, transform(value)); }; } // Contrived example const is_even = number => number % 2 === 0; const is_positive = number => number > 0; const add_message = number => `The number is: ${number}`; const transducer = compose( filter(is_positive), filter(is_even), map(add_message) ); const array = [-2, -1, 0, 1, 2, 3]; const set = new Set([-2, -1, 0, 1, 2, 3]); const to_string = Into.string(transducer); console.log( '\nTransducer with Array.reduce\n', array.reduce(transducer(Combine.push), []), '\n' ); console.log( 'Transducer with custom reduce (on Array)\n', Into.array(transducer, array), '\n' ); console.log( 'Transducer with custom reduce (on Set)\n', Into.set(transducer, set), '\n' ); console.log( 'Transducer with custom reduce (from Array to String)\n', Into.string(transducer, array), '\n' ); console.log( 'Transducer with custom reduce (from Set to String)\n', to_string(set), );