62 lines
2 KiB
JavaScript
62 lines
2 KiB
JavaScript
// This module ensures that we never accidentally create a Symbol for the same type twice.
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// Maybe we shouldn't use Symbols for types, but we also cannot use primitive values for types because they may accidentally overlap with 'real' values (that are not types)
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// We also cannot use objects for types because similar to Symbols, objects are only equal to themselves if we use them as Map keys.
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import { DefaultMap } from "./util.js";
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// Global store of function types:
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const fnTypes = new DefaultMap(() => new Map());
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export const fnType = ({in: inType, out: outType}) => {
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const m2 = fnTypes.getdefault(inType, true);
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if (m2.has(outType)) {
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return m2.get(outType);
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}
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else {
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const fnType = {in: inType, out: outType};
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m2.set(outType, fnType);
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return fnType;
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}
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};
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// Global store of list types:
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const listTypes = new Map();
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export function getListType(elementType) {
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if (listTypes.has(elementType)) {
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// only generate each list type once
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// this would not be necessary if we could define our own equality and hash functions on objects in JavaScript.
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return listTypes.get(elementType);
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}
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else {
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const type = Symbol('ListOf:' + elementType.toString());
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listTypes.set(elementType, type);
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return type;
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}
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}
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// Global store of product types:
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const productTypes = new DefaultMap(() => new Map());
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export const prodType = (leftType, rightType) => {
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const m2 = productTypes.getdefault(leftType, true);
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if (m2.has(rightType)) {
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return m2.get(rightType);
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}
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else {
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const pt = Symbol(`${leftType.toString()} × ${rightType.toString()}`);
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m2.set(rightType, pt);
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return pt;
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}
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}
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// Global store of sum types:
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const sumTypes = new DefaultMap(() => new Map());
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export const sumType = (leftType, rightType) => {
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const m2 = sumTypes.getdefault(leftType, true);
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if (m2.has(rightType)) {
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return m2.get(rightType);
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}
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else {
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const st = Symbol(`${leftType.toString()} + ${rightType.toString()}`);
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m2.set(rightType, st);
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return st;
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}
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}
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