sexp-template/src/resolver.js

const AST = require("./ast");

module.exports = class Resolver {
  constructor() {
    this.tree = [];
    this.context = {};

    this.stdlib = {
      if: (predicate, left, right) => {
        const resolvedPredicate = this.resolveNode(predicate);

        this.typecheck(resolvedPredicate, AST.Boolean);

        if (resolvedPredicate && resolvedPredicate.value === true) {
          return this.resolveNode(left);
        } else if (resolvedPredicate && resolvedPredicate.value === false) {
          return this.resolveNode(right);
        }
      },
      list: args => {
        let elements = [];

        args.forEach(arg => {
          elements.push(this.resolveNode(arg));
        });

        return new AST.List({
          elements: elements
        });
      },
      quote: value => {
        return new AST.Symbol({ value: value });
      },
      htmlElement: node => {
        let resolvedArgs = [];

        node.args.forEach(arg => {
          resolvedArgs.push(this.resolveNode(arg));
        });

        return new AST.Application({
          functionName: node.functionName,
          args: resolvedArgs
        });
      },
      "=": (left, right) => {
        this.typecheck(right, left.constructor);

        if (left.constructor.name === "List") {
          if (left.elements.length !== right.elements.length) {
            return new AST.Boolean({ value: false });
          }

          let equal = true;

          left.elements.forEach((el, i) => {
            this.typecheck(el.value, right.elements[i].constructor);
            if (el.value !== right.elements[i].value) {
              equal = false;
            }
          });

          return new AST.Boolean({ value: equal });
        }

        return new AST.Boolean({ value: left.value === right.value });
      },
      ">": (left, right) => {
        this.typecheck(left, AST.Number) && this.typecheck(right, AST.Number);
        return new AST.Boolean({ value: left.value > right.value });
      },
      "<": (left, right) => {
        this.typecheck(left, AST.Number) && this.typecheck(right, AST.Number);
        return new AST.Boolean({ value: left.value < right.value });
      },
      ">=": (left, right) => {
        this.typecheck(left, AST.Number) && this.typecheck(right, AST.Number);
        return new AST.Boolean({ value: left.value >= right.value });
      },
      "<=": (left, right) => {
        this.typecheck(left, AST.Number) && this.typecheck(right, AST.Number);
        return new AST.Boolean({ value: left.value <= right.value });
      },
      and: args => {
        let and = true;

        args.forEach(arg => {
          this.typecheck(arg, AST.Boolean);
          if (arg.value === false) {
            and = false;
          }
        });

        return new AST.Boolean({ value: and });
      },
      or: args => {
        let or = false;

        args.forEach(arg => {
          this.typecheck(arg, AST.Boolean);
          if (arg.value === true) {
            or = true;
          }
        });

        return new AST.Boolean({ value: or });
      },
      lambda: function(parameter, body) {
        console.log(parameter, body);
      }
    };
  }

  resolve(tree, context) {
    this.context = context;

    tree.forEach(node => {
      this.tree.push(this.resolveNode(node));
    });

    return this.tree;
  }

  resolveNode(node, context) {
    if (!context) {
      context = this.context;
    }

    switch (node.constructor.name) {
      case "Boolean":
      case "Number":
      case "String":
        return node;
      case "Attribute":
        return new AST.Attribute({
          name: node.name,
          value: this.resolveNode(node.value)
        });
      case "Identifier":
        return this.lookup(node.name);
      case "Application":
        if (this.stdlib.hasOwnProperty(node.functionName.name)) {
          const f = this.stdlib[node.functionName.name];

          if (["list", "and", "or"].includes(node.functionName.name)) {
            return f(node.args);
          }

          let resolvedArgs = [];

          if (node.functionName.name === "quote") {
            resolvedArgs = node.args;
          } else {
            node.args.forEach(arg => {
              resolvedArgs.push(this.resolveNode(arg));
            });
          }

          return f(...resolvedArgs);
        }

        return this.stdlib.htmlElement(node);
    }
  }

  lookup(name) {
    console.log(name);
    const result = this.context[name];
    return this.wrap(result);
  }

  wrap(value) {
    switch (value.constructor.name) {
      case "String":
        return new AST.String({ value: value });
      case "Number":
        return new AST.Number({ value: value });
      case "Array":
        return new AST.List({ elements: value.map(this.wrap) });
    }
  }

  typecheck(value, type) {
    console.log(value);
    console.log(type);
    if (value.constructor.name !== type.name) {
      throw `Type error: expected a ${type.name} but got a ${
        value.constructor.name
      }`;
    }
  }
};