mframejs/src/mframejs/binding/ast/ast.ts

simple framework

import { SymbolContainer } from './symbolContainer';
import { SymbolTemplate } from './symbolTemplate';
import { ITokens } from '../../interface/exported';


/**
 * Using Douglas Crockford paper on Vaughan Pratt "Top Down Operator Precedence"
 * For more info about this look here
 * https://crockford.com/javascript/tdop/tdop.html (added to docs folder so I dont loose it)
 * Not everything is used
 *
 * This class will do most of the heavy lifting of generating the AST for our expressions
 * It will need symbols added and a symbol container
 *
 */
export class AST {

    public behavior: any;
    public valueConverter: any;
    private tokens: ITokens[];
    public currentStatement: any = null;
    public currentTokenIndex = 0;
    public currentToken: any;
    private symbolContainer: SymbolContainer;
    public statementsArray: any[];


    /**
     * start the parsing of tokens
     *
     */
    public start(tokens: ITokens[]) {
        // set tokens
        this.tokens = tokens;

        // clear
        this.currentStatement = null;
        this.currentTokenIndex = 0;
        this.currentToken = null;

        // get first token
        this.advance();

        // generate ast
        const ast = this.statements();

        // return ast
        return ast;
    }



    /**
     * adds symbol container we will use to get/set our symbols
     *
     */
    public addSymbolContainer(symbolContainer: SymbolContainer) {
        this.symbolContainer = symbolContainer;
    }



    /**
     * Symbol id and an optional binding power that defaults to 0 and returns a symbol object for that id.
     * If the symbol already exists in the symbol_table, the function returns that symbol object.
     * Otherwise, it makes a new symbol object that inherits from the symbolTemplate, stores it in the symbol container, and returns it.
     * A symbol object initially contains an id, a value, a left binding power, and the stuff it inherits from the symbolTemplate.
     *
     */
    public symbol(id: string, bp?: number) {
        let s = this.symbolContainer[id];
        bp = bp || 0;
        if (s) {
            if (bp >= s.lbp) {
                s.lbp = bp;
            }
        } else {
            s = new SymbolTemplate();
            s.id = s.value = id;
            s.lbp = bp;
            this.symbolContainer[id] = s;
        }

        return s;
    }



    /**
     * Prefix operators are right associative.
     * A prefix does not have a left binding power because it does not bind to the left.
     * Prefix operators can also sometimes be reserved words.
     *
     */
    public prefix(id: string, nud?: Function) {
        const s = this.symbol(id);
        const astInstance = this;
        s.nud = nud || function () {
            // scope.reserve(this);
            this.first = astInstance.expression(70);
            this.arity = 'unary';

            return this;
        };

        return s;
    }



    /**
     * The infix function takes an id, a binding power, and an optional led function.
     * If a led function is not provided, the infix function supplies a default led that is useful in most cases.
     *
     */
    public infix(id: string, bp?: number, led?: Function) {
        const s = this.symbol(id, bp);
        const astInstance = this;
        s.led = led || function (left: any) {
            this.first = left;
            this.second = astInstance.expression(bp);
            this.arity = 'binary';

            return this;
        };

        return s;
    }



    /**
     * Those infix operators are left associative.
     * We can also make right associative operators, such as short-circuiting logical operators, by reducing the right binding power.
     *
     */
    public infixr(id: string, bp: number, led?: Function) {
        const s = this.symbol(id, bp);
        const astInstance = this;
        s.led = led || function (left: any) {
            this.first = left;
            this.second = astInstance.expression(bp - 1);
            this.arity = 'binary';

            return this;
        };

        return s;
    }



    /**
     * The stmt function is used to add statement symbols to the symbol table. It takes a statement id and an std function.
     *
     */
    public stmt(id: string, f: Function) {
        const x = this.symbol(id);
        x.std = f;

        return x;
    }



    /**
     * We could use infixr to define our assignment operators,
     * but we will make a specialized assignment function because we want it to do two extra bits of business:
     * examine the left operand to make sure that it is a proper lvalue,
     * and set an assignment member so that we can later quickly identify assignment statements.
     */
    public assignment = function (id: string) {
        const astInstance = this;

        return this.infixr(id, 10, function (left: any) {
            if (left.id !== '.' && left.id !== '[' &&
                left.arity !== 'variable') {
                left.error('Bad lvalue.');
            }
            this.first = left;
            this.second = astInstance.expression(9);
            this.assignment = true;
            this.arity = 'binary';

            return this;
        });
    };



    /**
     * The statement function parses one statement.
     * If the current token has an std method, the token is reserved and the std is invoked.
     * Otherwise,we assume an expression statement terminated with a semi-colon.
     * For reliability, we will reject an expression statement that is not an assignment or invocation.
     *
     */
    public statement() {
        const n = this.currentToken;
        let v;
        if (n.std) {
            this.advance();
            // scope.reserve(n);

            return n.std();
        }
        v = this.expression(0);

        return v;
    }



    /**
     * The statements function parses statements until it sees (end) or } which signals the end of a block.
     * The function returns a statement, an array of statements, or null if there were no statements present.
     *
     */
    public statements() {
        this.statementsArray = [];
        let s;
        while (true) {
            if (this.currentToken.id === '}' || this.currentToken.id === '(end)') {
                break;
            }
            s = this.statement();
            if (s) {
                this.statementsArray.push(s);
            }
        }

        return this.statementsArray.length === 0 ? null : this.statementsArray.length === 1 ? this.statementsArray[0] : this.statementsArray;
    }



    /**
     * The advance function makes a new token object from the next simple token in the array and assigns it to the token variable.
     * It can take an optional id parameter which it can check against the id of the previous token.
     * The new token object's prototype is a (name) token in the current scope or a symbol from the symbol table.
     * The new token's arity is "name", "literal", or "operator".
     * Its arity may be changed later to "binary", "unary", or "statement" when we know more about the token's role in the program.
     *
     */
    public advance(expected?: string) {

        let type, o, token, value;
        token = this.tokens[this.currentTokenIndex];

        if (token && expected) {
            const nextToken = this.tokens[this.currentTokenIndex + 1];
            if (expected === '}' && nextToken && (nextToken.value === '|' || nextToken.value === '&')) {
                return;
            }

            // -> will happend if signle inside expression ${values  | valuconverter}
            const prevToken = this.tokens[this.currentTokenIndex - 1];
            if (expected === '}' && prevToken && (prevToken.value === '|' || prevToken.value === '&')) {
                return;
            }
        }


        if (this.currentTokenIndex >= this.tokens.length) {
            this.currentToken = this.symbolContainer['(end)'];

            return;
        }

        this.currentTokenIndex += 1;
        value = token.value;
        type = token.type;

        if (type === 'variable') {

            type = 'variable';
            o = this.symbolContainer['(variable)'];


        } else if (type === 'operator') {

            o = this.symbolContainer[value];
            if (!o) {
                console.warn('Unknown operator.', token);
            }

        } else if (type === 'string' || type === 'number') {

            type = 'literal';
            o = this.symbolContainer['(literal)'];

        } else {

            console.warn('Unexpected token.', token);

        }

        this.currentToken = Object.create(o);
        this.currentToken.value = value;
        this.currentToken.arity = type;
        if ((<any>token).root) {
            this.currentToken.root = true;
        }

        return this.currentToken;
    }



    /**
     * The heart of Pratt's technique is the expression function.
     * It takes a right binding power that controls how aggressively it binds to tokens on its right.
     *
     */
    public expression(rbp: any) {
        let left;
        let token = this.currentToken;
        this.advance();
        left = token.nud();
        try {
            while (rbp < this.currentToken.lbp) {
                token = this.currentToken;
                this.advance();
                left = token.led(left);
            }
        } catch (e) {
            console.warn('parser fail');

        }

        return left;
    }


}