ohm-js/src/Builder.js

An object-oriented language for parsing and pattern matching

import {Grammar} from './Grammar.js';
import {GrammarDecl} from './GrammarDecl.js';
import * as pexprs from './pexprs.js';

// --------------------------------------------------------------------
// Private stuff
// --------------------------------------------------------------------

export class Builder {
  constructor() {
    this.currentDecl = null;
    this.currentRuleName = null;
  }

  newGrammar(name) {
    return new GrammarDecl(name);
  }

  grammar(metaInfo, name, superGrammar, defaultStartRule, rules) {
    const gDecl = new GrammarDecl(name);
    if (superGrammar) {
      // `superGrammar` may be a recipe (i.e. an Array), or an actual grammar instance.
      gDecl.withSuperGrammar(
        superGrammar instanceof Grammar ? superGrammar : this.fromRecipe(superGrammar),
      );
    }
    if (defaultStartRule) {
      gDecl.withDefaultStartRule(defaultStartRule);
    }
    if (metaInfo && metaInfo.source) {
      gDecl.withSource(metaInfo.source);
    }

    this.currentDecl = gDecl;
    Object.keys(rules).forEach(ruleName => {
      this.currentRuleName = ruleName;
      const ruleRecipe = rules[ruleName];

      const action = ruleRecipe[0]; // define/extend/override
      const metaInfo = ruleRecipe[1];
      const description = ruleRecipe[2];
      const formals = ruleRecipe[3];
      const body = this.fromRecipe(ruleRecipe[4]);

      let source;
      if (gDecl.source && metaInfo && metaInfo.sourceInterval) {
        source = gDecl.source.subInterval(
            metaInfo.sourceInterval[0],
            metaInfo.sourceInterval[1] - metaInfo.sourceInterval[0],
        );
      }
      gDecl[action](ruleName, formals, body, description, source);
    });
    this.currentRuleName = this.currentDecl = null;
    return gDecl.build();
  }

  terminal(x) {
    return new pexprs.Terminal(x);
  }

  range(from, to) {
    return new pexprs.Range(from, to);
  }

  param(index) {
    return new pexprs.Param(index);
  }

  alt(...termArgs) {
    let terms = [];
    for (let arg of termArgs) {
      if (!(arg instanceof pexprs.PExpr)) {
        arg = this.fromRecipe(arg);
      }
      if (arg instanceof pexprs.Alt) {
        terms = terms.concat(arg.terms);
      } else {
        terms.push(arg);
      }
    }
    return terms.length === 1 ? terms[0] : new pexprs.Alt(terms);
  }

  seq(...factorArgs) {
    let factors = [];
    for (let arg of factorArgs) {
      if (!(arg instanceof pexprs.PExpr)) {
        arg = this.fromRecipe(arg);
      }
      if (arg instanceof pexprs.Seq) {
        factors = factors.concat(arg.factors);
      } else {
        factors.push(arg);
      }
    }
    return factors.length === 1 ? factors[0] : new pexprs.Seq(factors);
  }

  star(expr) {
    if (!(expr instanceof pexprs.PExpr)) {
      expr = this.fromRecipe(expr);
    }
    return new pexprs.Star(expr);
  }

  plus(expr) {
    if (!(expr instanceof pexprs.PExpr)) {
      expr = this.fromRecipe(expr);
    }
    return new pexprs.Plus(expr);
  }

  opt(expr) {
    if (!(expr instanceof pexprs.PExpr)) {
      expr = this.fromRecipe(expr);
    }
    return new pexprs.Opt(expr);
  }

  not(expr) {
    if (!(expr instanceof pexprs.PExpr)) {
      expr = this.fromRecipe(expr);
    }
    return new pexprs.Not(expr);
  }

  lookahead(expr) {
    if (!(expr instanceof pexprs.PExpr)) {
      expr = this.fromRecipe(expr);
    }
    return new pexprs.Lookahead(expr);
  }

  lex(expr) {
    if (!(expr instanceof pexprs.PExpr)) {
      expr = this.fromRecipe(expr);
    }
    return new pexprs.Lex(expr);
  }

  app(ruleName, optParams) {
    if (optParams && optParams.length > 0) {
      optParams = optParams.map(function(param) {
        return param instanceof pexprs.PExpr ? param : this.fromRecipe(param);
      }, this);
    }
    return new pexprs.Apply(ruleName, optParams);
  }

  // Note that unlike other methods in this class, this method cannot be used as a
  // convenience constructor. It only works with recipes, because it relies on
  // `this.currentDecl` and `this.currentRuleName` being set.
  splice(beforeTerms, afterTerms) {
    return new pexprs.Splice(
        this.currentDecl.superGrammar,
        this.currentRuleName,
        beforeTerms.map(term => this.fromRecipe(term)),
        afterTerms.map(term => this.fromRecipe(term)),
    );
  }

  fromRecipe(recipe) {
    // the meta-info of 'grammar' is processed in Builder.grammar
    const args = recipe[0] === 'grammar' ? recipe.slice(1) : recipe.slice(2);
    const result = this[recipe[0]](...args);

    const metaInfo = recipe[1];
    if (metaInfo) {
      if (metaInfo.sourceInterval && this.currentDecl) {
        result.withSource(this.currentDecl.sourceInterval(...metaInfo.sourceInterval));
      }
    }
    return result;
  }
}