fast_expressions

Fast Expressions is an expression parser and evaluation library.

Version: 0.1.7

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About this software

Fast Expressions is an expression parser and evaluation library.
High performance when parsing parser expressions is achieved by using a very fast parser.
Parsed expressions are wrapped into function calls.
High performance when evaluating expressions is achieved by not using any classes and using expression function execution directly.

Example

import 'dart:math';

import 'package:fast_expressions/fast_expressions.dart';

void main(List<String> args) {
  {
    const e = '1.isEven ? "Yes, 1 is even" : "No, 1 is odd"';
    final r = parseExpression(
      e,
      resolve: _resolve,
    );
    print(r());
  }

  {
    const e = '1 + 2 * 3';
    final r = parseExpression(e);
    print(r());
  }

  {
    const e = '1 + 2 * x';
    final r = parseExpression(
      e,
      context: {
        'x': 3,
      },
    );
    print(r());
  }

  {
    const e = '1 + 2 * x[y]';
    final r = parseExpression(
      e,
      context: {
        'x': [1, 2, 3],
        'y': 2,
      },
    );
    print(r());
  }

  {
    const e = '1 + 2 * add(1, 2)';
    final r = parseExpression(
      e,
      context: {
        'add': (num x, num y) => x + y,
      },
    );
    print(r());
  }

  {
    const e = '1 + 2 * sub(x: 7, y: 4)';
    final r = parseExpression(
      e,
      context: {
        'sub': ({required num x, required num y}) => x - y,
      },
    );
    print(r());
  }

  {
    const e = '1 + 2 * foo.add(1, 2)';
    final r = parseExpression(
      e,
      context: {
        'foo': Foo(),
      },
      resolve: _resolve,
    );
    print(r());
  }

  {
    const e = '1 + 2 * foo.list()[foo.add(1, 1)]';
    final r = parseExpression(
      e,
      context: {
        'foo': Foo(),
      },
      resolve: _resolve,
    );
    print(r());
  }

  {
    const e = '''
"Hello, " + friends[random()].name
''';
    final friends = [
      Person('Jack'),
      Person('Jerry'),
      Person('John'),
    ];
    final r = parseExpression(
      e,
      context: {
        'friends': friends,
        'random': () => Random().nextInt(friends.length - 1),
      },
      resolve: _resolve,
    );
    print(r());
  }
}

dynamic _resolve(dynamic object, String member) {
  Never error() {
    throw StateError("Invalid member '$member', object is $object");
  }

  if (object is Foo) {
    switch (member) {
      case 'add':
        return object.add;
      case 'list':
        return object.list;
    }
  }

  if (object is Person) {
    switch (member) {
      case 'name':
        return object.name;
    }
  }

  if (object is int) {
    switch (member) {
      case 'isEven':
        return object.isEven;
    }
  }

  error();
}

class Foo {
  num add(num x, num y) => x + y;

  List<num> list() => [1, 2, 3];
}

class Person {
  final String name;

  Person(this.name);
}

About the implementation of parsers

Parser are generated from PEG grammar.
Software used to generate parsers Pub Package
Below is the source code of the grammar.

%{

typedef Expression = dynamic Function();

String _escape(int charCode) {
    switch (charCode) {
      case 0x22:
        return '"';
      case 0x2f:
        return '/';
      case 0x5c:
        return '\\';
      case 0x62:
        return '\b';
      case 0x66:
        return '\f';
      case 0x6e:
        return '\n';
      case 0x72:
        return '\r';
      case 0x74:
        return '\t';
      default:
        throw StateError('Unable to escape charCode: $charCode');
    }
  }

}%

%%
  final Map<String, dynamic> context;

  final dynamic Function(dynamic object, String member)? resolve;

  ExpressionParser({
    this.context = const {},
    this.resolve,
  });

  Expression _binary(Expression? left, ({String op, Expression expr}) next) {
    final op = next.op;
    final right = next.expr;
    final l = left!;
    switch (op) {
      case '+':
        return () => l() + right();
      case '-':
        return () => l() - right();
      case '/':
        return () => l() / right();
      case '*':
        return () => l() * right();
      case '%':
        return () => l() % right();
      case '~/':
        return () => l() ~/ right();
      case '<<':
        return () => l() << right();
      case '>>':
        return () => l() >> right();
      case '>>>':
        return () => l() >>> right();
      case '&':
        return () => l() & right();
      case '^':
        return () => l() ^ right();
      case '|':
        return () => l() | right();
      case '>':
        return () => l() > right();
      case '>=':
        return () => l() >= right();
      case '<':
        return () => l() < right();
      case '<=':
        return () => l() <= right();
      case '||':
        return () => l() as bool || right() as bool;
      case '&&':
        return () => l() as bool && right() as bool;
      case '??':
        return () => l() ?? right();
      case '==':
        return () => l() == right();
      case '!=':
        return () => l() != right();
      default:
        throw StateError('Unknown operator: $op');
    }
  }

  Expression _prefix(String? operator, Expression operand) {
    if (operator == null) {
      return operand;
    }

    switch (operator) {
      case '-':
        return () => -operand();
      case '!':
        return () => !(operand() as bool);
      case '~':
        return () => ~operand();
      default:
        throw StateError('Unknown operator: $operator');
    }
  }

  Expression _postfix(
      Expression object, List<({String kind, dynamic arguments})> selectors) {
    for (final selector in selectors) {
      final kind = selector.kind;
      final arguments = selector.arguments;
      switch (kind) {
        case '.':
          final member = arguments as String;
          final object2 = object;
          object = () {
            final object3 = object2();
            if (resolve case final resolve?) {
              return resolve(object3, member);
            } else {
              throw StateError(
                  "Unable to resolve member '$member' for $object3");
            }
          };
          break;
        case '[':
          final index = arguments as dynamic Function();
          final object2 = object;
          object = () {
            final object3 = object2();
            final index2 = index();
            return object3[index2];
          };
          break;
        case '(':
          final object2 = object;
          final arguments2 =
              arguments as List<({String name, Expression expr})>;
          object = () {
            final object3 = object2() as Function;
            final positionalArguments = <dynamic>[];
            final namedArguments = <Symbol, dynamic>{};
            for (final element in arguments2) {
              final name = element.name;
              final expr = element.expr;
              if (name.isEmpty) {
                positionalArguments.add(expr());
              } else {
                if (namedArguments.containsKey(name)) {
                  throw StateError('Duplicate named argument: $name');
                }

                final key = Symbol(name);
                namedArguments[key] = expr();
              }
            }

            return Function.apply(object3, positionalArguments, namedArguments);
          };
          break;
        default:
          throw StateError('Unknown selector: $kind');
      }
    }

    return object;
  }
%%

Start = Spaces v:Expression Eof ;

Expression = Conditional ;

Expression
Conditional =
    e1:IfNull Question e2:Expression Colon e3:Expression { $$ = () => e1() as bool ? e2() : e3(); }
  / IfNull ;

Expression
IfNull = h:LogicalOr t:(op:IfNullOp ↑ expr:LogicalOr)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

IfNullOp = v:'??' Spaces ;

Expression
LogicalOr = h:LogicalAnd t:(op:LogicalOrOp ↑ expr:LogicalAnd)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

LogicalOrOp = v:'||' Spaces ;

Expression
LogicalAnd = h:Equality t:(op:LogicalAndOp ↑ expr:Equality)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

LogicalAndOp = v:'&&' Spaces ;

Expression
Equality = h:Relational t:(op:EqualityOp ↑ expr:Relational)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

EqualityOp = v:('==' / '!=') Spaces ;

Expression
Relational = h:BitwiseOr t:(op:RelationalOp ↑ expr:BitwiseOr)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

RelationalOp = v:('>=' / '>' / '<=' / '<') Spaces ;

Expression
BitwiseOr = h:BitwiseXor t:(op:BitwiseOrOp ↑ expr:BitwiseXor)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

BitwiseOrOp = !'||' v:'|' Spaces ;

Expression
BitwiseXor = h:BitwiseAnd t:(op:BitwiseXorOp ↑ expr:BitwiseAnd)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

BitwiseXorOp = v:'^' Spaces ;

Expression
BitwiseAnd = h:Shift t:(op:BitwiseAndOp ↑ expr:Shift)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

BitwiseAndOp = !'&&' v:'&' Spaces ;

Expression
Shift = h:Additive t:(op:ShiftOp ↑ expr:Additive)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

ShiftOp = v:('<<' / '>>>' / '>>') Spaces ;

Expression
Additive = h:Multiplicative t:(op:AdditiveOp ↑ expr:Multiplicative)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

AdditiveOp = v:('-' / '+') Spaces ;

Expression
Multiplicative = h:UnaryPrefix t:(op:MultiplicativeOp ↑ expr:UnaryPrefix)* { $$ = t.isEmpty ? h : t.fold(h, _binary); } ;

MultiplicativeOp = v:('/' / '*' / '%' / '~/') Spaces ;

UnaryPrefix = @expected('expression', UnaryPrefix_) ;

@inline
Expression
UnaryPrefix_ = op:UnaryPrefixOp? expr:UnaryPostfix { $$ = _prefix(op, expr); } ;

UnaryPrefixOp = v:('-' / '!' / '~') Spaces ;

Expression
UnaryPostfix = object:Primary selectors:Selector* { $$ = _postfix(object, selectors); } ;

({String kind, dynamic arguments})
Selector =
    kind:Dot arguments:Identifier_
  / kind:OpenBracket arguments:Expression CloseBracket
  / kind:OpenParenthesis arguments:Arguments CloseParenthesis ;

Arguments = @list(NamedArgument / PositionalArgument, Comma ↑ v:(NamedArgument / PositionalArgument)) ;

NamedArgument = name:Identifier_ Colon expr:Expression ;

PositionalArgument = name:'' expr:Expression ;

Primary =
    Number
  / Boolean
  / String
  / Null
  / Identifier
  / OpenParenthesis v:Expression CloseParenthesis ;

Expression
Null = 'null' Spaces { $$ = () => null; } ;

Expression
Boolean =
    'true' Spaces { $$ = () => true; }
  / 'false' Spaces { $$ = () => false; } ;

Expression
Number = v:$(
  [-]?
  ([0] / [1-9][0-9]*)
  ([.] [0-9]+)?
  ([eE] ↑ [-+]? [0-9]+)?
  ) Spaces {
    final n = num.parse(v);
    $$ = () => n;
  } ;

@inline
String
EscapeChar = c:["/bfnrt\\] { $$ = _escape(c); } ;

@inline
String
EscapeHex = 'u' v:HexNumber { $$ = String.fromCharCode(v); } ;

HexNumber = @indicate('Expected 4 digit hex number', HexNumber_) ;

@inline
int
HexNumber_ = v:$([0-9A-Za-z]{4}) { $$ = int.parse(v, radix: 16); } ;

String
StringChars =
    $[\u{20}-\u{21}\u{23}-\u{5b}\u{5d}-\u{10ffff}]+
  / '\\' v:(EscapeChar / EscapeHex) ;

String
StringRaw = '"' v:StringChars* DoubleQuote { $$ = v.join(); } ;

Expression
String = v:StringRaw { $$ = () => v; } ;

@inline
String
Identifier_ = v:@expected('identifier', $([a-zA-Z_$] [a-zA-Z_$0-9]*)) Spaces ;

Expression
Identifier = v:Identifier_ {
    $$ = () {
      if (!context.containsKey(v)) {
        throw StateError("Variable '$v' not found");
      }
      return context[v];
    };
  } ;

Eof = !. ;

CloseBracket = v:']' Spaces ;

CloseParenthesis = v:')' Spaces ;

Colon = v:':' Spaces ;

Comma = v:',' Spaces ;

Dot = v:'.' Spaces ;

DoubleQuote = v:'"' Spaces ;

OpenBracket = v:'[' Spaces ;

OpenParenthesis = v:'(' Spaces ;

Question = v:'?' Spaces ;

Spaces = [ \n\r\t]* ;

Libraries

fast_expressions