calc.peg

%{
//ignore_for_file: prefer_conditional_assignment, prefer_final_locals

import 'package:source_span/source_span.dart';

void main() {
  const source = ' 1 + 2 * 3 + x ';
  final result = calc(source, {'x': 5});
  print(result);
}

int calc(String source, Map<String, int> vars) {
  final parser = CalcParser(vars);
  final state = State(source);
  final result = parser.parseStart(state);
  if (result == null) {
    final file = SourceFile.fromString(source);
    throw FormatException(state
        .getErrors()
        .map((e) => file.span(e.start, e.end).message(e.message))
        .join('\n'));
  }

  return result.$1;
}

}%

%%

Map<String, int> vars = {};

CalcParser(this.vars);

%%

`int`
Start =>
  S
  $ = Expr
  EOF

`int`
Expr('expression') =>
  Sum

`int`
Sum =>
  $ = Product
  @while (*) {
    [+] S
    r = Product
    { $ += r; }
    ----
    [-] S
    r = Product
    { $ -= r; }
  }

`int`
Product =>
  $ = Value
  @while (*) {
    [*] S
    r = Value
    { $ *= r; }
    ----
    [/] S
    r = Value
    { $ ~/= r; }
  }

`int`
Value('expression') => (
  NUMBER
  ----
  i = ID
  $ = { vars[i]! }
  ----
  '(' S
  $ = Expr
  ')' S
)

`int`
NUMBER =>
  n = <[0-9]+>
  S
  $ = { int.parse(n) }

`String`
ID =>
  $ = <[a-zA-Z]>
  S

`void`
EOF('end of file') =>
  ! .

`void`
S => [ \t\r\n]*