Function flexi_parse::parse

source · 
pub fn parse<T: Parse>(tokens: TokenStream) -> Result<T>
Expand description

Parses the given tokens into the syntax tree node T.

This function ignores all whitespace.

Examples found in repository?
examples/calc.rs (line 90)
82
83
84
85
86
87
88
89
90
91
92
93
94

fn primary(input: ParseStream<'_>) -> Result<Expr> {
    let lookahead = input.lookahead();
    if lookahead.peek(token::LitFloat) {
        Ok(Expr::Num(input.parse::<token::LitFloat>()?.value()))
    } else if lookahead.peek(token::LitInt) {
        Ok(Expr::Num(input.parse::<token::LitInt>()?.value() as f64))
    } else if lookahead.peek(token::LeftParen) {
        let group: Group<Parentheses> = input.parse()?;
        parse(group.into_token_stream())
    } else {
        Err(lookahead.error())
    }
}
More examples
Hide additional examples
examples/lox.rs (line 310)
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566

    fn primary(input: ParseStream<'_>) -> Result<Self> {
        let lookahead = input.lookahead();
        if lookahead.peek(kw::keyword_false) {
            Ok(Expr::Literal(Literal::False(input.parse()?)))
        } else if lookahead.peek(kw::keyword_true) {
            Ok(Expr::Literal(Literal::True(input.parse()?)))
        } else if lookahead.peek(kw::keyword_nil) {
            Ok(Expr::Literal(Literal::Nil(input.parse()?)))
        } else if lookahead.peek(LitFloat) {
            Ok(Expr::Literal(Literal::Float(input.parse()?)))
        } else if lookahead.peek(LitInt) {
            Ok(Expr::Literal(Literal::Int(input.parse()?)))
        } else if lookahead.peek(LitStr) {
            Ok(Expr::Literal(Literal::String(input.parse()?)))
        } else if input.peek(kw::keyword_super) {
            Ok(Expr::Super {
                keyword: input.parse()?,
                method: input.parse()?,
            })
        } else if input.peek(kw::keyword_this) {
            Ok(Expr::This(input.parse()?))
        } else if lookahead.peek(Ident) {
            Ok(Expr::Variable(kw::ident(input)?))
        } else if lookahead.peek(Punct!["("]) {
            let group: Group<Parentheses> = input.parse()?;
            parse(group.into_token_stream())
        } else {
            Err(lookahead.error())
        }
    }
}

impl Parse for Expr {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        Expr::assignment(input)
    }
}

#[allow(dead_code)]
#[derive(Debug, Clone, PartialEq)]
struct Function {
    name: Ident,
    params: Vec<Ident>,
    body: Vec<Stmt>,
}

impl Parse for Function {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        let name: Ident = input.parse()?;
        let mut contents: Group<Parentheses> = input.parse()?;
        contents.remove_whitespace();
        let Parentheses(span) = contents.delimiters();
        let params: Punctuated<Ident, Punct![","]> =
            Punctuated::parse_separated.parse(contents.into_token_stream())?;
        let params: Vec<_> = params.into_iter().collect();
        if params.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 parameters".to_string(),
                span,
                1,
            ));
        }
        let mut contents: Group<Braces> = input.parse()?;
        contents.remove_whitespace();
        let body = block.parse(contents.into_token_stream())?;
        Ok(Function { name, params, body })
    }
}

#[allow(dead_code)]
#[derive(Debug, Clone, PartialEq)]
enum Stmt {
    Block(Vec<Stmt>),
    Class {
        name: Ident,
        superclass: Option<Ident>,
        methods: Vec<Function>,
    },
    Expr(Expr),
    Function(Function),
    If {
        condition: Expr,
        then_branch: Box<Stmt>,
        else_branch: Option<Box<Stmt>>,
    },
    Print(Expr),
    Return {
        keyword: kw::keyword_return,
        value: Expr,
    },
    Variable {
        name: Ident,
        initialiser: Expr,
    },
    While {
        condition: Expr,
        body: Box<Stmt>,
    },
}

fn block(input: ParseStream<'_>) -> Result<Vec<Stmt>> {
    let mut statements = vec![];

    while !input.is_empty() {
        statements.push(Stmt::declaration(input)?);
    }

    Ok(statements)
}

impl Stmt {
    fn declaration(input: ParseStream<'_>) -> Result<Self> {
        if input.peek(kw::keyword_class) {
            Stmt::class_declaration(input)
        } else if input.peek(kw::keyword_fun) {
            let _: kw::keyword_fun = input.parse()?;
            Ok(Stmt::Function(Function::parse(input)?))
        } else if input.peek(kw::keyword_var) {
            Stmt::var_declaration(input)
        } else {
            Stmt::statement(input)
        }
    }

    fn class_declaration(input: ParseStream<'_>) -> Result<Self> {
        let _: kw::keyword_class = input.parse()?;
        let name: Ident = input.parse()?;

        let superclass = if input.peek(Punct!["<"]) {
            let _: Punct!["<"] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let mut contents: Group<Braces> = input.parse()?;
        contents.remove_whitespace();
        let methods = parse_repeated.parse(contents.into_token_stream())?;

        Ok(Stmt::Class {
            name,
            superclass,
            methods,
        })
    }

    fn var_declaration(input: ParseStream<'_>) -> Result<Self> {
        let _: kw::keyword_var = input.parse()?;

        let name = kw::ident(input)?;

        let initialiser = if input.peek(Punct!["="]) {
            let _: Punct!["="] = input.parse()?;
            input.parse()?
        } else {
            Expr::Literal(Literal::Nil(kw::keyword_nil::new(input)))
        };

        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Variable { name, initialiser })
    }

    fn statement(input: ParseStream<'_>) -> Result<Self> {
        if input.peek(kw::keyword_if) {
            Stmt::if_statement(input)
        } else if input.peek(kw::keyword_for) {
            Stmt::for_statement(input)
        } else if input.peek(kw::keyword_print) {
            Stmt::print_statement(input)
        } else if input.peek(kw::keyword_return) {
            Stmt::return_statement(input)
        } else if input.peek(kw::keyword_while) {
            Stmt::while_statement(input)
        } else if input.peek(Punct!["{"]) {
            let mut group: Group<Braces> = input.parse()?;
            group.remove_whitespace();
            Ok(Stmt::Block(block.parse(group.into_token_stream())?))
        } else {
            Stmt::expression_statement(input)
        }
    }

    fn for_statement(input: ParseStream<'_>) -> Result<Self> {
        struct ForInner(Option<Stmt>, Expr, Option<Expr>);

        impl Parse for ForInner {
            fn parse(input: ParseStream<'_>) -> Result<Self> {
                let initialiser = if input.peek(Punct![";"]) {
                    let _: Punct![";"] = input.parse()?;
                    None
                } else if input.peek(kw::keyword_var) {
                    Some(Stmt::var_declaration(input)?)
                } else {
                    Some(Stmt::expression_statement(input)?)
                };

                let condition = if input.peek(Punct![";"]) {
                    Expr::Literal(Literal::True(kw::keyword_true::new(input)))
                } else {
                    Expr::parse(input)?
                };
                let _: Punct![";"] = input.parse()?;

                let increment = if input.is_empty() {
                    None
                } else {
                    Some(Expr::parse(input)?)
                };

                Ok(ForInner(initialiser, condition, increment))
            }
        }

        let _: kw::keyword_for = input.parse()?;

        let mut inner: Group<Parentheses> = input.parse()?;
        inner.remove_whitespace();
        let ForInner(initialiser, condition, increment) = parse(inner.into_token_stream())?;

        let mut body = Stmt::statement(input)?;

        if let Some(increment) = increment {
            body = Stmt::Block(vec![body, Stmt::Expr(increment)]);
        }

        body = Stmt::While {
            condition,
            body: Box::new(body),
        };

        if let Some(initialiser) = initialiser {
            body = Stmt::Block(vec![initialiser, body]);
        }

        Ok(body)
    }

    fn if_statement(input: ParseStream<'_>) -> Result<Self> {
        let _: kw::keyword_if = input.parse()?;
        let condition: Group<Parentheses> = input.parse()?;
        let condition = parse(condition.into_token_stream())?;

        let then_branch = Box::new(Stmt::statement(input)?);
        let else_branch = if input.peek(kw::keyword_else) {
            Some(Box::new(Stmt::statement(input)?))
        } else {
            None
        };

        Ok(Stmt::If {
            condition,
            then_branch,
            else_branch,
        })
    }

    fn print_statement(input: ParseStream<'_>) -> Result<Self> {
        let _: kw::keyword_print = input.parse()?;
        let value = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Print(value))
    }

    fn return_statement(input: ParseStream<'_>) -> Result<Self> {
        let keyword: kw::keyword_return = input.parse()?;
        let value = if input.peek(Punct![";"]) {
            Expr::Literal(Literal::Nil(kw::keyword_nil::new(input)))
        } else {
            input.parse()?
        };
        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Return { keyword, value })
    }

    fn while_statement(input: ParseStream<'_>) -> Result<Self> {
        let _: kw::keyword_while = input.parse()?;
        let condition: Group<Parentheses> = input.parse()?;
        let condition = parse(condition.into_token_stream())?;
        let body = Box::new(Stmt::statement(input)?);

        Ok(Stmt::While { condition, body })
    }