14fd434 · urbit.org · git.iko.soy

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14fd434JONATHAN PAPROCKI6 years ago

tutorials/arvo/parsing.md+16−13

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unifiedsplit

@@ -39,16 +39,16 @@ that are plugged into one another in various ways to perform the desired task.

40The basic building blocks, or primitives, are parsers that read only a

41single character. There are frequently a few types of possible input characters,

42−such as letters, numbers, and symbols. For example, `parse("1", integer)` calls

42+such as letters, numbers, and symbols. For example, `(parse "1" integer)` calls

43the parsing routine on the string `"1"` and looks for an integer, and so it

44returns the integer `1`. However, taking into account what was said above about

45parsers returning the unparsed portion of the string as well, we should

46represent this return as a tuple. So we should expect something like this:

47```

48−> parse("1", integer)

48+> (parse "1" integer)

49−(1, "")

49+[1 ""]

50−> parse("123", integer)

50+> (parse "123" integer)

51−(1, "23")

51+[1 "23"]

52```

53What if we wish to parse the rest of the string? We would need to apply the

54`parse` function again:

@@ -57,6 +57,10 @@ What if we wish to parse the rest of the string? We would need to apply the

57(12, "3")

58> parse(parse(parse("123", integer), integer), integer)

59(123, "")

60+> (parse (parse "123" integer) integer)

61+[12 "3"]

62+> (parse (parse (parse "123" integer) integer) integer)

63+[123 ""]

60```

64```

61So we see that we can parse strings larger than one character by stringing

65So we see that we can parse strings larger than one character by stringing

62together parsing functions for single characters. Thus in addition to parsing

66together parsing functions for single characters. Thus in addition to parsing

@@ -179,9 +183,7 @@ parser has not advanced since parsing failed. `q.edg` is null, indicating that

179parsing has failed.

183parsing has failed.

180

184

181Later we will use [+star](#star) to string together a sequence of `+just`s in

185Later we will use [+star](#star) to string together a sequence of `+just`s in

182−order to parse multiple characters at once. However, it should be noted that

186+order to parse multiple characters at once.

183−`+jest`, which is covered next, ought to be used in favor of `+just`, which is

184−mostly included here for pedagogical reasons.

185

187

186### `+jest`

188### `+jest`

187

189

@@ -531,14 +533,14 @@ your `gen/` folder.

531 (ifix [lit rit] expr)

533 (ifix [lit rit] expr)

532 ==

534 ==

533++ turm

535++ turm

534− %+ knee @ud

536+ %+ knee *@ud

535 |. ~+

537 |. ~+

536 ;~ pose

538 ;~ pose

537 ((slug mul) tar ;~(pose factor turm))

539 ((slug mul) tar ;~(pose factor turm))

538 factor

540 factor

539 ==

541 ==

540++ expr

542++ expr

541− %+ knee @ud

543+ %+ knee *@ud

542 |. ~+

544 |. ~+

543 ;~ pose

545 ;~ pose

544 ((slug add) lus ;~(pose turm expr))

546 ((slug add) lus ;~(pose turm expr))

@@ -556,7 +558,7 @@ for expressions.

556

558

557```hoon

559```hoon

558++ factor

560++ factor

559− %+ knee @ud

561+ %+ knee *@ud

560 |. ~+

562 |. ~+

561 ;~ pose

563 ;~ pose

562 dem

564 dem

@@ -623,8 +625,9 @@ for expressions, we just need to swap `lus` for `tar`, `add` for `mul`, and

623

625

624```hoon

626```hoon

625++ expr

627++ expr

626− %+ knee *int

628+ %+ knee *@ud

629+ |. ~+

627− |. ~+ ;~ pose

630+ ;~ pose

628 ((slug add) lus ;~(pose turm expr))

631 ((slug add) lus ;~(pose turm expr))

629 turm

632 turm

630 ==

633 ==