Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision Next revision Both sides next revision | ||
|
cc19:scallion [2019/10/09 12:20] georg.schmid Typos |
cc19:scallion [2019/10/09 12:24] georg.schmid Typos |
||
|---|---|---|---|
| Line 26: | Line 26: | ||
| ==== Setup ==== | ==== Setup ==== | ||
| - | In Scallion, parsers are called defined within a trait called ''%%Syntaxes%%''. This trait takes as parameters two types: | + | In Scallion, parsers are defined within a trait called ''%%Syntaxes%%''. This trait takes as parameters two types: |
| * The type of tokens, | * The type of tokens, | ||
| Line 47: | Line 47: | ||
| ==== Writing Parsers ==== | ==== Writing Parsers ==== | ||
| - | When writing a parser using parser combinators, one defines many smaller parsers and combine them together into more and more complex parsers. The top-level, most complex, of those parser then defines the entire syntax for the language. In our case, that top-level parser will be called ''%%program%%''. | + | When writing a parser using parser combinators, one defines many smaller parsers and combines them together into more and more complex parsers. The top-level, most complex, of those parser then defines the entire syntax for the language. In our case, that top-level parser will be called ''%%program%%''. |
| All those parsers are objects of the type ''%%Syntax[A]%%''. The type parameter ''%%A%%'' indicates the type of values produced by the parser. For instance, a parser of type ''%%Syntax[Int]%%'' produces ''%%Int%%''s and a parser of type ''%%Syntax[Expr]%%'' produces ''%%Expr%%''s. Our top-level parser has the following signature: | All those parsers are objects of the type ''%%Syntax[A]%%''. The type parameter ''%%A%%'' indicates the type of values produced by the parser. For instance, a parser of type ''%%Syntax[Int]%%'' produces ''%%Int%%''s and a parser of type ''%%Syntax[Expr]%%'' produces ''%%Expr%%''s. Our top-level parser has the following signature: | ||
| Line 54: | Line 54: | ||
| lazy val program: Parser[Program] = ... | lazy val program: Parser[Program] = ... | ||
| </code> | </code> | ||
| - | Contrarily to the types of tokens and token kinds, which are fixed, the type of value produced is a type parameter of the various ''%%Syntax%%''s. This allows your different parsers to produce different type of values. | + | Contrary to the types of tokens and token kinds, which are fixed, the type of values produced is a type parameter of the various ''%%Syntax%%''s. This allows your different parsers to produce different types of values. |
| The various parsers are stored as ''%%val%%'' members of the ''%%Parser%%'' object. In the case of mutually dependent parsers, we use ''%%lazy val%%'' instead. | The various parsers are stored as ''%%val%%'' members of the ''%%Parser%%'' object. In the case of mutually dependent parsers, we use ''%%lazy val%%'' instead. | ||