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package examples.parsing.lambda
import scala.util.parsing.input.Reader
import scala.util.parsing.combinator.lexical.StdLexical
import scala.util.parsing.combinator.syntactical.StdTokenParsers
import scala.util.parsing.combinator.ImplicitConversions
/**
* Parser for an untyped lambda calculus
*
* @author Miles Sabin (adapted slightly by Adriaan Moors)
*/
trait TestParser extends StdTokenParsers with ImplicitConversions with TestSyntax
{
type Tokens = StdLexical
val lexical = new StdLexical
lexical.reserved ++= List("unit", "let", "in", "if", "then", "else")
lexical.delimiters ++= List("=>", "->", "==", "(", ")", "=", "\\", "+", "-", "*", "/")
def name : Parser[Name] = ident ^^ Name
// meaning of the argumens to the closure during subsequent iterations
// (...(expr2 op1 expr1) ... op1 expr1)
// ^a^^^ ^o^ ^b^^^
// ^^^^^^^a^^^^^^^ ^o^ ^^b^^
def expr1 : Parser[Term] =
chainl1(expr2, expr1, op1 ^^ {o => (a: Term, b: Term) => App(App(o, a), b)})
def expr2 : Parser[Term] =
chainl1(expr3, expr2, op2 ^^ {o => (a: Term, b: Term) => App(App(o, a), b)})
def expr3 : Parser[Term] =
chainl1(expr4, expr3, op3 ^^ {o => (a: Term, b: Term) => App(App(o, a), b)})
def expr4 : Parser[Term] =
( "\\" ~> lambdas
| ("let" ~> name) ~ ("=" ~> expr1) ~ ("in" ~> expr1) ^^ flatten3(Let)
| ("if" ~> expr1) ~ ("then" ~> expr1) ~ ("else" ~> expr1) ^^ flatten3(If)
| chainl1(aexpr, success(App(_: Term, _: Term)))
)
def lambdas : Parser[Term] =
name ~ ("->" ~> expr1 | lambdas) ^^ flatten2(Lam)
def aexpr : Parser[Term] =
( numericLit ^^ (_.toInt) ^^ Lit
| name ^^ Ref
| "unit" ^^^ Unit()
| "(" ~> expr1 <~ ")"
)
def op1 : Parser[Term] =
"==" ^^^ Ref(Name("=="))
def op2 : Parser[Term] =
( "+" ^^^ Ref(Name("+"))
| "-" ^^^ Ref(Name("-"))
)
def op3 : Parser[Term] =
( "*" ^^^ Ref(Name("*"))
| "/" ^^^ Ref(Name("/"))
)
def parse(r: Reader[char]) : ParseResult[Term] =
phrase(expr1)(new lexical.Scanner(r))
}
|
