Layout in Rascal

Question

When I import the Lisra recipe,

import demo::lang::Lisra::Syntax;

This creates the syntax:

layout Whitespace      = [\\t-\\n\\r         


        

Answer 1

When you define a start non-terminal Rascal defines two non-terminals in one go:

rascal>start syntax A = "a";
ok

One non-terminal is A, the other is start[A]. Given a layout non-terminal in scope, say L, the latter is automatically defined by (something like) this rule:

syntax start[A] = L before A top L after;

If you call a parser or wish to parse a concrete fragment, you can use either non-terminal:

parse(#start[A], " a ") // parse using the start non-terminal and extra layout
parse(A, "a") // parse only an A
(start[A]) ` a ` // concrete fragment for the start-non-terminal
(A) `a` // concrete fragment for only an A
[start[A]] " a "
[A] "a"