Skip to main content

Load

rascal-0.40.17

Synopsis​

Convert a Pico parse tree into a Pico abstract syntax tree.

Examples​

The mapping between parse tree and abstract sybtax tree is achieved as follows:

module demo::lang::Pico::Load

import Prelude;
import demo::lang::Pico::Syntax;
import demo::lang::Pico::Abstract;

public PROGRAM load(str txt)      ❶  
    =     ❸     implode(#PROGRAM,     ❷     parse(#start[Program], txt).top);

Notes:

  • ❶ The function load takes a string as argument (supposedly the source code of a Pico program) and returns a value of type PROGRAM, the abstract syntax tree of the input program. In case the input program is syntactically incorrect, a ParseError exception will be thrown, see RuntimeException.

  • ❷ parse(#start[Program], txt): parse txt according to the non-terminal Program.

    • Note that #start[Program] is a reified type. The # operator turns a type literal into an ordinary Rascal value, which is then used by the parse function to generate a parser.
    • We use #start[Program] instead of directly #Program because the automatic start rule accepts whitespace before and after the program. See reified types for more information about reifying types and grammars. The parse function returns a Parse Tree of the input program.

  • ❸ implode(#PROGRAM, parse(#Program, txt)): Transform the parse returned by parse into an abstract syntax tree of type PROGRAM. The Implode function performs the automatic mapping between elements in the parse tree and their counterpart in the abstract syntax.

The function load can be used as follows:

rascal>import demo::lang::Pico::Load;
ok
rascal>load("begin declare x : natural; x := 3 end");
PROGRAM: program(
  [decl(
      "x",
      natural(
        src=|unknown:///|(18,7,<1,18>,<1,25>),
        comments=()),
      src=|unknown:///|(14,11,<1,14>,<1,25>),
      comments=())],
  [asgStat(
      "x",
      natCon(
        3,
        src=|unknown:///|(32,1,<1,32>,<1,33>),
        comments=()),
      src=|unknown:///|(27,6,<1,27>,<1,33>),
      comments=())],
  src=|unknown:///|(0,37,<1,0>,<1,37>),
  comments=())

Observe how the various parts of the abstract syntax tree are annotated with location attributes.