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module demo::lang::Pico::Eval

rascal-0.34.0

Usage​

import demo::lang::Pico::Eval;

Dependencies​

import demo::lang::Pico::Abstract;
import demo::lang::Pico::Load;

data PicoValue​

data PicoValue  
     = natval(int n)
     | strval(str s)
     | errorval(loc l, str msg)
     ;

alias VENV​

map[PicoId, PicoValue]

function evalExp​

Evaluate Expressions


     ❸      PicoValue evalExp(exp:natCon(int N), VENV env) = natval(N);

PicoValue evalExp(exp:strCon(str S), VENV env) = strval(S);

PicoValue evalExp(exp:id(PicoId Id), VENV env)  = 
    env[Id]?  ? env[Id] : errorval(exp.src, "Uninitialized variable <Id>");

PicoValue evalExp(exp:add(EXP E1, EXP E2), VENV env) = 
   (natval(n1) := evalExp(E1, env) && 
    natval(n2) := evalExp(E2, env)) ? natval(n1 + n2)
                                    : errorval(exp.src, "+ requires natural arguments");

PicoValue evalExp(exp:sub(EXP E1, EXP E2), VENV env) = 
   (natval(n1) := evalExp(E1, env) && 
    natval(n2) := evalExp(E2, env)) ? natval(n1 - n2)
                                    : errorval(exp.src, "- requires natural arguments");

PicoValue evalExp(exp:conc(EXP E1, EXP E2), VENV env) = 
   (strval(s1) := evalExp(E1, env) && 
    strval(s2) := evalExp(E2, env)) ? strval(s1 + s2)
                                    : errorval(exp.src, "|| requires string arguments");

function evalStat​

Evaluate a statement


     ❸      VENV evalStat(stat:asgStat(PicoId Id, EXP Exp), VENV env) {
  env[Id] = evalExp(Exp, env);
  return env;
}

VENV evalStat(stat:ifElseStat(EXP Exp, 
                              list[STATEMENT] Stats1,
                              list[STATEMENT] Stats2),
              VENV env) =
  evalStats(evalExp(Exp, env) != natval(0) ? Stats1 : Stats2, env);

VENV evalStat(stat:whileStat(EXP Exp, 
                             list[STATEMENT] Stats1),
              VENV env) {
    while(evalExp(Exp, env) != natval(0)){
       env = evalStats(Stats1, env);
    }
    return env;
}

function evalStats​

Evaluate a list of statements


     ❸      VENV evalStats(list[STATEMENT] Stats1, VENV env) {
  for(S <- Stats1){
      env = evalStat(S, env);
  }
  return env;
}

function evalDecls​

Evaluate declarations


     ❸      VENV evalDecls(list[DECL] Decls) =
    ( Id : (tp == demo::lang::Pico::Abstract::natural() ? natval(0) : strval(""))  
    | decl(PicoId Id, TYPE tp) <- Decls
    );

function evalProgram​

Evaluate a parsed Pico program


     ❸      VENV evalProgram(PROGRAM P){
  if(program(list[DECL] Decls, list[STATEMENT] Series) := P){
     VENV env = evalDecls(Decls);
     return evalStats(Series, env);
  } else
    throw "Cannot happen";
}

function evalProgram​

Parse and evaluate a Pico program


     ❹      VENV evalProgram(str txt) = evalProgram(load(txt));