package org.lambdanantes.lcgoji;

import org.junit.Test;
import org.lambdanantes.lcgoji.ast.Term;
import org.lambdanantes.lcgoji.ast.Var;

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;
import static org.lambdanantes.lcgoji.LCEvaluator.evaluate;
import static org.lambdanantes.lcgoji.ast.Abs.IDENTITY;
import static org.lambdanantes.lcgoji.ast.Abs.λ;
import static org.lambdanantes.lcgoji.ast.App.apply;
import static org.lambdanantes.lcgoji.ast.Var.var;

public class LCEvaluatorTest {

    Var x = var("x");
    Var y = var("y");
    Var z = var("z");

    @Test
    public void l_evaluation_d_une_variable_rend_la_meme_variable() {
        // evaluate(x) == x
        assertEvalTo(x, x);
    }

    @Test
    public void l_evaluation_d_une_abstraction_rend_la_meme_abstraction() {
        // evaluate(λx.x) == λx.x
        assertEvalTo(IDENTITY, IDENTITY);
    }

    @Test
    public void l_evaluation_de_l_application_de_deux_vars_rend_la_meme_application() {
        // evaluate(x y) == x y
        assertEvalTo(apply(x, y), apply(x, y));
    }

    @Test
    public void l_evaluation_de_l_application_de_l_identite_sur_un_argument_rend_l_argument() {
        // evaluate((λx.x) y) == y
        assertEvalTo(apply(IDENTITY, y), y);
    }

    @Test
    public void l_evaluation_de_l_application_d_une_abstraction_substitue_son_argument() {
        // evaluate((λx.x x) y ) == y y
        assertEvalTo(apply(λ("x", apply(x, x)), y), apply(y, y));
    }

    @Test
    public void l_evaluation_de_l_application_d_une_abstraction_d_abstraction_substitue_recursivement_son_argument() {
        // evaluate((λx.λy.x) z) == λy.z
        assertEvalTo(apply(λ("x", λ("y", x)), z), λ("y", z));
    }

    @Test
    public void l_evaluation_de_l_application_d_une_abstraction_ne_substitue_pas_ses_variables_libres() {
        // evaluate((λx.y) z) == y
        assertEvalTo(apply(λ("x", y), z), y);
    }

    @Test
    public void l_evaluation_de_l_application_d_une_abstraction_d_abstraction_ne_substitue_pas_les_variables_redefinies() {
        // evaluate((λx.λx.x) z) == λx.x
        assertEvalTo(apply(λ("x", λ("x", x)), z), λ("x", x));
    }

    /////

    private static void assertEvalTo(Term termToEvaluate, Term result) {
        assertThat(evaluate(termToEvaluate), is(result));
    }
}