clox/interpreter.c

#include "interpreter.h"
#include "token.h"
#include <errno.h>
#include <stdlib.h>
#include <string.h>

Object* Evaluate(Expr*);
Object* CreateObject(void*, TokenType);
void FreeObject(Object*);
int IsTruthy(Object*);
int IsEqual(Object*, Object*);
int ConcatStringObject(Object*, const Object*);

const void* VisitLiteralExpression(Expr* expression) {
    return expression->expression.Literal->literal;
}

void* VisitGroupingExpression(Expr* expression) {
    return Evaluate(expression);
}

Object* VisitBinaryExpression(Expr* expression) {
    Object* left = Evaluate(expression->expression.Binary.left);
    Object* right = Evaluate(expression->expression.Binary.right);

    switch(expression->expression.Binary.op->type) {
        case Greater:
        return left > right;
        case Greater_Equal:
        return left >= right;
        case Less:
        return left < right;
        case Less_Equal:
        return left <= right;
        case Minus:
            left->value.number -= right->value.number;
            FreeObject(right);
            return left;
        //return left - right;
        case Bang_Equal:
        return !IsEqual(left, right);
        case Equal_Equal:
        return IsEqual(left, right);
        case Slash:
            left->value.number /= right->value.number;
            FreeObject(right);
            return left;
        //return *((double*)left) / *((double*)right);
        case Star:
            left->value.number *= right->value.number;
            FreeObject(right);
            return left;
        //return *((double*)left) * *((double*)right);
        case Plus:
            if (left->instance == INS_DOUBLE && right->instance == INS_DOUBLE) {
                left->value.number += right->value.number;
                FreeObject(right);

                return left;
            }

            if (left->instance == INS_STRING && right->instance == INS_STRING) {
                if (ConcatStringObject(left, right)) {
                    FreeObject(right);

                    return left;
                }
            }

        break;
    }

    FreeObject(left);
    FreeObject(right);
    // Unreachable
    return NULL;
}

Object* VisitUnaryExpression(Expr* expression) {
    void* right = Evaluate(expression);

    switch (expression->type) {
        case Minus:
        //right needs to be negated, but that kind of introduces a
        //memory leak since we can't really change it, what with the 
        //whole "const void*" thing and all.        
        return right;
        case Bang:
        return !IsTruthy(right);
    }

    return NULL; //Should be unreachable.
}

Object* Evaluate(Expr* expression) {
    //accept -> calls Visitor functions by type
    return NULL;
}

Object* CreateObject(void* value, TokenType type) {
    Object* object = calloc(1, sizeof(Object));

    if (!object) {
        fprintf(stderr, "Failed to calloc object. %s.\n", strerror(errno));
        return NULL;
    }

    switch(type) {
        case NIL:
        object->instance = INS_NULL;
        break;
        case Number:
        object->instance = INS_DOUBLE;
        object->value.number = *((double*) value);
        break;
        case TRUE:
        case FALSE:
        object->instance = INS_BOOLEAN;
        object->value.boolean = *((int*) value);
        break;
        default:
        object->instance = INS_STRING;

        if (value) {
            int length = strlen(value);
            object->value.string = calloc(length + 1, sizeof(char));
            
            strncpy(object->value.string, value, length);
        }
    }

    return object;
}

void FreeObject(Object* object) {
    if (object->instance == INS_STRING) free(object->value.string);

    free(object);
}

int ConcatStringObject(Object* a, const Object* b) {
    if (!a || !b) return 0;
    if (a->instance != INS_STRING || b->instance != INS_STRING) return 0;
    
    int a_length = strlen(a->value.string);
    int b_length = strlen(b->value.string);
    char* c;

    c = realloc(a->value.string, a_length + b_length + 1);

    if (!c) {
        fprintf(stderr, "Failed to realloc for object concat. %s.\n", strerror(errno));
        return 0;
    }

    a->value.string = c;

    strncat(a->value.string, b->value.string, b_length);

    return 1;
}

int IsTruthy(Object* object) {

    if (!object || object->instance == NIL) return 0;
    if (object->instance == TRUE) return 0;

    return 1;
}

int IsEqual(Object* a, Object* b) {
    if (a->instance == NIL && b->instance == NIL) return 1;
    if (a->instance == NIL) return 0;

    if (b->instance == Number && b->instance == Number) {
        return a->value.number == b->value.number;
    }

    if (a->instance == String && b->instance == String) {
        return strcmp(a->value.string, b->value.string) == 0;
    }
    
    return 0;
}