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eval.c
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eval.c
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#include "eval.h"
#include "stmt.h"
#include "terp.h"
#include "khash.h"
#include "parse.h"
#include "lex.h"
#define NIL nil()
// nil singleton
Element *_nil = NULL;
Element *nil() {
if (_nil == NULL) {
_nil = malloc(sizeof(Element));
_nil->type = tNIL;
}
return _nil;
}
// TODO: alias Element to something more appropriate
Element *evaluate(ParseNode *stmt, State *state) {
khiter_t k = 0;
Element *left, *right, *returnValue;
int ret;
switch(stmt->sType) {
case sASSIGN:
// TODO: undeclared variables should not be added to state
// TODO: set in stone types, or no? (Default: no)
// add var to state if it doesn't exist already
if (!exists(state->h, stmt->children[0]->name)) {
// set variable type to expression's value type
stmt->children[0]->vType = stmt->children[1]->vType;
k = kh_put(32, state->h, stmt->children[0]->name, &ret);
// no need to evaluate variable, its value is being destroyed
} else {
// variable already exists in hashmap
k = kh_get(32, state->h, stmt->children[0]->name);
}
kh_val(state->h, k) = evaluate(stmt->children[1], state);
returnValue = malloc(sizeof(Element));
memcpy(returnValue, kh_val(state->h, k), sizeof(Element));
return returnValue;
case sIF:
// evaluate branch iff cond = true
returnValue = evaluate(stmt->children[0], state);
if (returnValue->type == tNIL)
return NIL;
if (returnValue->value.boolean) {
// returnValue can't be nil, so free it
free(returnValue);
return evaluate(stmt->children[1], state);
} else {
// there's no else branch of the statement, so its value becomes nil
free(returnValue);
return NIL;
}
case sIFELSE:
// evaluate b_true if cond = true else evaluate b_false
returnValue = evaluate(stmt->children[0], state);
if (returnValue->type == tNIL)
return NIL;
if (returnValue->value.boolean) {
free(returnValue);
return evaluate(stmt->children[1], state);
} else {
free(returnValue);
return evaluate(stmt->children[2], state);
}
case sBOOL:
returnValue = malloc(sizeof(Element));
returnValue->type = tBOOL;
// if no children, then it's true/false, no evaluation
if (stmt->children == NULL) {
returnValue->value.boolean = stmt->value.boolean;
return returnValue;
}
// evaluate and store 0/1 in stmt->value
left = evaluate(stmt->children[0], state);
right = evaluate(stmt->children[1], state);
// TODO: handle real numbers
switch(stmt->op.boolop) {
case bLESSTHAN:
returnValue->value.boolean = left->value.integer < right->value.integer;
break;
case bGREATERTHAN:
returnValue->value.boolean = left->value.integer > right->value.integer;
break;
case bEQUALTO:
returnValue->value.boolean = left->value.integer == right->value.integer;
break;
default:
// this is a bad problem
error("Unknown boolean operation");
free(left);
free(right);
free(returnValue);
return NIL;
}
free(left);
free(right);
return returnValue;
case sINT:
returnValue = malloc(sizeof(Element));
returnValue->type = tINT;
returnValue->value = stmt->value;
return returnValue;
case sVAR:
// make sure variable is in state, if it isn't that's a bit of a problem
if (!exists(state->h, stmt->name)) {
error("Variable doesn't exist");
return NIL;
} else {
// stmt->value might not be correct, obtain value from state
k = kh_get(32, state->h, stmt->name);
returnValue = malloc(sizeof(Element));
memcpy(returnValue, kh_val(state->h, k), sizeof(Element));
return returnValue;
}
case sARITH:
// TODO: handle real numbers
left = evaluate(stmt->children[0], state);
right = evaluate(stmt->children[1], state);
returnValue = malloc(sizeof(Element));
returnValue->type = tINT;
switch(stmt->op.arithop) {
case aPLUS:
returnValue->value.integer = left->value.integer + right->value.integer;
break;
case aSUB:
returnValue->value.integer = left->value.integer - right->value.integer;
break;
case aDIV:
returnValue->value.integer = left->value.integer / right->value.integer;
break;
case aMULT:
returnValue->value.integer = left->value.integer * right->value.integer;
break;
default:
// whoops
error("Unknown arithmetic operation");
free(left);
free(right);
free(returnValue);
return NIL;
}
free(left);
free(right);
return returnValue;
default:
// if you reach here you have a bad problem
// and you will not evaluate a statement today (or maybe ever)
error("Fatal: unknown statement type");
return NIL;
}
}
ParseNode *buildST(const char *input) {
ParseNode *stmt;
yyscan_t scanner;
YY_BUFFER_STATE state;
if (yylex_init(&scanner)) {
// couldn't initialize
return NULL;
}
state = yy_scan_string(input, scanner);
if (yyparse(&stmt, scanner)) {
// error parsing
return NULL;
}
yy_delete_buffer(state, scanner);
yylex_destroy(scanner);
return stmt;
}
Element *evaluateLine(char *line, State *state) {
ParseNode *stmt = buildST(line);
Element *val = NULL;
if (stmt == NULL) {
error("Could not build syntax tree.");
return NULL;
}
/* Evaluate the syntax tree */
val = evaluate(stmt, state);
deleteStatement(stmt);
return val;
}
void freeNil() {
if (_nil != NULL)
free(_nil);
}