diff --git a/calculate_pi.script b/calculate_pi.script
index d489ae8..d0f4c04 100644
--- a/calculate_pi.script
+++ b/calculate_pi.script
@@ -3,7 +3,7 @@ k := 0
 
 iterations := 100
 
-while k - iterations {
+while k < iterations {
 	k_f := float(k)
 	sum = sum + 1.0 / pow(16.0, k_f) *
 		(4.0 / (8.0 * k_f + 1.0) -
diff --git a/ir.c b/ir.c
index 0f58aa7..4147220 100644
--- a/ir.c
+++ b/ir.c
@@ -10,6 +10,10 @@ const char *irinstr_str[IRInstrEnumSize] = {
 	[IRSub] = "sub",
 	[IRMul] = "mul",
 	[IRDiv] = "div",
+	[IREq]  = "eq",
+	[IRLt]  = "lt",
+	[IRLe]  = "le",
+	[IRNot] = "not",
 	[IRJmp] = "jmp",
 	[IRJnz] = "jnz",
 	[IRCallInternal] = "calli",
@@ -77,6 +81,9 @@ static void print_val(const Value *v) {
 		case TypeInt:
 			printf("%zd", v->Int);
 			break;
+		case TypeBool:
+			printf("%s", v->Bool ? "true" : "false");
+			break;
 		default:
 			printf("(unknown type)");
 			break;
@@ -105,6 +112,9 @@ void print_ir(IRToks *v, const BuiltinFunc *builtin_funcs) {
 			case IRSub:
 			case IRDiv:
 			case IRMul:
+			case IREq:
+			case IRLt:
+			case IRLe:
 				printf(" %%%zx ", v->toks[i].Binary.addr);
 				print_irparam(&v->toks[i].Binary.lhs);
 				printf(" ");
diff --git a/ir.h b/ir.h
index fae539e..1ab87d2 100644
--- a/ir.h
+++ b/ir.h
@@ -18,6 +18,10 @@ enum IRInstr {
 	IRSub,
 	IRMul,
 	IRDiv,
+	IREq,
+	IRLt,
+	IRLe,
+	IRNot,
 	IRJmp,
 	IRJnz,
 	IRCallInternal,
diff --git a/lex.c b/lex.c
index deee6c0..68aa3a5 100644
--- a/lex.c
+++ b/lex.c
@@ -58,6 +58,10 @@ TokList lex(const char *s) {
 				emit(&toks, &pos, (Tok){ .kind = TokElse });
 			else if (streq_0_n("while", start, i))
 				emit(&toks, &pos, (Tok){ .kind = TokWhile });
+			else if (streq_0_n("true", start, i))
+				emit(&toks, &pos, (Tok){ .kind = TokVal, .Val = { .type = { .kind = TypeBool, }, .Bool = true, }, });
+			else if (streq_0_n("false", start, i))
+				emit(&toks, &pos, (Tok){ .kind = TokVal, .Val = { .type = { .kind = TypeBool, }, .Bool = false, }, });
 			else {
 				emit(&toks, &pos, (Tok){
 						.kind = TokIdent,
@@ -162,15 +166,39 @@ TokList lex(const char *s) {
 				break;
 			case ':':
 				consume(&pos, *(s++));
-				if (s[0] == '=') {
+				if (s[0] == '=')
 					emit(&toks, &pos, (Tok){ .kind = TokDeclare });
-				} else {
+				else {
 					set_err("Expected ':='");
 					return toks;
 				}
 				break;
 			case '=':
-				emit(&toks, &pos, (Tok){ .kind = TokAssign });
+				consume(&pos, *(s++));
+				if (s[0] == '=')
+					emit(&toks, &pos, (Tok){ .kind = TokOp, .Op = OpEq });
+				else {
+					emit(&toks, &pos, (Tok){ .kind = TokAssign });
+					continue;
+				}
+				break;
+			case '<':
+				consume(&pos, *(s++));
+				if (s[0] == '=')
+					emit(&toks, &pos, (Tok){ .kind = TokOp, .Op = OpLe });
+				else {
+					emit(&toks, &pos, (Tok){ .kind = TokOp, .Op = OpLt });
+					continue;
+				}
+				break;
+			case '>':
+				consume(&pos, *(s++));
+				if (s[0] == '=')
+					emit(&toks, &pos, (Tok){ .kind = TokOp, .Op = OpGe });
+				else {
+					emit(&toks, &pos, (Tok){ .kind = TokOp, .Op = OpGt });
+					continue;
+				}
 				break;
 			case '{':
 			case '}':
@@ -180,6 +208,7 @@ TokList lex(const char *s) {
 			case '+':
 			case '-':
 			case '*':
+			case '!':
 				emit(&toks, &pos, (Tok){
 						.kind = TokOp,
 						.Op = s[0],
diff --git a/main.c b/main.c
index f202cca..9aa265a 100644
--- a/main.c
+++ b/main.c
@@ -35,9 +35,10 @@ static void die(const char *fmt, ...) {
 
 static Value fn_print(Value *args) {
 	switch (args[0].type.kind) {
-		case TypeVoid:  printf("(void)\n");            break;
-		case TypeFloat: printf("%f\n", args[0].Float); break;
-		case TypeInt:   printf("%zd\n", args[0].Int);  break;
+		case TypeVoid:  printf("(void)\n");                              break;
+		case TypeFloat: printf("%f\n", args[0].Float);                   break;
+		case TypeInt:   printf("%zd\n", args[0].Int);                    break;
+		case TypeBool:  printf("%s\n", args[0].Bool ? "true" : "false"); break;
 		default:
 			ASSERT_UNREACHED();
 	}
diff --git a/parse.c b/parse.c
index 0bb68d8..7f6b31d 100644
--- a/parse.c
+++ b/parse.c
@@ -46,12 +46,16 @@ static void set_irtok_dest_addr(IRTok *t, size_t addr) {
 	switch (t->instr) {
 		case IRSet:
 		case IRNeg:
+		case IRNot:
 			t->Unary.addr = addr;
 			break;
 		case IRAdd:
 		case IRSub:
 		case IRMul:
 		case IRDiv:
+		case IREq:
+		case IRLt:
+		case IRLe:
 			t->Binary.addr = addr;
 			break;
 		case IRCallInternal:
@@ -172,11 +176,19 @@ static ExprRet expr(IRToks *out_ir, TokList *toks, Map *funcs, Scope *parent_sc,
 	Scope sc = make_scope(parent_sc, false);
 
 	for (;;) {
-		/* Prepare to collapse negative factor. */
-		bool negate = false;
-		if (t->tok.kind == TokOp && t->tok.Op == OpSub) {
-			t = t->next;
-			negate = true;
+		/* Prepare to collapse unary operation. */
+		bool perform_unary = false;
+		IRInstr unary_op;
+		if (t->tok.kind == TokOp) {
+			if (t->tok.Op == OpSub) {
+				t = t->next;
+				perform_unary = true;
+				unary_op = IRNeg;
+			} else if (t->tok.Op == OpNot) {
+				t = t->next;
+				perform_unary = true;
+				unary_op = IRNot;
+			}
 		}
 
 		/* Delete newline if we're definitely expecting an operand. */
@@ -312,28 +324,28 @@ static ExprRet expr(IRToks *out_ir, TokList *toks, Map *funcs, Scope *parent_sc,
 			}
 		}
 
-		/* Collapse negative factor. */
-		if (negate) {
-			Tok *v = &t->tok; /* what we want to negate */
+		/* Collapse unary operation. */
+		if (perform_unary) {
+			Tok *v = &t->tok; /* what we want to perform the operation on */
 			t = t->prev; /* go back to the '-' sign */
 			toklist_del(toks, t->next, t->next); /* again, just removing the reference */
 
 			bool is_last_operation = t == start && t->next->tok.kind == TokOp && op_prec[t->next->tok.Op] == PREC_DELIM;
 
 			if (v->kind == TokVal) {
-				/* immediately negate value */
+				/* immediately perform operation */
 				t->tok.kind = TokVal;
-				t->tok.Val = eval_unary(IRNeg, &v->Val);
+				TRY_RET(t->tok.Val = eval_unary(unary_op, &v->Val), (ExprRet){0});
 			} else {
 				size_t res_addr = is_last_operation ? 0 : sc.mem_addr++;
 
-				/* Instruction to negate. */
+				/* unary IR instruction */
 				IRParam v_irparam;
 				TRY_RET(v_irparam = tok_to_irparam(&sc, v), (ExprRet){0});
 				IRTok ir = {
 					.ln = t->tok.ln,
 					.col = t->tok.col,
-					.instr = IRNeg,
+					.instr = unary_op,
 					.Unary = {
 						.addr = res_addr,
 						.val = v_irparam,
@@ -421,12 +433,19 @@ static ExprRet expr(IRToks *out_ir, TokList *toks, Map *funcs, Scope *parent_sc,
 			 * because we're still using their values later on) */
 			toklist_del(toks, t->next, t->next->next);
 
+			bool swap_operands = false;
+
 			IRInstr instr;
 			switch (l_op->Op) {
 				case OpAdd: instr = IRAdd; break;
 				case OpSub: instr = IRSub; break;
 				case OpMul: instr = IRMul; break;
 				case OpDiv: instr = IRDiv; break;
+				case OpEq:  instr = IREq;  break;
+				case OpLt:  instr = IRLt;  break;
+				case OpLe:  instr = IRLe;  break;
+				case OpGt:  instr = IRLt; swap_operands = true; break;
+				case OpGe:  instr = IRLe; swap_operands = true; break;
 				default:
 					mark_err(l_op);
 					set_err("Unknown operation: '%s'", op_str[l_op->Op]);
@@ -435,8 +454,10 @@ static ExprRet expr(IRToks *out_ir, TokList *toks, Map *funcs, Scope *parent_sc,
 
 			if (lhs->kind == TokVal && rhs->kind == TokVal) {
 				/* evaluate the constant expression immediately */
+				Value *lhs_val = swap_operands ? &rhs->Val : &lhs->Val;
+				Value *rhs_val = swap_operands ? &lhs->Val : &rhs->Val;
 				lhs->kind = TokVal;
-				TRY_RET(lhs->Val = eval_binary(instr, &lhs->Val, &rhs->Val), (ExprRet){0});
+				TRY_RET(lhs->Val = eval_binary(instr, lhs_val, rhs_val), (ExprRet){0});
 			} else {
 				bool is_last_operation = t == start && r_op_prec == PREC_DELIM;
 
@@ -452,8 +473,8 @@ static ExprRet expr(IRToks *out_ir, TokList *toks, Map *funcs, Scope *parent_sc,
 					.instr = instr,
 					.Binary = {
 						.addr = res_addr,
-						.lhs = lhs_irparam,
-						.rhs = rhs_irparam,
+						.lhs = swap_operands ? rhs_irparam : lhs_irparam,
+						.rhs = swap_operands ? lhs_irparam : rhs_irparam,
 					},
 				};
 				
diff --git a/runtime.c b/runtime.c
index 2f50f61..0c18a45 100644
--- a/runtime.c
+++ b/runtime.c
@@ -39,6 +39,32 @@ Value eval_binary(IRInstr instr, const Value *lhs, const Value *rhs) {
 				return (Value){0};
 			}
 		}
+		case IREq:
+		case IRLt:
+		case IRLe:
+			bool res;
+			if (lhs->type.kind == TypeInt && rhs->type.kind == TypeInt) {
+				switch (instr) {
+					case IREq: res = lhs->Int == rhs->Int; break;
+					case IRLt: res = lhs->Int <  rhs->Int; break;
+					case IRLe: res = lhs->Int <= rhs->Int; break;
+					default: ASSERT_UNREACHED();
+				};
+			} else if (lhs->type.kind == TypeFloat && rhs->type.kind == TypeFloat) {
+				switch (instr) {
+					case IREq: res = lhs->Float == rhs->Float; break;
+					case IRLt: res = lhs->Float <  rhs->Float; break;
+					case IRLe: res = lhs->Float <= rhs->Float; break;
+					default: ASSERT_UNREACHED();
+				};
+			} else {
+				set_err("Unsupported types for operation '%s'", irinstr_str[instr]);
+				return (Value){0};
+			}
+			return (Value){
+				.type.kind = TypeBool,
+				.Bool = res,
+			};
 		default:
 			ASSERT_UNREACHED();
 	}
@@ -55,7 +81,14 @@ Value eval_unary(IRInstr instr, const Value *v) {
 			else if (v->type.kind == TypeFloat)
 				return (Value){ .type.kind = TypeFloat, .Float = -v->Float };
 			else {
-				set_err("Unsupported types for operation '%s'", irinstr_str[instr]);
+				set_err("Unsupported type for operation '%s'", irinstr_str[instr]);
+				return (Value){0};
+			}
+		case IRNot:
+			if (v->type.kind == TypeBool) {
+				return (Value){ .type.kind = TypeBool, .Bool = !v->Bool };
+			} else {
+				set_err("Unsupported type for operation '%s'", irinstr_str[instr]);
 				return (Value){0};
 			}
 		default:
@@ -67,6 +100,7 @@ bool is_nonzero(const Value *v) {
 	switch (v->type.kind) {
 		case TypeInt:   return v->Int   != 0;
 		case TypeFloat: return v->Float != 0.0;
+		case TypeBool:  return v->Bool;
 		default: ASSERT_UNREACHED();
 	}
 }
@@ -75,8 +109,9 @@ Value zero_val(Type ty) {
 	Value ret;
 	ret.type = ty;
 	switch (ty.kind) {
-		case TypeInt:   ret.Int   = 0;   break;
-		case TypeFloat: ret.Float = 0.0; break;
+		case TypeInt:   ret.Int   = 0;     break;
+		case TypeFloat: ret.Float = 0.0;   break;
+		case TypeBool:  ret.Bool  = false; break;
 		default: ASSERT_UNREACHED();
 	}
 	return ret;
diff --git a/tok.c b/tok.c
index 6756fe4..4d324e2 100644
--- a/tok.c
+++ b/tok.c
@@ -11,10 +11,15 @@ int8_t op_prec[OperatorEnumSize] = {
 	[OpLCurl]  = PREC_DELIM,
 	[OpRParen] = PREC_DELIM,
 	[OpComma]  = PREC_DELIM,
-	[OpAdd]    = 0,
-	[OpSub]    = 0,
-	[OpMul]    = 1,
-	[OpDiv]    = 1,
+	[OpEq]     = 0,
+	[OpLt]     = 0,
+	[OpGt]     = 0,
+	[OpLe]     = 0,
+	[OpGe]     = 0,
+	[OpAdd]    = 1,
+	[OpSub]    = 1,
+	[OpMul]    = 2,
+	[OpDiv]    = 2,
 };
 
 const char *op_str[OperatorEnumSize] = {
@@ -27,8 +32,14 @@ const char *op_str[OperatorEnumSize] = {
 	[OpSub]    = "-",
 	[OpMul]    = "*",
 	[OpDiv]    = "/",
+	[OpNot]    = "!",
 	[OpNewLn]  = "\\n",
 	[OpEOF]    = "EOF",
+	[OpEq]     = "==",
+	[OpLt]     = "<",
+	[OpGt]     = ">",
+	[OpLe]     = "<=",
+	[OpGe]     = ">=",
 };
 
 const char *tok_str[TokKindEnumSize] = {
@@ -101,6 +112,9 @@ void print_toks(TokList *l) {
 					case TypeInt:
 						printf(": " C_ICYAN "%zd" C_RESET, i->tok.Val.Int);
 						break;
+					case TypeBool:
+						printf(": " C_ICYAN "%s" C_RESET, i->tok.Val.Bool ? "true" : "false");
+						break;
 					default:
 						printf(" " C_ICYAN "(unknown type)" C_RESET);
 						break;
diff --git a/tok.h b/tok.h
index 54ec65d..3a8e1f3 100644
--- a/tok.h
+++ b/tok.h
@@ -11,6 +11,7 @@ typedef struct Type {
 		TypeVoid = 0,
 		TypeFloat,
 		TypeInt,
+		TypeBool,
 	} kind;
 
 	/*union {
@@ -23,6 +24,7 @@ typedef struct Value {
 	union {
 		double Float;
 		ssize_t Int;
+		bool Bool;
 	};
 } Value;
 
@@ -36,7 +38,13 @@ enum Operator {
 	OpSub    = '-',
 	OpMul    = '*',
 	OpDiv    = '/',
+	OpNot    = '!',
 	OpBeginNonchars = 256,
+	OpEq,
+	OpLt,
+	OpGt,
+	OpLe,
+	OpGe,
 	OpNewLn,
 	OpEOF,
 	OperatorEnumSize,
diff --git a/vm.c b/vm.c
index 39eb2d6..d998585 100644
--- a/vm.c
+++ b/vm.c
@@ -55,6 +55,7 @@ void run(const IRToks *ir, const BuiltinFunc *builtin_funcs) {
 		switch (instr->instr) {
 			case IRSet:
 			case IRNeg:
+			case IRNot:
 				stack_fit(&s, instr->Unary.addr);
 				TRY_ELSE(s.mem[instr->Unary.addr] = eval_unary(instr->instr, irparam_to_val(&s, &instr->Unary.val)),
 					{free(fn_args); stack_term(&s);});
@@ -63,6 +64,9 @@ void run(const IRToks *ir, const BuiltinFunc *builtin_funcs) {
 			case IRSub:
 			case IRDiv:
 			case IRMul:
+			case IREq:
+			case IRLt:
+			case IRLe:
 				stack_fit(&s, instr->Binary.addr);
 				TRY_ELSE(s.mem[instr->Binary.addr] = eval_binary(instr->instr,
 					irparam_to_val(&s, &instr->Binary.lhs),