The Department of Computer Science & Engineering
 STUART C. SHAPIRO: CSE 305

# Expressions and Assignment Statements

Precedence
Determines the order of operation in an expression such as ```w - x / y - z``` or `w / x - y / z`. Operators with higher precedence are done first. Parentheses are used to override precedence. Languages tend to be similar in their operator precedence order.

Associativity
Determines the order of operation between operators of the same precedence, such as `x - y - z` or `x / y / z`. Most operators in most languages are left associative, except that exponentiation (when included) is usually right associative. Parentheses are, again, used to override associativity.

For example, Python's subtraction operator is left-associative, and its exponentiation is right-associative:

```>>> 100-50-25
25
>>> (100-50)-25
25
>>> 100-(50-25)
75

>>> 2**2**2**2
65536
>>> 2**(2**(2**2))
65536
>>> ((2**2)**2)**2
256
```

A mathematical operator, •, is associative when ((x • y) • z) = (x • (y • z)), so that the order of evaluation does not matter. Addition and multiplication are mathematically associative, but may not be associative computationally. For example,

```
bsh % print(3e17+4.+4.+4.+4.+4.+4.+4.+4.+4.+4.+4.);
3.0E17

bsh % print(3e17+(4.+4.+4.+4.+4.+4.+4.+4.+4.+4.+4.));
3.0000000000000006E17
```
So when adding a series of floating point numbers, it is better to add them starting with the smallest terms than starting with the largest terms.

Operand Evaluation Order
The issue of operand evaluation order is:
in an expression such as ```<expression>1 • <expression>2```,
is `<expression>1` or `<expression>2` evaluated first?
It will not matter unless one of the `expression`s has a side effect.

A side effect occurs when the evaluation of an expression causes a change to some variable, rather than only producing a value. Here's an example in Java:

```
public class OperandOrder {
public static int x;

public static int f(int y) {
x++;
return y;
}

public static void main (String[] args) {
int result;
x = 3;
result = x + f(5);
System.out.println("First evaluation = " + result);

x = 3;
result = f(5) + x;
System.out.println("Second evaluation = " + result);
} // end of main ()

}// OperandOrder

------------------------------------------------
<timberlake:Tests:1:102> javac OperandOrder.java

<timberlake:Tests:1:103> java OperandOrder
First evaluation = 8
Second evaluation = 9
```
"The Java programming language guarantees that the operands of operators appear to be evaluated in a specific evaluation order, namely, from left to right." [Java Language Specification Second Edition, Section 15.7]

And, here's C:

```
#include <stdio.h>

int x;

int f(int y) {
x++;
return y;
}

int g(int y) {
return y;
}

int main() {
int result;
x = 3;
result = x + f(5);
printf("First evaluation = %3d\n", result);

x = 3;
result = f(5) + x;
printf("Second evaluation = %3d\n", result);

x = 3;
result = g(x) + f(5);
printf("Third evaluation = %3d\n", result);

x = 3;
result = f(5) + g(x);
printf("Fourth evaluation = %3d\n", result);

return 0;
}
------------------------------------------------
<timberlake:Programs:2:180> gcc -Wall -o operandOrder operandOrder.c
<timberlake:Programs:2:180> ./operandOrder
First evaluation =   9
Second evaluation =   9
Third evaluation =   8
Fourth evaluation =   9
```
This C compiler seems to evaluate function calls before simple variables regardless of their order.

"Except as specified later (for the function-call (), &&, ||, ?:, and comma operators), the order of evaluation of subexpressions and the order in which side effects take place are both unspecified." [ISO C Standard, Sect. 6.5[#3]]

Optimizing compilers may change the order of operand evaluation. They sometimes allow the programmer to specify that a certain section of code should not be optimized.

An overloaded operator is one that compiles into different procedures depending on the types of its operands, such as `+` compiling into one prodecure for `int`s, another for `float`s, and another for `String`s.

C++ and some other languages allow the programmer to supply additional overloadings to most or all of its operators.

Type Conversions
A widening conversion converts a value from type A to type B where no two type A values convert to the same type B value (at least within reasonable bounds of range and precision), and there are type B values that no type A value converts to. An example is conversion from `int` to `double`.

A narrowing conversion converts a value from type A to type B where multiple values of type A convert to the same value of type B (even within reasonable bounds of range and precision). An example is conversion from `double` to `int`.

```
bsh % int i;
bsh % double x;

bsh % i = 3;
bsh % x = i;
bsh % print(x);
3.0

bsh % x = 3.5;
bsh % i = (int)x;
bsh % print(i);
3
```
However, here's an example where even widening doesn't work because of loss of precision:
```
bsh % float y;

bsh % y = 123456792;
bsh % print(y);
1.23456792E8

bsh % y = 123456793;
bsh % print(y);
1.23456792E8
```
Usually, if the operands of one operator are of different types, the value of one is automatically converted (coerced) to the type of the other as long as that is a widening conversion, but a narrowing conversion must be explicitly specified by a cast.

For example, in Python:

```>>> 9.7
9.6999999999999993
>>> type(9.7)
<type 'float'>
>>> type(2)
<type 'int'>
>>> 9.7 + 2
11.699999999999999
>>> type(9.7+2)
<type 'float'>
>>> int(9.7)
9
>>> type(int(9.7) + 2)
<type 'int'>
```
This example also shows an especially obvious example of loss of precision and representation errors when dealing with floating point numbers: Python converts the literal 9.7 to 9.6999999999999993!

Relational and Boolean Expressions
Relational expressions test or compare values of non-Boolean types, and evaluate to Boolean types. A simple example of a relational expression is `x == y`. Note, however, that two floating-point values, computed differently, are seldom equal.

Boolean expressions apply a Boolean operator to Boolean values. An example is `i < max && a[i] == x`. Usually, Boolean operators have lower precedence than relational and arithmetic operators. However, using parentheses is often a good idea, for example, `(i < max) && (a[i] == x)`.

A standard warning given to novice programmers is that ```i < j < k``` is not correct;
it must be written ```(i < j) && (j < k)```. Since C uses `0` and `1` for Boolean values, one can get:

```
#include <stdio.h>

int main() {
int i=5, j=7, k=3;

if (i < j < k) {
printf("It's true that %d < %d < %d\n", i, j, k);
}
return 0;
}

-----------------------------------------------------
<timberlake:Test:1:43> gcc -Wall -o boolTest boolTest.c
boolTest.c: In function รข:
boolTest.c:6: warning: comparisons like X<=Y<=Z do not have their mathematical meaning
./boolTest
It's true that 5 < 7 < 3

```
```#include <stdio.h>

int main() {
int i=5, j=7, k=3;

if (i < j < k) {
printf("%d < %d : %d\n", i, j, i < j);
printf("%d < %d : %d\n", j,k, j < k);
}
return 0;
}
-----------------------------------------------------
bash-3.2\$ gcc -Wall -o boolTest2 boolTest2.c
boolTest2.c: In function 'main':
boolTest2.c:6: warning: comparisons like X<=Y<=Z do not have their mathematical meaning
bash-3.2\$ ./boolTest2
5 < 7 : 1
7 < 3 : 0
```

Python, however, allows these expressions:

```
Python 2.6.4 (r264:75706, Dec 21 2009, 12:48:32)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)] on linux2

>>> i = 5
>>> j = 7
>>> k = 3

>>> i<j<k
False

>>> k<i<j
True
>>> ```

Trust the Boolean type! I have often seen code like

```
if (<test>) {return true;}
else {return false;}
```
```
return <test>;
```
Short-circuit evaluation is the evaluation of an expression without evaluating all its subexpressions. The text has some excellent examples of when short-circuit evaluation prevents run-time errors.

Conditional Expressions
The imperative programming style is to use imperative statements: "Do this." For example, the C function to compute absolute value uses the imperative statement `return x` enclosed in a conditional statement:
```
#include <stdio.h>

int absval(int x)
{
if (x >= 0) {
return x;
}
else {
return -x;
}
}

int main() {
printf("The absolute value of %3d is %3d\n", 5, absval(5));
printf("The absolute value of %3d is %3d\n", -5, absval(-5));

return 0;
}
-------------------------------------------------------------------
<timberlake:Test:1:34> gcc -Wall -o absval absval.c
<timberlake:Test:1:35> ./absval
The absolute value of   5 is   5
The absolute value of  -5 is   5

```
The declarative (non-imperative) style doesn't say "Do this," but "this is that," which requires a conditional expression. For example, in Haskell:
```
<timberlake:Test:1:37> ghci
GHCi, version 6.12.1: http://www.haskell.org/ghc/  :? for help

Prelude> let absval x = if x>=0 then x else -x

Prelude> absval 5
5

Prelude> absval (-5)
5
```
Declarative style, rather than declarative programming language, because some "imperative languages" include the conditional expression also. Again, in C:
```
#include

int absval(int x)
{
return x >= 0 ? x : -x;
}

int main() {
printf("The absolute value of %3d is %3d\n", 5, absval(5));
printf("The absolute value of %3d is %3d\n", -5, absval(-5));

return 0;
}
-----------------------------------------------------------------
<timberlake:Test:1:38> gcc -Wall -o absval2 absval2.c
<timberlake:Test:1:39> ./absval2
The absolute value of   5 is   5
The absolute value of  -5 is   5
<timberlake:Test:1:40>
```
The conditional expression uses the trinary operator
```
<condition> ? <then-expression> : <else-expression>
```
This operator exists in all the C-based languages.

Lazy Evaluation
In languages that use strict (sometimes called "eager") evaluation, including most of the languages we're using this semester, expressions are evaluated well before their values are needed. In many languages an expression on the right hand side of an assignment statement is evaluated when the expression is bound to the variable (on the LHS). Under strict evaluation an expression passed as an argument to a function is evaluated before the function call occurs, and its value is used as the actual argument. Most programming languages, including those in the C family, use strict evaluation by default.

Haskell uses lazy evaluation. Under lazy evaluation, expressions are evaluated only when their values are needed. Evaluation of an expression is delayed until its value is required, e.g. in the course of evaluating another expression. In Haskell, when an expression is passed as the actual argument to a function, it is not evaluated unless and when its value is required somewhere in the body of the function.

```
Prelude> let x = [1..]
1
2
3
4
Prelude> tail(x)
[2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290,291,292,293,294,295,296,297,298,299,300,301,302,303,304,305,306,307,308,309,310,311,312,313,314,315,316,317,318,319,320,321,322,323,324,325,326,327,328,329,330,331,332,333,334,335,336,337,338,339,340,341,342,343,344,345,346,347,348,349,350,351,352,353,354,355,356,357,358,359,360,361,362,363,364,365,366,367,368,369,370,371,372,373,374,375,376,377,378,379,380,381,382,383,384,385,386,387,388,389,390,391,392,393,394,395,396,397,398,399,400,401,402,403,404,405,406,407,408,409,410,411,412,413,414,415,416,417,418,419,420,421,422,423,424,425,426,427,428,429,430,431,432,433,434,435,436,437,438,439,440,441,442,443,444,445,446,447,448,449,450,451,452,453,454,455,456,457,458,459,460,461,462,463,464,465,466,467,468,469,470,471,472,473,474,475,476,477,478,479,480,481,482,483,484,485,486,487,488,489,490,491,492,493,494,495,496,497,498,499,500,501,502,503,504,505,506,507,508,509,510,511,512,513,514,515,516,517,518,519,520,521,522,523,524,525,526,527,528,529,530,531,532,533,534,535,536,537,538,539,540,541,542,543,544,545,546,547,548,549,550,551,552,553,554,555,556,557,558,559,560,561,562,563,564,565,566,567,568,569,570,571,572,573,574,575,576,577,578,579,580,581,582,583,584,585,586,587,588,589,590,591,592,593,594,595,596,597,598,599,600,601,602,603,604,605,606,607,608,609,610,611,612,613,614,615,616,617,618,619,620,621,622,623,624,625,626,627,628,629,630,631,632,633,634,635,636,637,638,639,640,641,642,643,644,645,646,647,648,649,650,651,652,653,654,655,656,657,658,659,660,661,662,663,664,665,666,667,668,669,670,671,672,673,674,675,676,677,678,679,680,681,682,683,684,685,686,687,688,689,690,691,692,693,694,695,696,697,698,699,700,701,702,703,704,705,706,707,708,709,710,711,712,713,714,715,716,717,718,719,720,721,722,723,724,725,726,727,728,729,730,731,732,733,734,735,736,737,738,739,740,741,742,743,744,745,746,747,748,749,750,751,752,753,754,755,756,757,758,759,760,761,762,763,764,765,766,767,768,769,770,771,772,773,774,775,776,777,778,779,780,781,782,783,784,785,786,787,788,789,790,791,792,793,794,795,796,797,798,799,800,801,802,803,804,805,806,807,808,809,810,811,812,813,814,815,816,817,818,819,820,821,822,823,824,825,826,827,828,829,830,831,832,833,834,835,836,837,838,839,840,841,842,843,844,845,846,847,848,849,850,851,852,853,854,855,856,857,858,859,860,861,862,863,864,865,866,867,868,869,870,871,872,873,874,875,876,877,878,879,880,881,882,883,884,885,886,887,888,889,890,891,892,893,894,895,896,897,898,899,900,901,902,903,904,905,906,907,908,909,910,911,912,913,914,915,916,917,918,919,920,921,922,923,924,925,926,927,928,929,930,931,932,933,934,935,936,937,938,939,940,941,942,943,944,945,946,947,948,949,950,951,952,953,954,955,956,957,958,959,960,961,962,963,964,965,966,967,968,969,970,971,972,973,974,975,976,977,978,979,980,981,982,983,984,985,986,987,988,989,990,991,992,993,994,995,996,997,998,999,1000,1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1011,1012,1013,1014,1015,1016,1017,1018,1019,1020,1021,1022,1023,1024,1025,1026,1027,1028,1029,1030,1031,1032,1033,1034,1035,1036,1037,1038,1039,1040,1041,1042,1043,1044,1045,1046,1047,1048,1049,1050,1051,1052,1053,1054,1055,1056,1057,1058,1059,1060,1061,1062,1063,1064,1065,1066,1067,1068,1069,1070,1071,1072,1073,1074,1075,1076,1077,1078,1079,1080,1081,1082,1083,1084,1085,1086,1087,1088,1089,1090,1091,1092,1093,1094,1095,1096,1097,1098,1099,1100,1101,1102,1103,1104,1105,1106,1107,1108,1109,1110,1111,1112,1113,1114,1115,1116,1117,1118,1119,1120,1121,1122,1123,1124,1125,1126,1127,1128,1129,1130,1131,1132,1133,1134,1135,1136,1137,1138,1139,1140,1141,1142,1143,1144,1145,1146,1147,1148,1149,1150,1151,1152,1153,1154,1155,1156,1157,1158,1159,1160,1161,1162,1163,1164,1165,1166,1167,1168,1169,1170,1171,1172,1173,1174,1175,1176,1177,1178,1179,1180,1181,1182,1183,1184,1185,1186,1187,1188,1189,1190,1191,1192,1193,1194,1195,1196,1197,1198,1199,1200,1201,1202,1203,1204,1205,1206,1207,1208,1209,1210,1211,1212,1213,1214,1215,1216,1217,1218,1219,1220,1221,1222,1223,1224,1225,1226,1227,1228,1229,1230,1231,1232,1233,1234,1235,1236,1237,1238,1239,1240,1241,1242,1243,1244,1245,1246,1247,1248,1249,1250,1251,1252,1253,1254,1255,1256,1257,1258,1259,1260,1261,1262,1263,1264,1265,1266,1267,1268,1269,1270,1271,1272,1273,1274,1275,1276,1277,1278,1279,1280,1281,1282,1283,1284,1285,1286,1287,1288,1289,1290,1291,1292,1293,1294,1295,1296,1297,1298,1299,1300,1301,1302,1303,1304,1305,1306,1307,1308,1309,1310,1311,1312,1313,1314,1315,1316,1317,1318,1319,1320,1321,1322,1323,1324,1325,1326,1327,1328,1329,1330,1331,1332,1333,1334,1335,1336,1337,1338,1339,1340,1341,1342,1343,1344,1345,1346,1347,1348,1349,1350,1351,1352,1353,1354,1355,1356,1357,1358,1359,1360,1361,1362,1363,1364,1365,1366,1367,1368,1369,1370,1371,1372,1373,1374,1375,1376,1377,1378,1379,1380,1381,1382,1383,1384,1385,1386,1387,1388,1389,1390,1391,1392,1393,1394,1395,1396,1397,1398,1399,1400,1401,1402,1403,1404,1405,1406,1407,1408,1409,1410,1411,1412,1413,1414,1415,1416,1417,1418,1419,1420,1421,1422,1423,1424,1425,1426,1427,1428,1429,1430,1431,1432,1433,1434,1435,1436,1437,1438,1439,1440,1441,1442,1443,1444,1445,1446,1447,1448,1449,1450,1451,1452,1453,1454,1455,1456,1457,1458,1459,1460,1461,1462,1463,1464,1465,1466,1467,1468,1469,1470,1471,1472,1473,1474,1475,1476,1477,1478,1479,1480,1481,1482,1483,1484,1485,1486,1487,1488,1489,1490,1491,1492,1493,1494,1495,1496,1497,1498,1499,1500,1501,1502,1503,1504,1505,1506,1507,1508,1509,1510,1511,1512,1513,1514,1515,1516,1517,1518,1519,1520,1521,1522,1523,1524,1525,1526,1527,1528,1529,1530,1531,1532,1533,1534,1535,1536,1537,1538,1539,1540,1541,1542,1543,1544,1545,1546,1547,1548,1549,1550,1551,1552,1553,1554,1555,1556,1557,1558,1559,1560,1561,1562,1563,1564,1565,1566,1567,1568,1569,1570,1571,1572,1573,1574,1575,1576,1577,1578,1579,1580,1581,1582,1583,1584,1585,1586,1587,1588,1589,1590,1591,1592,1593,1594,1595,1596,1597,1598,1599,1600,1601,1602,1603,1604,1605,1606,1607,1608,1609,1610,1611,1612,1613,1614,1615,1616,1617,1618,1619,1620,1621,1622,1623,1624,1625,1626,1627,1628,1629,1630,1631,1632,1633,1634,1635,1636,1637,1638,1639,1640,1641,1642,1643,1644,1645,1646,1647,1648,1649,1650,1651,1652,1653,1654,1655,1656,1657,1658,1659,1660,1661,1662,1663,1664,1665,1666,1667,1668,1669,1670,1671,1672,1673,1674,1675,1676,1677,1678,1679,1680,1681,1682,1683,1684,1685,1686,1687,1688,1689,1690,1691,1692,1693,1694,1695,1696,1697,1698,1699,1700,1701,1702,1703,1704,1705,1706,1707,1708,1709,1710,1711,1712,1713,1714,1715,1716,1717,1718,1719,1720,1721,1722,1723,1724,1725,1726,1727,1728,1729,1730,1731,1732,1733,1734,1735,1736,1737,1738,1739,1740,1741,1742,1743,1744,1745,1746,1747,1748,1749,1750,1751,1752,1753,1754,1755,1756,1757,1758,1759,1760,1761,1762,1763,1764,1765,1766,1767,1768,1769,1770,1771,1772,1773,1774,1775,1776,1777,1778,1779,1780,1781,1782,1783,1784,1785,1786,1787,1788,1789,1790,1791,1792,1793,1794,1795,1796,1797,1798,1799,1800,1801,1802,1803,1804,1805,1806,1807,1808,1809,1810,1811,1812,1813,1814,1815,1816,1817,1818,1819,1820,1821,1822,1823,1824,1825,1826,1827,1828,1829,1830,1831,1832,1833,1834,1835,1836,1837,1838,1839,1840,1841,1842,1843,1844,1845,1846,1847,1848,1849,1850,1851,1852,1853,1854,1855,1856,1857,1858,1859,1860,1861,1862,1863,1864,1865,1866,1867,1868,1869,1870,1871,1872,1873,1874,1875,1876,1877,1878,1879,1880,1881,1882,1883,1884,1885,1886,1887,1888,1889,1890,1891,1892,1893,1894,1895,1896,1897,1898,1899,1900,1901,1902,1903,1904,1905,1906,1907,1908,1909,1910,1911,1912,1913,1914,1915,1916,1917,1918,1919,1920,1921,1922,1923,1924,1925,1926,1927,1928,1929,1930,1931,1932,1933,1934,1935,1936,1937,1938,1939,1940,1941,1942,1943,1944,1945,1946,1947,1948,1949,1950,1951,1952,1953,1954,1955,1956,1957,1958,1959,1960,1961,1962,1963,1964,1965,1966,1967,1968,1969,1970,1971,1972,1973,1974,1975,1976,1977,1978,1979,1980,1981,1982,1983,1984,1985,1986,1987,1988,1989,1990,1991,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018,2019,2020,2021,2022,2023,2024,2025,2026,2027,2028,2029,2030,2031,2032,2033,2034,2035,2036,2037,2038,2039,2040,2041,2042,2043,2044,2045,2046,2047,2048,2049,2050,2051,2052,2053,2054,2055,2056,2057,2058,2059,2060,2061,2062,2063,2064,2065,2066,2067,2068,2069,2070,2071,2072,2073,2074,2075,2076,2077,2078,2079,2080,2081,2082,2083,2084,2085,2086,2087,2088,2089,2090,2091,2092,2093,2094,2095,2096,2097,2098,2099,2100,2101,2102,2103,2104,2105,2106,2107,2108,2109,2110,2111,2112,2113,2114,2115,2116,2117,2118,2119,2120,2121,2122,2123,2124,2125,2126,2127,2128,2129,2130,2131,2132,2133,2134,2135,2136,2137,2138,2139,2140,2141,2142,2143,2144,2145,2146,2147,2148,2149,2150,2151,2152,2153,2154,2155,2156,2157,2158,2159,2160,2161,2162,2163,2164,2165,2166,2167,2168,2169,2170,2171,2172,2173,2174,2175,2176,2177,2178,2179,2180,2181,2182,2183,2184,2185,2186,2187,2188,2189,2190,2191,2192,2193,2194,2195,2196,2197,2198,2199,2200,2201,2202,2203,2204,2205,2206,2207,2208,2209,2210,2211,2212,2213,2214,2215,2216,2217,2218,2219,2220,2221,2222,2223,2224,2225,2226,2227,2228,2229,2230,2231,2232,2233,2234,2235,2236,2237,2238,2239,2240,2241,2242,2243,2244,2245,2246,2247,2248,2249,2250,2251,2252,2253,2254,2255,2256,2257,2258,2259,2260,2261,2262,2263,2264,2265,2266,2267,2268,2269,2270,2271,2272,2273,2274,2275,2276,2277,2278,2279,2280,2281,2282,2283,2284,2285,2286,2287,2288,2289,2290,2291,2292,2293,2294,2295,2296,2297,2298,2299,2300,2301,2302,2303,2304,2305,2306,2307,2308,2309,2310,2311,2312,2313,2314,2315,2316,2317,2318,2319,2320,2321,2322,2323,2324,2325,2326,2327,2328,2329,2330,2331,2332,2333,2334,2335,2336,2337,2338,2339,2340,2341,2342,2343,2344,2345,2346,2347,2348,2349,2350,2351,2352,2353,2354,2355,2356,2357,2358,2359,2360,2361,2362,2363,2364,2365,2366,2367,2368,2369,2370,2371,2372,2373,2374,2375,2376,2377,2378,2379,2380,2381,2382,2383,2384,2385,2386,2387,2388,2389,2390,2391,2392,2393,2394,2395,2396,2397,2398,2399,2400,2401,2402,2403,2404,2405,2406,2407,2408,2409,2410,2411,2412,2413,2414,2415,2416,2417,2418,2419,2420,2421,2422,2423,2424,2425,2426,2427,2428,2429,2430,2431,2432,2433,2434,2435,2436,2437,2438,2439,2440,2441,2442,2443,2444,2445,2446,2447,2448,2449,2450,2451,2452,2453,2454,2455,2456,2457,2458,2459,2460,2461,2462,2463,2464,2465,2466,2467,2468,2469,2470,2471,2472,2473,2474,2475,2476,2477,2478,2479,2480,2481,2482,2483,2484,2485,2486,2487,2488,2489,2490,2491,2492,2493,2494,2495,2496,2497,2498,2499,2500,2501,2502,2503,2504,2505,2506,2507,2508,2509,2510,2511,2512,2513,2514,2515,2516,2517,2518,2519,2520,2521,2522,2523,2524,2525,2526,2527,2528,2529,2530,2531,2532,2533,2534,2535,2536,2537,2538,2539,2540,2541,2542,2543,2544,2545,2546,2547,2548,2549,2550,2551,2552,2553,2554,2555,2556,2557,2558,2559,2560,2561,2562,2563,2564,2565,2566,2567,2568,2569,2570,2571,2572,2573,2574,2575,2576,2577,2578,2579,2580,2581,2582,2583,2584,2585,2586,2587,2588,2589,2590,2591,2592,2593,2594,2595,2596,2597,2598,2599,2600,2601,2602,2603,2604,2605,2606,2607,2608,2609,2610,2611,2612,2613,2614,2615,2616,2617,2618,2619,2620,2621,2622,2623,2624,2625,2626,2627,2628,2629,2630,2631,2632,2633,2634,2635,2636,2637,2638,2639,2640,2641,2642,2643,2644,2645,2646,2647,2648,2649,2650,2651,2652,2653,2654,2655,2656,2657,2658,2659,2660,2661,2662,2663,2664,2665,2666,2667,2668,2669,2670,2671,2672,2673,2674,2675,2676,2677,2678,2679,2680,2681,2682,2683,2684,2685,2686,2687,2688,2689,2690,2691,2692,2693,2694,2695,2696,2697,2698,2699,2700,2701,2702,2703,2704,2705,2706,2707,2708,2709,2710,2711,2712,2713,2714,2715,2716,2717,2718,2719,2720,2721,2722,2723,2724,2725,2726,2727,2728,2729,2730,2731,2732,2733,2734,2735,2736,2737,2738,2739,2740,2741,2742,2743,2744,2745,2746,2747,2748,2749,2750,2751,2752,2753,2754,2755,2756,2757,2758,2759,2760,2761,2762,2763,2764,2765,2766,2767,2768,2769,2770,2771,2772,2773,2774,2775,2776,2777,2778,2779,2780,2781,2782,2783,2784,2785,2786,2787,2788,2789,2790,2791,2792,2793,2794,2795,2796,2797,2798,2799,2800,2801,2802,2803,2804,2805,2806,2807,2808,2809,2810,2811,2812,2813,2814,2815,2816,2817,2818,2819,2820,2821,2822,2823,2824,2825,2826,2827,2828,2829,2830,2831,2832,2833,2834,2835,2836,2837,2838,2839,2840,2841,2842,2843,2844,2845,2846,2847,2848,2849,2850,2851,2852,2853,2854,2855,2856,2857,2858,2859,2860,2861,2862,2863,2864,2865,2866,2867,2868,2869,2870,2871,2872,2873,2874,2875,2876,2877,2878,2879,2880,2881,2882,2883,2884,2885,2886,2887,2888,2889,2890,2891,2892,2893,2894,2895,2896,2897,2898,2899,2900,2901,2902,2903,2904,2905,2906,2907,2908,2909,2910,2911,2912,2913,2914,2915,2916,2917,2918,2919,2920,2921,2922,2923,2924,2925,2926,2927,2928,2929,2930,2931,2932,2933,2934,2935,2936,2937,2938,2939,2940,2941,2942,2943,2944,2945,2946,2947,2948,2949,2950,2951,2952,2953,2954,2955,2956,2957,2958,2959,2960,2961,2962,2963,2964,2965,2966,2967,2968,2969,2970,2971,2972,2973,2974,2975,2976,2977,2978,2979,2980,2981,2982,2983,2984,2985,2986,2987,2988,2989,2990,2991,2992,2993,2994,2995,2996,2997,2998,2999,3000,3001,3002,3003,3004,3005,3006,3007,3008,3009,3010,3011,3012,3013,3014,3015,3016,3017,3018,3019,3020,3021,3022,3023,3024,3025,3026,3027,3028,3029,3030,3031,3032,3033,3034,3035,3036,3037,3038,3039,3040,3041,3042,3043,3044,3045,3046,3047,3048,3049,3050,3051,3052,3053,3054,3055,3056,3057,3058,3059,3060,3061,3062,3063,3064,3065,3066,3067,3068,3069,3070,3071,3072,3073,3074,3075,3076,3077,3078,3079,3080,3081,3082,3083,3084,3085,3086,3087,3088,3089,3090,3091,3092,3093,3094,3095,3096,3097,3098,3099,3100,3101,3102,3103,3104,3105,3106,3107,3108,3109,3110,3111,3112,3113,3114,3115,3116,3117,3118,3119,3120,3121,3122,3123,3124,3125,3126,3127,3128,3129,3130,3131,3132,3133,3134,3135,3136,3137,3138,3139,3140,3141,3142,3143,3144,3145,3146,3147,3148,3149,3150,3151,3152,3153,3154,3155,3156,3157,3158,3159,3160,3161,3162,3163,3164,3165,3166,3167,3168,3169,3170,3171,3172,3173,3174,3175,3176,3177,3178,3179,3180,3181,3182,3183,3184,3185,3186,3187,3188,3189,3190,3191,3192,3193,3194,3195,3196,3197,3198,3199,3200,3201,3202,3203,3204,3205,3206,3207,3208,3209,3210,3211,3212,3213,3214,3215,3216,3217,3218,3219,3220,3221,3222,3223,3224,3225,3226,3227,3228,3229,3230,3231,3232,3233,3234,3235,3236,3237,3238,3239,3240,3241,3242,3243,3244,3245,3246,3247,3248,3249,3250,3251,3252,3253,3254,3255,3256,3257,3258,3259,3260,3261,3262,3263,3264,3265,3266,3267,3268,3269,3270,3271,3272,3273,3274,3275,3276,3277,3278,3279,3280,3281,3282,3283,3284,3285,3286,3287,3288,3289,3290,3291,3292,3293,3294,3295,3296,3297,3298,3299,3300,3301,3302,3303,3304,3305,3306,3307,3308,3309,3310,3311,3312,3313,3314,3315,3316,3317,3318,3319,3320,3321,3322,3323,3324,3325,3326,3327,3328,3329,3330,3331,3332,3333,3334,3335,3336,3337,3338,3339,3340,3341,3342,3343,3344,3345,3346,3347,3348,3349,3350,3351,3352,3353,3354,3355,3356,3357,3358,3359,3360,3361,3362,3363,3364,3365,3366,3367,3368,3369,3370,3371,3372,3373,3374,3375,3376,3377,3378,3379,3380,3381,3382,3383,3384,3385,3386,3387,3388,3389,3390,3391,3392,3393,3394,3395,3396,3397,3398,3399,3400,3401,3402,3403,3404,3405,3406,3407,3408,3409,3410,3411,3412,3413,3414,3415,3416,3417,3418,3419,3420,3421,3422,3423,3424,3425,3426,3427,3428,3429,3430,3431,3432,3433,3434,3435,3436,3437,3438,3439,3440,3441,3442,3443,3444,3445,3446,3447,3448,3449,3450,3451,3452,3453,3454,3455,3456,3457,3458,3459,3460,3461,3462,3463,3464,3465,3466,3467,3468,3469,3470,3471,3472,3473,3474,3475,3476,3477,3478,3479,3480,3481,3482,3483,3484,3485,3486,3487,3488,3489,3490,3491,3492,3493,3494,3495,3496,3497,3498,3499,3500,3501,3502,3503,3504,3505,3506,3507,3508,3509,3510,3511,3512,3513,3514,3515,3516,3517,3518,3519,3520,3521,3522,3523,3524,3525,3526,3527,3528,3529,3530,3531,3532,3533,3534,3535,3536,3537,3538,3539,3540,3541,3542,3543,3544,3545,3546,3547,3548,3549,3550,3551,3552,3553,3554,3555,3556,3557,3558,3559,3560,3561,3562,3563,3564,3565,3566,3567,3568,3569,3570,3571,3572,3573,3574,3575,3576,3577,3578,3579,3580,3581,3582,3583,3584,3585,3586,3587,3588,3589,3590,3591,3592,3593,3594,3595,3596,3597,3598,3599,3600,3601,3602,3603,3604,3605,3606,3607,3608,3609,3610,3611,3612,3613,3614,3615,3616,3617,3618,3619,3620,3621,3622,3623,3624,3625,3626,3627,3628,3629,3630,3631,3632,3633,3634,3635,3636,3637,3638,3639,3640,3641,3642,3643,3644,3645,3646,3647,3648,3649,3650,3651,3652,3653,3654,3655,3656,3657,3658,3659,3660,3661,3662,3663,3664,3665,3666,3667,3668,3669,3670,3671,3672,3673,3674,3675,3676,3677,3678,3679,3680,3681,3682,3683,3684,3685,3686,3687,3688,3689,3690,3691,3692,3693,3694,3695,3696,3697,3698,3699,3700,3701,3702,3703,3704,3705,3706,3707,3708,3709,3710,3711,3712,3713,3714,3715,3716,3717,3718,3719,3720,3721,3722,3723,3724,3725,3726,3727,3728,3729,3730,3731,3732,3733,3734,3735,3736,3737,3738,3739,3740,3741,3742,3743,3744,3745,3746,3747,3748,3749,3750,3751,3752,3753,3754,3755,3756,3757,3758,3759,3760,3761,3762,3763,3764,3765,3766,3767,3768,3769,3770,3771,3772,3773,3774,3775,3776,3777,3778,3779,3780,3781,3782,3783,3784,3785,3786,3787,3788,3789,3790,3791,3792,3793,3794,3795,3796,3797,3798,3799,3800,3801,3802,3803,3804,3805,3806,3807,3808,3809,3810,3811,3812,3813,3814,3815,3816,3817,3818,3819,3820,3821,3822,3823,3824,3825,3826,3827,3828,3829,3830,3831,3832,3833,3834,3835,3836,3837,3838,3839,3840,3841,3842,3843,3844,3845,3846,3847,3848,3849,3850,3851,3852,3853,3854,3855,3856,3857,3858,3859,3860,3861,3862,3863,3864,3865,3866,3867,3868,3869,3870,3871,3872,3873,3874,3875,3876,3877,3878,3879,3880,3881,3882,3883,3884,3885,3886,3887,3888,3889,3890,3891,3892,3893,3894,3895,3896,3897,3898,3899,3900,3901,3902,3903,3904,3905,3906,3907,3908,3909,3910,3911,3912,3913,3914,3915,3916,3917,3918,3919,3920,3921,3922,3923,3924,3925,3926,3927,3928,3929,3930,3931,3932,3933,3934,3935,3936,3937,3938,3939,3940,3941,3942,3943,3944,3945,3946,3947,3948,3949,3950,3951,3952,3953,3954,3955,3956,3957,3958,3959,3960,3961,3962,3963,3964,3965,3966,3967,3968,3969,3970,3971,3972,3973,3974,3975,3976,3977,3978,3979,3980,3981,3982,3983,3984,3985,3986,3987,3988,3989,3990,3991,3992,3993,3994,3995,3996,3997,3998,3999,4000,4001,4002,4003,4004,4005,4006,4007,4008,4009,4010,4011,4012,4013,4014,4015,4016,4017,4018,4019,4020,4021,4022,4023,4024,4025,4026,4027,4028,4029,4030,4031,4032,4033,4034,4035,4036,4037,4038,4039,4040,4041,4042,4043,4044,4045,4046,4047,4048,4049,4050,4051,4052,4053,4054,4055,4056,4057,4058,4059,4060,4061,4062,4063,4064,4065,4066,4067,4068,4069,4070,4071,4072,4073,4074,4075,4076,4077,4078,4079,4080,4081,4082,4083,4084,4085,4086,4087,4088,4089,4090,4091,4092,4093,4094,4095,4096,4097,4098,4099,4100,4101,4102,4103,4104,4105,4106,4107,4108,4109,4110,4111,4112,4113,4114,4115,4116,4117,4118,4119,4120,4121,4122,4123,4124,4125,4126,4127,4128,4129,4130,4131,4132,4133,4134,4135,4136,4137,4138,4139,4140,4141,4142,4143,4144,4145,4146,4147,4148,4149,4150,4151,4152,4153,4154,4155,4156,4157,4158,4159,4160,4161,4162,4163,4164,4165,4166,4167,4168,4169,4170,4171,4172,4173,4174,4175,4176,4177,4178,4179,4180,4181,4182,4183,4184,4185,4186,4187,4188,4189,4190,4191,4192,4193,4194,4195,4196,4197,4198,4199,4200,4201,4202,4203,4204,4205,4206,4207,4208,4209,4210,4211,4212,4213,4214,4215,4216,4217,4218,4219,4220,4221,4222,4223,4224,4225,4226,4227,4228,4229,4230,4231,4232,4233,4234,4235,4236,4237,4238,4239,4240,4241,4242,4243,4244,4245,4246,4247,4248,4249,4250,4251,4252,4253,4254,4255,4256,4257,4258,4259,4260,4261,4262,4263,4264,4265,4266,4267,4268,4269,4270,4271,4272,4273,4274,4275,4276,4277,4278,4279,4280,4281,4282,4283,4284,4285,4286,4287,4288,4289,4290,4291,4292,4293,4294,4295,4296,4297,4298,4299,4300,4301,4302,4303,4304,4305,4306,4307,4308,4309,4310,4311,4312,4313,4314,4315,4316,4317,4318,4319,4320,4321,4322,4323,4324,4325,4326,4327,4328,4329,4330,4331,4332,4333,4334,4335,4336,4337,4338,4339,4340,4341,4342,4343,4344,4345,4346,4347,4348,4349,4350,4351,4352,4353,4354,4355,4356,4357,4358,4359,4360,4361,4362,4363,4364,4365,4366,4367,4368,4369,4370,4371,4372,4373,4374,4375,4376,4377,4378,4379,4380,4381,4382,4383,4384,4385,4386,4387,4388,4389,4390,4391,4392,4393,4394,4395,4396,4397,4398,4399,4400,4401,4402,4403,4404,4405,4406,4407,4408,4409,4410,4411,4412,4413,4414,4415,4416,4417,4418,4419,4420,4421,4422,4423,4424,4425,4426,4427,4428,4429,4430,4431,4432,4433,4434,4435,4436,4437,4438,4439,4440,4441,4442,4443,4444,4445,4446,4447,4448,4449,4450,4451,4452,4453,4454,4455,4456,4457,4458,4459,4460,4461,4462,4463,4464,4465,4466,4467,4468,4469,4470,4471,4472,4473,4474,4475,4476,4477,4478,4479,4480,4481,4482,4483,4484,4485,4486,4487,4488,4489,4490,4491,4492,4493,4494,4495,4496,4497,4498,4499,4500,4501,4502,4503,4504,4505,4506,4507,4508,4509,4510,4511,4512,4513,4514,4515,4516,4517,4518,4519,4520,4521,4522,4523,4524,4525,4526,4527,4528,4529,4530,4531,4532,4533,4534,4535,4536,4537,4538,4539,4540,4541,4542,4543,4544,4545,4546,4547,4548,4549,4550,4551,4552,4553,4554,4555,4556,4557,4558,4559,4560,4561,4562,4563,4564,4565,4566,4567,4568,4569,4570,4571,4572,4573,4574,4575,4576,4577,4578,4579,4580,4581,4582,4583,4584,4585,4586,4587,4588,4589,4590,4591,4592,4593,4594,4595,4596,4597,4598,4599,4600,4601,4602,4603,4604,4605,4606,4607,4608,4609,4610,4611,4612,4613,4614,4615,4616,4617,4618,4619,4620,4621,4622,4623,4624,4625,4626,4627,4628,4629,4630,4631,4632,4633,4634,4635,4636,4637,4638,4639,4640,4641,4642,4643,4644,4645,4646,4647,4648,4649,4650,4651,4652,4653,4654,4655,4656,4657,4658,4659,4660,4661,4662,4663,4664,4665,4666,4667,4668,4669,4670,4671,4672,4673,4674,4675,4676,4677,4678,4679,4680,4681,4682,4683,4684,4685,4686,4687,4688,4689,4690,4691,4692,4693,4694,4695,4696,4697,4698,4699,4700,4701,4702,4703,4704,4705,4706,4707,4708,4709,4710,4711,4712,4713,4714,4715,4716,4717,4718,4719,4720,4721,4722,4723,4724,4725,4726,4727,4728,4729,4730,4731,4732,4733,4734,4735,4736,4737,4738,4739,4740,4741,4742,4743,4744,4745,4746,4747,4748,4749,4750,4751,4752,4753,4754,4755,4756,4757,4758,4759,4760,4761,4762,4763,4764,4765,4766,4767,4768,4769,4770,4771,4772,4773,4774,4775,4776,4777,4778,4779,4780,4781,4782,4783,4784,4785,4786,4787,4788,4789,4790,4791,4792,4793,4794,4795,4796,4797,4798,4799,4800,4801,4802,4803,4804,4805,4806,4807,4808,4809,4810,4811,4812,4813,4814,4815,4816,4817,4818,4819,4820,4821,4822,4823,4824,4825,4826,4827,4828,4829,4830,4831,4832,4833,4834,4835,4836,4837,4838,4839,4840,4841,4842,4843,4844,4845,4846,4847,4848,4849,4850,4851,4852,4853,4854,4855,4856,4857,4858,4859,4860,4861,4862,4863,4864,4865,4866,4867,4868,4869,4870,4871,4872,4873,4874,4875,4876,4877,4878,4879,4880,4881,4882,4883,4884,4885,4886,4887,4888,4889,4890,4891,4892,4893,4894,4895,4896,4897,4898,4899,4900,4901,4902,4903,4904,4905,4906,4907,4908,4909,4910,4911,4912,4913,4914,4915,4916,4917,4918,4919,4920,4921,4922,4923,4924,4925,4926,4927,4928,4929,4930,4931,4932,4933,4934,4935,4936,4937,4938,4939,4940,4941,4942,4943,4944,4945,4946,4947,4948,4949,4950,4951,4952,4953,4954,4955,4956,4957,4958,4959,4960,4961,4962,4963,4964,4965,4966,4967,4968,4969,4970,4971,4972,4973,4974,4975,4976,4977,4978,4979,4980,4981,4982,4983,4984,4985,4986,4987,4988,4989,4990,4991,4992,4993,4994,4995,4996,4997,4998,4999,5000,5001,5002,5003,5004,5005,5006,5007,5008,5009,5010,5011,5012,5013,5014,5015,5016,5017,5018,5019,5020,5021,5022,5023,5024,5025,5026,5027,5028,5029,5030,5031,5032,5033,5034,5035,5036,5037,5038,5039,5040,5041,5042,5043,5044,5045,5046,5047,5048,5049,5050,5051,5052,5053,5054,5055,5056,5057,5058,5059,5060,5061,5062,5063,5064,5065,5066,5067,5068,5069,5070,5071,5072,5073,5074,5075,5076,5077,5078,5079,5080,5081,5082,5083,5084,5085,5086,5087,5088,5089,5090,5091,5092,5093,5094,5095,5096,5097,5098,5099,5100,5101,5102,5103,5104,5105,5106,5107,5108,5109,5110,5111,5112,5113,5114,5115,5116,5117,5118,5119,5120,5121,5122,5123,5124,5125,5126,5127,5128,5129,5130,5131,5132,5133,5134,5135,5136,5137,5138,5139,5140,5141,5142,5143,5144,5145,5146,5147,5148,5149,5150,5151,5152,5153,5154,5155,5156,5157,5158,5159,5160,5161,5162,5163,5164,5165,5166,5167,5168,5169,5170,5171,5172,5173,5174,5175,5176,5177,5178,5179,5180,5181,5182,5183,5184,5185,5186,5187,5188,5189,5190,5191,5192,5193,5194,5195,5196,5197,5198,5199,5200,5201,5202,5203,5204,5205,5206,5207,5208,5209,5210,5211,5212,5213,5214,5215,5216,5217,5218,5219,5220,5221,5222,5223,5224,5225,5226,5227,5228,5229,5230,5231,5232,5233,5234,5235,5236,5237,5238,5239,5240,5241,5242,5243,5244,5245,5246,5247,5248,5249,5250,5251,5252,5253,5254,5255,5256,5257,5258,5259,5260,5261,5262,5263,5264,5265,5266,5267,5268,5269,5270,5271,5272,5273,5274,5275,5276,5277,5278,5279,5280,5281,5282,5283,5284,5285,5286,5287,5288,5289,5290,5291,5292,5293,5294,5295,5296,5297,5298,5299,5300,5301,5302,5303,5304,5305,5306,5307,5308,5309,5310,5311,5312,5313,5314,5315,5316,5317,5318,5319,5320,5321,5322,5323,5324,5325,5326,5327,5328,5329,5330,5331,5332,5333,5334,5335,5336,5337,5338,5339,5340,5341,5342,5343,5344,5345,5346,5347,5348,5349,5350,5351,5352,5353,5354,5355,5356,5357,5358,5359,5360,5361,5362,5363,5364,5365,5366,5367,5368,5369,5370,5371,5372,5373,5374,5375,5376,5377,5378,5379,5380,5381,5382,5383,5384,5385,5386,5387,5388,5389,5390,5391,5392,5393,5394,5395,5396,5397,5398,5399,5400,5401,5402,5403,5404,5405,5406,5407,5408,5409,5410,5411,5412,5413,5414,5415,5416,5417,5418,5419,5420,5421,5422,5423,5424,5425,5426,5427,5428,5429,5430,5431,5432,5433,5434,5435,5436,5437,5438,5439,5440,5441,5442,5443,5444,5445,5446,5447,5448,5449,5450,5451,5452,5453,5454,5455,5456,5457,5458,5459,5460,5461,5462,5463,5464,5465,5466,5467,5468,5469,5470,5471,5472,5473,5474,5475,5476,5477,5478,5479,5480,5481,5482,5483,5484,5485,5486,5487,5488,5489,5490,5491,5492,5493,5494,5495,5496,5497,5498,5499,5500,5501,5502,5503,5504,5505,5506,5507,5508,5509,5510,5511,5512,5513,5514,5515,5516,5517,5518,5519,5520,5521,5522,5523,5524,5525,5526,5527,5528,5529,5530,5531,5532,5533,5534,5535,5536,5537,5538,5539,5540,5541,5542,5543,5544,5545,5546,5547,5548,5549,5550,5551,5552,5553,5554,5555,5556,5557,5558,5559,5560,5561,5562,5563,5564,5565,5566,5567,5568,5569,5570,5571,5572,5573,5574,5575,5576,5577,5578,5579,5580,5581,5582,5583,5584,5585,5586,5587,5588,5589,5590,5591,5592,5593,5594,5595,5596,5597,5598,5599,5600,5601,5602,5603,5604,5605,5606,5607,5608,5609,5610,5611,5612,5613,5614,5615,5616,5617,5618,5619,5620,5621,5622,5623,5624,5625,5626,5627,5628,5629,5630,5631,5632,5633,5634,5635,5636,5637,5638,5639,5640,5641,5642,5643,5644,5645,5646,5647,5648,5649,5650,5651,5652,5653,5654,5655,5656,5657,5658,5659,5660,5661,5662,5663,5664,5665,5666,5667,5668,5669,5670,5671,5672,5673,5674,5675,5676,5677,5678,5679,5680,5681,5682,5683,5684,5685,5686,5687,5688,5689,5690,5691,5692,5693,5694,5695,5696,5697,5698,5699,5700,5701,5702,5703,5704,5705,5706,5707,5708,5709,5710,5711,5712,5713,5714,5715,5716,5717,5718,5719,5720,5721,5722,5723,5724,5725,5726,5727,5728,5729,5730,5731,5732,5733,5734,5735,5736,5737,5738,5739,5740,5741,5742,5743,5744,5745,5746,5747,5748,5749,5750,5751,5752,5753,5754,5755,5756,5757,5758,5759,5760,5761,5762,5763,5764,5765,5766,5767,5768,5769,5770,5771,5772,5773,5774,5775,5776,5777,5778,5779,5780,5781,5782,5783,5784,5785,5786,5787,5788,5789,5790,5791,5792,5793,5794,5795,5796,5797,5798,5799,5800,5801,5802,5803,5804,5805,5806,5807,5808,5809,5810,5811,5812,5813,5814,5815,5816,5817,5818,5819,5820,5821,5822,5823,5824,5825,5826,5827,5828,5829,5830,5831,5832,5833,5834,5835,5836,5837,5838,5839,5840,5841,5842,5843,5844,5845,5846,5847,5848,5849,5850,5851,5852,5853,5854,5855,5856,5857,5858,5859,5860,5861,5862,5863,5864,5865,5866,5867,5868,5869,5870,5871,5872,5873,5874,5875,5876,5877,5878,5879,5880,5881,5882,5883,5884,5885,5886,5887,5888,5889,5890,5891,5892,5893,5894,5895,5896,5897,5898,5899,5900,5901,5902,5903,5904,5905,5906,5907,5908,5909,5910,5911,5912,5913,5914,5915,5916,5917,5918,5919,5920,5921,5922,5923,5924,5925,5926,5927,5928,5929,5930,5931,5932,5933,5934,5935,5936,5937,5938,5939,5940,5941,5942,5943,5944,5945,5946,5947,5948,5949,5950,5951,5952,5953,5954,5955,5956,5957,5958,5959,5960,5961,5962,5963,5964,5965,5966,5967,5968,5969,5970,5971,5972,5973,5974,5975,5976,5977,5978,5979,5980,5981,5982,5983,5984,5985,5986,5987,5988,5989,5990,5991,5992,5993,5994,5995,5996,5997,5998,5999,6000,6001,6002,6003,6004,6005,6006,6007,6008,6009,6010,6011,6012,6013,6014,6015,6016,6017,6018,6019,6020,6021,6022,6023,6024,6025,6026,6027,6028,6029,6030,6031,6032,6033,6034,6035,6036,6037,6038,6039,6040,6041,6042,6043,6044,6045,6046,6047,6048,6049,6050,6051,6052,6053,6054,6055,6056,6057,6058,6059,6060,6061,6062,6063,6064,6065,6066,6067,6068,6069,6070,6071,6072,6073,6074,6075,6076,6077,6078,6079,6080,6081,6082,6083,6084,6085,6086,6087,6088,6089,6090,6091,6092,6093,6094,6095,6096,6097,6098,6099,6100,6101,6102,6103,6104,6105,6106,6107,6108,6109,6110,6111,6112,6113,6114,6115,6116,6117,6118,6119,6120,6121,6122,6123,6124,6125,6126,6127,6128,6129,6130,6131,6132,6133,6134,6135,6136,6137,6138,6139,6140,6141,6142,6143,6144,6145,6146,6147,6148,6149,6150,6151,6152,6153,6154,6155,6156,6157,6158,6159,6160,6161,6162,6163,6164,6165,6166,6167,6168,6169,6170,6171,6172,6173,6174,6175,6176,6177,6178,6179,6180,6181,6182,6183,6184,6185,6186,6187,6188,6189,6190,6191,6192,6193,6194,6195,6196,6197,6198,6199,6200,6201,6202,6203,6204,6205,6206,6207,6208,6209,6210,6211,6212,6213,6214,6215,6216,6217,6218,6219,6220,6221,6222,6223,6224,6225,6226,6227,6228,6229,6230,6231,6232,6233,6234,6235,6236,6237,6238,6239,6240,6241,6242,6243,6244,6245,6246,6247,6248,6249,6250,6251,6252,6253,6254,6255,6256,6257,6258,6259,6260,6261,6262,6263,6264,6265,6266,6267,6268,6269,6270,6271,6272,6273,6274,6275,6276,6277,6278,6279,6280,6281,6282,6283,6284,6285,6286,6287,6288,6289,6290,6291,6292,6293,6294,6295,6296,6297,6298,6299,6300,6301,6302,6303,6304,6305,6306,6307,6308,6309,6310,6311,6312,6313,6314,6315,6316,6317,6318,6319,6320,6321,6322,6323,6324,6325,6326,6327,6328,6329,6330,6331,6332,6333,6334,6335,6336,6337,6338,6339,6340,6341,6342,6343,6344,6345,6346,6347,6348,6349,6350,6351,6352,6353,6354,6355,6356,6357,6358,6359,6360,6361,6362,6363,6364,6365,6366,6367,6368,6369,6370,6371,6372,6373,6374,6375,6376,6377,6378,6379,6380,6381,6382,6383,6384,6385,6386,6387,6388,6389,6390,6391,6392,6393,6394,6395,6396,6397,6398,6399,6400,6401,6402,6403,6404,6405,6406,6407,6408,6409,6410,6411,6412,6413,6414,6415,6416,6417,6418,6419,6420,6421,6422,6423,6424,6425,6426,6427,6428,6429,6430,6431,6432,6433,6434,6435,6436,6437,6438,6439,6440,6441,6442,6443,6444,6445,6446,6447,6448,6449,6450,6451,6452,6453,6454,6455,6456,6457,6458,6459,6460,6461,6462,6463,6464,6465,6466,6467,6468,6469,6470,6471,6472,6473,6474,6475,6476,6477,6478,6479,6480,6481,6482,6483,6484,6485,6486,6487,6488,6489,6490,6491,6492,6493,6494,6495,6496,6497,6498,6499,6500,6501,6502,6503,6504,6505,6506,6507,6508,6509,6510,6511,6512,6513,6514,6515,6516,6517,6518,6519,6520,6521,6522,6523,6524,6525,6526,6527,6528,6529,6530,6531,6532,6533,6534,6535,6536,6537,6538,6539,6540,6541,6542,6543,6544,6545,6546,6547,6548,6549,6550,6551,6552,6553,6554,6555,6556,6557,6558,6559,6560,6561,6562,6563,6564,6565,6566,6567,6568,6569,6570,6571,6572,6573,6574,6575,6576,6577,6578,6579,6580,6581,6582,6583,6584,6585,6586,6587,6588,6589,6590,6591,6592,6593,6594,6595,6596,6597,6598,6599,6600,6601,6602,6603,6604,6605,6606,6607,6608,6609,6610,6611,6612,6613,6614,6615,6616,6617,6618,6619,6620,6621,6622,6623,6624,6625,6626,6627,6628,6629,6630,6631,6632,6633,6634,6635,6636,6637,6638,6639,6640,6641,6642,6643,6644,6645,6646,6647,6648,6649,6650,6651,6652,6653,6654,6655,6656,6657,6658,6659,6660,6661,6662,6663,6664,6665,6666,6667,6668,6669,6670,6671,6672,6673,6674,6675,6676,6677,6678,6679,6680,6681,6682,6683,6684,6685,6686,6687,6688,6689,6690,6691,6692,6693,6694,6695,6696,6697,6698,6699,6700,6701,6702,6703,6704,6705,6706,6707,6708,6709,6710,6711,6712,6713,6714,6715,6716,6717,6718,6719,6720,6721,6722,6723,6724,6725,6726,6727,6728,6729,6730,6731,6732,6733,6734,6735,6736,6737,6738,6739,6740,6741,6742,6743,6744,6745,6746,6747,6748,6749,6750,6751,6752,6753,6754,6755,6756,6757,6758,6759,6760,6761,6762,6763,6764,6765,6766,6767,6768,6769,6770,6771,6772,6773,6774,6775,6776,6777,6778,6779,6780,6781,6782,6783,6784,6785,6786,6787,6788,6789,6790,6791,6792,6793,6794,6795,6796,6797,6798,6799,6800,6801,6802,6803,6804,6805,6806,6807,6808,6809,6810,6811,6812,6813,6814,6815,6816,6817,6818,6819,6820,6821,6822,6823,6824,6825,6826,6827,6828,6829,6830,6831,6832,6833,6834,6835,6836,6837,6838,6839,6840,6841,6842,6843,6844,6845,6846,6847,6848,6849,6850,6851,6852,6853,6854,6855,6856,6857,6858,6859,6860,6861,6862,6863,6864,6865,6866,6867,6868,6869,6870,6871,6872,6873,6874,6875,6876,6877,6878,6879,6880,6881,6882,6883,6884,6885,6886,6887,6888,6889,6890,6891,6892,6893,6894,6895,6896,6897,6898,6899,6900,6901,6902,6903,6904,6905,6906,6907,6908,6909,6910,6911,6912,6913,6914,6915,6916,6917,6918,6919,6920,6921,6922,6923,6924,6925,6926,6927,6928,6929,6930,6931,6932,6933,6934,6935,6936,6937,6938,6939,6940,6941,6942,6943,6944,6945,6946,6947,6948,6949,6950,6951,6952,6953,6954,6955,6956,6957,6958,6959,6960,6961,6962,6963,6964,6965,6966,6967,6968,6969,6970,6971,6972,6973,6974,6975,6976,6977,6978,6979,6980,6981,6982,6983,6984,6985,6986,6987,6988,6989,6990,6991,6992,6993,6994,6995,6996,6997,6998,6999,7000,7001,7002,7003,7004,7005,7006,7007,7008,7009,7010,7011,7012,7013,7014,7015,7016,7017,7018,7019,7020,7021,7022,7023,7024,7025,7026,7027,7028,7029,7030,7031,7032,7033,7034,7035,7036,7037,7038,7039,7040,7041,7042,7043,7044,7045,7046,7047,7048,7049,7050,7051,7052,7053,7054,7055,7056,7057,7058,7059,7060,7061,7062,7063,7064,7065,7066,7067,7068,7069,7070,7071,7072,7073,7074,7075,7076,7077,7078,7079,7080,7081,7082,7083,7084,7085,7086,7087,7088,7089,7090,7091,7092,7Interrupted.

```
```Prelude> [2,4,6,8,10]
[2,4,6,8,10]
Prelude> [2,4,6,8,10] !! 4
10
Prelude> [42..] !! 100
142
Prelude> tail([42..]) !! 100
143
```
The Sieve of Eratosthenes is a technique for computing prime numbers that starts with a list of sorted numbers and moves across the list eliminating multiples of each prime as it is discovered. This is illustrated by the following video:

The following is a Haskell function that uses infinite lists and lazy evaluation to computes prime numbers with the Sieve of Eratosthenes (Source: Literate Programs*).

```
Prelude> let sieve (p:xs) = p : sieve [x|x <- xs, x `mod` p > 0]
Prelude> let primes = sieve [2..]
Prelude> primes !! 0
2
Prelude> primes !! 5
13
Prelude> primes
[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,1163,1171,1181,1187,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1277,1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,1381,1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,1669,1693,1697,1699,1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,1823,1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,1951,1973,1979,1987,1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,2063,2069,2081,2083,2087,2089,2099,2111,2113,2129,2131,2137,2141,2143,2153,2161,2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,2293,2297,2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,2399,2411,Interrupted.
```

Some languages, including Scheme (a dialect of Lisp distinct from Common Lisp) include constructs that allow programmers to explicitly delay evaluation of individual expressions, essentially allowing lazy evaluation on an expression-by-expression basis.

Assignment Statements
Conditional Targets

C++ and Perl are a couple of languages which allow conditional targets. While Java supports the ternary conditional, it does not support conditional targets. Consider this C++ program:

```#include <iostream>

int main(){
int flag = 0;
int x = 100;
int y = 100;
(flag ? x : y) = 0;
printf("X: %d, Y: %d\n", x, y);
}

--------------------------------------------
timberlake {~/cse305-ta-sp10/assign} > g++ CondTar.cpp
timberlake {~/cse305-ta-sp10/assign} > ./a.out
X: 100, Y: 0
```
Here `(flag ? x : y) = 0;` is equivalent to saying:
```if(flag) x = 0;
else y = 0;
```

Compound Assignment Operators
In the C-based languages and Python `x •= y;` means the same as `x = x • y;` for most operators, `•`.

Assignment as Expression
In Common Lisp and the C-based languages the assignment statement is also an expression that evaluates to the r-value that is stored in the l-value, and the assignment operator is right associative. For example, `i = j = k` assigns the value of `k` to `j` and then to `i`.

In Perl the value of the assignment operation is the l-value of the left-hand side, even though assignment is still right-associative. The l-value is dereferenced to its r-value if the assignment expression is on a right-hand side, but if it's on a left-hand side, the l-value may be stored into. Here's an example, based on L. Wall, T. Christiansen & J. Orwant, Programming Perl, (Sebastopol, CA: O'Reilly) p. 25.

```
#! /util/bin/perl

\$x = \$y = 3;

\$temp = 100;

(\$temp *= 9/5) += 32;

print "x = \$x, y = \$y, temp = \$temp\n";

-----------------------------------------
<timberlake:Test:1:42> perl assignment.perl
x = 3, y = 3, temp = 212
```

In Python, assignment statements like `i = j = k,` are allowed, even though a Python assignment statement is not an expression at all:

```
<wasat:~:1:108> python
Python 2.2.1 (#2, Jul 19 2002, 09:50:59) [C] on sunos5
>>> x = y = 3
>>> x
3
>>> y
3
>>> print(None)
None
>>> print(z=7)
File "", line 1
print(z=7)
^
SyntaxError: invalid syntax
```
Allowing an assignment statement to be an expression can lead to programmer error and difficult to read expressions, as in this C++ program:
```#include <iostream>

int main(){
int x = 5;

if(x = 2) printf("here\n"); // "==" mistakenly typed as "="
printf("x = %d\n", x);

x = 5;
int y = 2;
int z = 4;
int a = 0;

printf("x = %d, y = %d, z = %d, a = %d\n", x, y, z ,a);

int q = x - (a = y * z) / 3; // difficult to read

printf("x = %d, y = %d, z = %d, a = %d, q = %d\n", x, y, z ,a, q);

}
------------------------------------------------------------------
timberlake {~/cse305-ta-sp10/assign} > g++ CAssign.cpp
timberlake {~/cse305-ta-sp10/assign} > ./a.out
here
x = 2
x = 5, y = 2, z = 4, a = 0
x = 5, y = 2, z = 4, a = 8, q = 3
```

Unary Assignment Operators
These are our friends, the prefix and postfix `++` and `--`. The tricky issue is the postfix versions. In Java, it is clear that the semantics of `x++` in any context is `x fetch x x fetch 1 + store pop`. Here's an example:
```
public class UnaryAsngmnt {

public static void main (String[] args) {
int x=3, y = 0;

System.out.println("x = " + x);
System.out.println("y = " + y);

y = x + x++;
System.out.println();
System.out.println("y = x + x++;");
System.out.println("x = " + x);
System.out.println("y = " + y);

x = x++;
System.out.println();
System.out.println("x = x++;");
System.out.println("x = " + x);

} // end of main ()

}// UnaryAsngmnt

--------------------------------------------------
<cirrus:Programs:1:124> javac UnaryAsngmnt.java

<cirrus:Programs:1:125> java UnaryAsngmnt
x = 3
y = 0

y = x + x++;
x = 4
y = 6

x = x++;
x = 4
```

In C the tricky uses of these operators are officially undefined since the order of evaluation of operands is unspecified. Let's see this in two C compilers. In cc:

```
#include <stdio.h>

int main() {
int x=3, y=0;

printf("x = %d, y = %d\n", x, y);

y = x + x++;
printf("\ny = x + x++;\n");
printf("x = %d, y = %d\n", x, y);

x = x++;
printf("\nx = x++;\n");
printf("x = %d, y = %d\n", x, y);

x = x++ + x;
printf("\nx = x++ + x;\n");
printf("x = %d, y = %d\n", x, y);

x = x++ + x++;
printf("\nx = x++ + x++;\n");
printf("x = %d, y = %d\n", x, y);

return 0;
}
---------------------------------------------
<wasat:Programs:2:183> cc unaryAsngmnt.c -o unaryAsngmnt.out

<wasat:Programs:2:184> unaryAsngmnt.out
x = 3, y = 0

y = x + x++;
x = 4, y = 6

x = x++;
x = 5, y = 6

x = x++ + x;
x = 11, y = 6

x = x++ + x++;
x = 24, y = 6
```
and the same program, compiled by gcc:
```
<wasat:Programs:2:185> gcc -Wall unaryAsngmnt.c -o unaryAsngmnt.out
unaryAsngmnt.c: In function `main':
unaryAsngmnt.c:8: warning: operation on `x' may be undefined
unaryAsngmnt.c:12: warning: operation on `x' may be undefined
unaryAsngmnt.c:16: warning: operation on `x' may be undefined
unaryAsngmnt.c:20: warning: operation on `x' may be undefined
unaryAsngmnt.c:20: warning: operation on `x' may be undefined

<wasat:Programs:2:186> unaryAsngmnt.out
x = 3, y = 0

y = x + x++;
x = 4, y = 6

x = x++;
x = 5, y = 6

x = x++ + x;
x = 6, y = 6

x = x++ + x++;
x = 7, y = 6
```

Assignment Operand Order
The issue of operand order also applies to the operands of the assignment operator: which is evaluated first, the left-hand side or the right-hand side? To tell, we need to consider side-effects. In Java the left-to-right operand evaluation order still applies:
```
public class AsngmntOrder {

public static void main (String[] args) {
int i=0, a[] = {5, 5, 5};

System.out.println("i = " + i);
System.out.println("a = [" + a[0]
+ ", " + a[1]
+ ", " + a[2] + "]");

a[i] = i++;
System.out.println();
System.out.println("a[i] = i++;");
System.out.println("i = " + i);
System.out.println("a = [" + a[0]
+ ", " + a[1]
+ ", " + a[2] + "]");

a[i++] = i;
System.out.println();
System.out.println("a[i++] = i;");
System.out.println("i = " + i);
System.out.println("a = [" + a[0]
+ ", " + a[1]
+ ", " + a[2] + "]");
} // end of main ()

}// AsngmntOrder
------------------------------------------------
<cirrus:Programs:1:129> javac AsngmntOrder.java

<cirrus:Programs:1:130> java AsngmntOrder
i = 0
a = [5, 5, 5]

a[i] = i++;
i = 1
a = [0, 5, 5]

a[i++] = i;
i = 2
a = [0, 2, 5]
```

C leaves this case officially undefined,

```
This paragraph renders  undefined  statement  expressions
such as
i = ++i + 1;
a[i++] = i;                                       |
while allowing
i = i + 1;
a[i] = i;    [ISO CStandard, Sect. 6.5(#58)]

```

Parallel and Pattern Matching Assignment
A statement like `x = y = ... = <exp>` lets you assign the same value to multiple variables, but usually the assignment of multiple values to multiple variables requires multiple assignment statements in sequential order.

Common Lisp's assignment "statement" allows multiple values to be stored in multiple variables in sequential order:

```
cl-user(17): (setf x 1 y 2 z 3 x z)
3

cl-user(18): x
3

cl-user(19): y
2

cl-user(20): z
3
```
There is also a parallel version that allows multiple values to be stored in multiple variables in parallel order. This allows for the swapping of two variables without using an explicit temporary:
```
cl-user(21): x
3

cl-user(22): y
2

cl-user(23): (psetf x y y x)
nil

cl-user(24): x
2

cl-user(25): y
3
```
There's also a "respectively" version, that is useful, as we'll see later, when a function returns multiple values:
```cl-user(1): (setf x 2 y 3)
3
cl-user(2): x
2
cl-user(3): y
3
cl-user(4): (multiple-value-setq (x y) (values y x))
3
cl-user(5): x
3
cl-user(6): y
2
cl-user(7):
```

Several other languages, including Perl, Python, and Ruby, allow assignment statements with several variables in the LHS and several expressions in the RHS. Assignment of experssions to respective variables is done in parallel. For example, in Python:

```
<timberlake:Test:1:31> python
Python 2.6.4 (r264:75706, Dec 21 2009, 12:37:31)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-46)] on linux2
>>> x,y = 3,5
>>> x
3
>>> y
5
>>> x,y = y,x
>>> x
5
>>> y
3
```
Such an assignment statement is treated as having a tuple of variables on the LHS and a tuple of expressions on the RHS:
```>>> (x,y,z) = (3,3+3,3*3)
>>> x
3
>>> y
6
>>> z
9
```
This can be done with lists as well as tuples:
```>>> [(let1,name1), (let2,name2), (let3,name3)] = [("a","alfa"), ("b","brave"), ("c","charlie")]
>>> print let1, let2, let3
a b c
>>> print name1, name2, name3
alfa brave charlie
```
However, only variables may appear on the LHS, and no unbound variables may appear on the RHS:
```>>> (x,3,y) = (2,3,5)
File "", line 1
SyntaxError: can't assign to literal

>>> (x,y,z) = (2,u,5)
Traceback (most recent call last):
File "", line 1, in
NameError: name 'u' is not defined
```
In Python, the number of variables on the LHS must be the same as the number of expressions on the RHS:
```>>> x,y,z = 2,3
Traceback (most recent call last):
File "", line 1, in
ValueError: need more than 2 values to unpack

>>> x,y = 2,3,4
Traceback (most recent call last):
File "", line 1, in
ValueError: too many values to unpack
```
Ruby, however, allows this, It ignores the extra RHS values, and assigns the extra LHS variables the value `nil`:
```<timberlake:Test:1:37> irb
irb(main):001:0> x,y = 1,2,3
=> [1, 2, 3]
irb(main):002:0> x
=> 1
irb(main):003:0> y
=> 2
irb(main):004:0> x,y,z = 1,2
=> [1, 2]
irb(main):005:0> x
=> 1
irb(main):006:0> y
=> 2
irb(main):007:0> z
=> nil
```
Ruby's splat operator packs or unpacks RHS values:
```irb(main):018:0> x, *y, z = 1,2,3,4,5
=> [1, 2, 3, 4, 5]
irb(main):019:0> x
=> 1
irb(main):020:0> y
=> [2, 3, 4]
irb(main):021:0> z
=> 5

irb(main):022:0> w,x,y,z = [1], *[2,3], *[4,5]
=> [[1], 2, 3, 4, 5]
irb(main):023:0> w
=> [1]
irb(main):024:0> x
=> 2
irb(main):025:0> y
=> 3
irb(main):026:0> z
=> 4
```
Still, only variables may appear on the LHS, and no unbound variables may appear on the RHS:

In Haskell and Erlang, the parallel assignment is actually done by pattern matching, so values, as well as variables, may appear on the LHS, but will fail if they do not match. In Haskell,

```<timberlake:~:1:26> ghci
GHCi, version 6.12.1: http://www.haskell.org/ghc/  :? for help

Prelude> let [x,3,y] = [2+1, 6/2, 3*3]
Prelude> x
3.0
Prelude> y
9.0

Prelude> let [u,6,v] = [2,3,5]
Prelude> u
*** Exception: :1:4-20: Irrefutable pattern failed for pattern [u, 6, v]

Prelude> v
*** Exception: :1:4-20: Irrefutable pattern failed for pattern [u, 6, v]
```
Using the list construction operator ("`:`") in Haskell, we can use pattern matching to deconstruct a list:
```Prelude> let x:xs = [2,4..10]
Prelude> x
2
Prelude> xs
[4,6,8,10]
```
We can also do this in Erlang, where "`|`" is the list construction operator:
```<timberlake:~:1:28> erl
Erlang R13B03 (erts-5.7.4) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.7.4  (abort with ^G)
1> [X|Xs] = [2,4,6.8,10].
[2,4,6.8,10]

2> X.
2

3> Xs.
[4,6.8,10]
```
However, unbound variables still aren't allowed on the RHS of Haskell or Erlang assignment statements:
```<timberlake:~:1:29> erl
Erlang R13B03 (erts-5.7.4) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.7.4  (abort with ^G)

1> [X,3,Y] = [1,Z,4].
* 1: variable 'Z' is unbound
```

Prolog has the most sophisticated pattern matching, allowing variables on both sides of the operator:

```<timberlake:~:1:30> prolog
SICStus 4.0.5 (x86_64-linux-glibc2.3): Thu Feb 12 09:48:30 CET 2009
| ?- [X,3,Y] = [1,Z,4].
X = 1,
Y = 4,
Z = 3 ?
yes

| ?- [X,3,Y] = [1,Z,4], format("X=~d, Y=~d, Z=~d~n", [X,Y,Z]).
X=1, Y=4, Z=3
X = 1,
Y = 4,
Z = 3 ?
yes
```
Prolog's two-way pattern matching, called "unification", lets a variable on one side get bound to a value on that same side via a repeated variable on the other side:
```| ?- [U,V,9] = [X,6,X].
U = 9,
V = 6,
X = 9 ?
yes
```
Variable binding by pattern matching will be even more useful when we use it between formal parameters and actual arguments of functions.