Create an interpreter using JAVA

• ::=REM|REM
• ::= =
• ::=PRINT|PRINT |PRINT |PRINT
• ::=READ
• ::=IFTHEN
• ::=END.

Where:

::= |

::=a-z|A-Z

::= |

::= |

::= |

::= |

::=

::=.

::=

::=e|E

::=0|1|2|3|4|5|6|7|8|9

::=+|-

::=\"\"|\"\"

::=

::=.gt.|.lt.|.eq.|.ge.|.le.|.ne.

::=.or.|.and.|.not.

::= | |

A conditional expression must include logical or relational operators. Examples:

• 3.gt.5
• .not.3.gt.5
• 3.gt.5.and.3.eq.var
• .not.3.gt.5.and.3.eq.var

Thekeywordsare reserved words. They are:IF,THEN,READ,PRINT, andEND. In addition, the language is not case sensitive. An instruction with only thekeywordPRINTis equivalent to a new line when the instruction is executed by the interpreter. Moreover, the interpreter will ignore the comments statements.

The alphabet of the language is the characters in theASCII table. Additionally, the type of a variable is determined by the first letter of the variable name. The following table shows the previous:

First letter of the variable name	Variable type
A-F	integer
G-N	real
O-Z	string

The following table shows the results of the arithmetic operators according to the different types (integer, real, and string):

Arithmetic Operator	Operands	Result	Example
.add.	integer vs. integer	integer	2.add.2 => 4
real vs. real	real	2.0.add.2.0 => 4.0
real vs. integer	real	2.0.add.2 => 4.0
string vs. string	string	\"ab\".add.\"c\" => \"abc\"
integer vs. string	string	3.add.\"ab\" => \"3ab\"
real vs. string	string	\"ab\".add.3.5 => \"ab3.5\"
.sub.	integer vs. integer	integer	2.sub.2 => 0
real vs. real	real	2.0.sub.2.0 => 0.0
real vs. integer	real	2.0.sub.2 => 0.0
.mul.	integer vs. integer	integer	2.mul.2 => 4
real vs. real	real	2.0.mul.2.0 => 4.0
real vs. integer	real	2.0.mul.2 => 4.0
.div.	integer vs. integer	integer	2.div.2 => 1
real vs. real	real	2.0.div.2.0 => 1.0
real vs. integer	real	2.0.div.2 => 1.0

The following table describes the associative and precedence of the logical, relational, and arithmetic operators:

Operator	Associative	Precedence (low to high)
.or.	left to right	1
.and.	left to right	2
.not.	right to left	3
.eq. .ne.	left to right	4
.lt. .le. .gt. .ge.	left to right	5
.add. .sub.	left to right	6
.mul. .div.	left to right	7

The two operands of a relational operator will be:

• integer vs. integer
• real vs. real
• real vs. integer
• string vs. string

The interpreter must read from a file the instructions of a program written inLAO. In case of an error in an instruction, the interpreter must stop and show:

• the line number of the instruction that provoked the error
• the instruction that provoked the error
• the type of instruction that provoked the error, what is the error, and possible solution (the interpreter must only show unknown statement if the instruction does not match the beginning of any valid statement in the languageLAO)

Sample program inLAOlanguage:

w = \"HOLA\"

y = \" MUNDO\"

if 3 .gt. 2 then a = 2 .add. 1 .add. 3 .mul. 4

z = w .add. y

print z

print

print

if z .eq. \"HOLA MUNDO\" then print z

cc = 0

c2 = 9

c = 4

print

print

if c .eq. 4 then a = c .add. 3 .div. 3

n = 3.0 .add. 2 .mul. c

print \"n = \"

print n

print

print

a = 3 .mul. c .add. 2

print \"a = \"

print a

print

print

print \"ENTER AN INTEGER NUMBER: \"

read b

print

print

print \"YOU ENTERED: \"

print b

print

print

print

if b .gt. 7 .and. b .le. 9 .or. b .eq. 8 then print \"a = \"

if b .gt. 7 .and. b .le. 9 .or. b .eq. 8 then print a

print

print

end.