EXPInterpreter

Description

This Scala programm can interpret any EXP programm.

Usage

Compile and run the project with maven.

EXP

EXP is a custom, turing complete programming language, which is used by the Software Paradigms course at the TU Graz.

Supported variables and functions

Following built-in variables are supported:

• integer
• string
• list

Following built-in functions are supported:

• plus(x,y) (x+y)
• minus(x,y) (x-y)
• mult(x,y) (x*y)
• div(x,y) (x/y)
• first(x) (first element in list x or first char in string x)
• rest(x) (all elements in list x except the first one)
• build(x,y) (put element x in list y)
• inc(x) (increase x by one)
• dec(x) (decrease x by one)
• reverse(x) (returns list/string x in reverse order)
• len(x) (returns the length of list/string x as an integer)
• fak(x) (returns factorial of x)
• sqrt(x) (returns the square root of x, floors if necessary)
• abs(x) (returns the absolute value of x)
• random(x) (returns a random number between 0 and x)
• gcd(x,y) (returns the greatest common divisor of x and y)
• pow(x,y) (returns x^y)

Following built-in conditionals are supported (all conditionals support lists and integers):

• eq?(x,y) (true if x and y have the same value)
• lt?(x,y) (true if x < y)
• gt?(x,y) (true if x > y)
• is0?(x) (true if x = 0)
• is1?(x) (true if x = 1)
• atom?(x) (true if x is an integer/string, false if x is a list)
• ne?(x,y) (true if x == y * -1)

User defined functions and exceptions are also supported. Built-in functions can be overloaded by user defined functions if they have the same name. In this case, always the user defined function will be used.

Following built-in constant values are provided:

• INTMIN (Minimum integer value)
• INTMAX (Maximum integer value)

User defined variables automatically override constants if they hav the same name

Examples

Basic example:

{}
if eq?([1],build(1,[])) then plus(2, mult(3,4)) else div(4,2)

User defined function:

{concat(xs, ys) = if eq?(xs,[]) then ys else build(first(xs), concat(rest(xs),ys))}

Programm with user defined functions and user defined exceptions:

{foo(a,b)= if eq?(a,b) then throw MyException else plus(a,b);
  bar(a) = try foo(1,1) catch {MyException : a ; _ : 7}
}
bar(5)

Programm for counting the elements in a list:

{len(x) = if eq?(x,[]) then 0 else plus(1, len(rest(x)))}
len([1,2,3])