Simple Language

Programming language interpreter, similar to Scala subset

Description

A programming language interpreter developed in a Programming Paradigms class with Professor Cay Horstmann at SJSU. Simple Language is similar to Scala subset but differs in several ways:

• Only two types: integer and functions
• Defs end with semicolons
• Block has a single expression
• Function literals have syntax { ident, ident, ... => block }
• if fakes Boolean similar to C: > 0 is true, <= 0 is false

Grammar

block ::= (valdef | fundef)* expr
expr ::= expr2 | "if" "(" expr ")" block "else" block
expr2 ::= term (( "+" | "-" ) term)*
term ::= factor (( "*" | "/" ) factor)*
factor ::= wholeNumber | "(" expr ")" | ident | funcall | funliteral
funcall ::= ident "(" (expr ("," expr)*)? ")"
funliteral ::= "{" (ident ("," ident)*)? "=>" block "}"
valdef ::= "val" ident "=" expr ";"
fundef ::= "def" ident "=" funliteral ";" 

Examples

Simple addition and multiplication

val a = 1;
val b = 6;
a * a + b * b

Function literal

val max = { x, y => if (x - y) x else y };

Higher-order function

val twoTimes = { f, x => f(f(x)) }; 
twoTimes({x => x * x}, 2)

Recursion

def fac = { x => if (x) x * fac(x - 1) else 1 };

Curry

Multiplication

val multiply = { x => { y => x * y } } ;
multiply(3)(4)

Lists:

val list = 1 :: 2 :: Nil;
val y = isEmpty(list);
val x = head(1 :: Nil);

Credits

Cay Horstmann, SJSU