Harpo Final Project

. . . a swell compiler for a very restricted grammar:

Example test cases

Source code:

(machine code and abstract syntax tree can be found at the end)

GRAMMAR:

    
Program         ::== Statement $
Statement       ::== print ( Expr )
                ::== Id = Expr
                ::== VarDecl
                ::== if BoolExpr Statement
                ::== while BoolExpr Statement
                ::== { StatementList }
StatementList   ::== Statement StatementList
                ::== ?
Expr            ::== IntExpr
                ::== CharExpr
                ::== BoolExpr
                ::== Id
IntExpr         ::== digit op Expr
                ::== digit
CharExpr        ::== " CharList "
CharList        ::== Char CharList
                ::== Space CharList
                ::== ?
BoolExpr        ::== ( digit boolOp Expr )
                ::== ( boolInstance boolOp Expr )
                ::== boolInstance
VarDecl         ::== Type Id
Type            ::== int | char | bool
Id              ::== Char
Char            ::== a | b | c ... z
Space           ::== the space character
digit           ::== 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0
op              ::== + | -
boolInstance    ::== true | false
boolOp          ::== == | !=

NOTES:

Comments: All comments must be preceded by and followed by the # symbol. Other than this requirement they can appear anywhere in the source code, even bisecting tokens.

Booleans: Except for `true` or `false` on their own, boolean expressions must be surrounded by parentheses, even if these would already be there in a print statement. For example: print(1!=2) returns an error. print ((1!=2)) is correct. In boolean expressions, the integer 1 evaluates to true, 0 evaluates to false, and all other integers do not evaluate to a boolean value when compared to a boolean (hence ((2 == false) || (2 == true)) returns false). Integers can, however, be compared to each other. Strings cannot be used in boolean expressions - this will return an error. In the machine code our compiler generates, printing booleans will print 1 if true, 0 if false.

Integers are allocated one byte so an integer can be from 0-255. Integers must be positive. Strings (CharLists) can be of any length, except that the entire program must be 128 bytes or less.