####### DOCUMENTATIATOIAITAT ION ########


Files:
Typechecker.hs: Simple modification of the bnfc-generated Testsyntax which calls the type-checking functions.

Typecheck.hs: Contains the type-checking functions typeCheckExp, typeCheckVar and typeCheckStm and some utility functions, responsible for the entire type-checking process.

Abssyntax.hs, Parsyntax.y, Lexsyntax.x,ErrM.hs,Printsyntax.hs,Skelsyntax.hs: The files generated by bnfc, only modification is the removal of the Bool type in Abssyntx.hs so haskell's internal type can be used.


typing rules
++++++++++++


(t is little tau, T is large tau, E is 'in', and + is that other symbol)



[Eq, Neq]

e:bool  <=  e1:t  &  e2:t
where e is e1 Eq e2.


[Plus, Minus, Times, Div]

e:int  <=  e1:int  &  e2:int
where e is e1 Plus e2.


[Lt, ELt, Gt, EGt]

e:bool  <=  e1:int  &  e2:int
where e is e1 Lt e2.


[Assignment]

T+ i := e:t  <=  i:t E T  &  T+ e:t
where the assignment is identifier i = expression e.


[ExpT]

u,e:t  <=  e:t  &  u:t
where the expression is type u expression e.


[ENeg]

e:int  <=  e:int


[ENot]

e:bool  <=  e:bool


[SExp, SBlock]

S:NoType  <=  e:t


[SIf]

T+ if e then s1 else s2  <=  T+ e:bool  &  T+ s1  &  T+ s2


[SWhile]

T+ while e do s  <=  T+ e:bool  &  T+ s


[SDecl]

T+ i:t => T', i:t  <=  i!ET  &  e:t  &  u:t

(Type u Ident i = Exp e)