####### 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
++++++++++++


(v is used for values, e for expressions, s for statements, c is the context)


[Eq, NEq, Plus, Minus, Times, Div, Lt, ELt, Gt, EGt]

<e1 o e2,c> => <v,c''> <= <e1,c> => <v1,c'>  <e2,c'> => <v2,c''> v is the result of using operator o on v1 and v2


[Assignment]

<i := e,c> => c'[i -> v] <= <e,c> => <v,c'>

Assign the value v to i in the first scope i is found in.

[ENeg]

<e,c> => <-v,c'> <= <e,c> => <v,c'>


[ENot]

<e,c> => <not v,c'> <= <e,c> => <v,c'>

[EVar]

<i,c> => <c(i),c>

[EInt]

<n,c> => <n,c>

[EBool]

<b,c> => <b,c>

[EReadI,EReadB]

<c> => <v,c'> <= <IO,c> => <v,c'>

[EPost]

<i,c> => <v,c[i->v']> <= c(i) => v, v±1 => v'

Look up the variable, add/subtract 1 from the value then return the old value and context with modified value

[SExp]

<e,c> => c' <= <e,c> => <v,c'>

[SBlock]

<SBlock s,c> => c'''  <= push(c) => c' <s,c'> => c'' pop(c'') => c'''

Push a new scope onto the context, execute the statements in this context and the pop the scope from the context

[SEQ]

<s1;s2,c> => c'' <= <s1,c> => c' <s2,c'> => c''

[SIf]

<if e s1 s2,c> => pop(c''') <= <e,c> => <true,c'> push(c') <s1,c''> => c'''

<if e s1 s2,c> => pop(c''') <= <e,c> => <false,c'> push(c') <s2,c''> => c'''


[SWhile]

<while e s,c> => c' => <e,c> => <false,c'>

<while e s,c> => pop(c''') => <e,c> => <true,c'> push(c') => c'' <s,c''> => c'''


[SDecl]

<i := e,c> => c'[i->v] <= <e,c> => <v,c'>

Adds i with value v to the current scope in the context

[SDeclD]

<int i,c> => c[i->0]
<bool i,c> => c[i->false]

Adds i with default value in the current scope

[SNoop]

<SNoop,c> => c

SNoops does nothing so the same context is returned

[SPrint]

<e,c> => c'' <= <e,c> => <v,c'> <IO v,c'>  => c''