CMS Interpreter: Documentation and Applet

Syntax

<E> ::=

<C> |
<VAR> |
`[' <VN> `;' <NE> `;' <VE> `]' |
<E> `@' <E> |
reduct `{' <NN> `}' `|' <E> `|' `{' <NN> `}' |
freeze `{' <NN> `}' `(' <E> `)' |
<E> `.' <NAME> |
eval `(' <E> `)'

<C> ::=

<E>
fn <VAR> `=>' <C> |
<C> `(' <C> `)' |
if <C> then <C> else <C> |
let <VAR> '=' <C> in <C> |
<COP> |
<UNOP> <C> |
<C> <BINOP> <C>

<VN> ::=

[ <VAR> `->' <NAME> { `,' <VAR> `->' <NAME> } ]

<NE> ::=

[ <NAME> `->' <E> { `,' <NAME> `->' <E> } ]

<VE> ::=

[ <VAR> `->' <E> { `,' <VAR> `->' <E> } ]

<NN> ::=

[ <NAME> [ `->' <NAME> ] { `,' <NAME> [ `->' <NAME> ] } ]

<COP> ::=

<NUM> | false | true

<UOP> ::=

`-' | `!'

<BOP> ::=

`+' | `-' | `*' | `/' | `||' | `&&' | `==' | `!=' | `<' | `<=' | `>' | `>='

Remarks

<VAR> and <NAME> represent non empty sequences of letters and digits starting with a letter;
<NUM> represents rational numbers in the usual notation;
[ ] means optionality;
{ } means repetition (>= 0).
eval is the call-by-value effect-free version of doall of CMS_do (see Mixin Modules and Computational Effects ).

Semantics

See A Calculus of Module Systems (note that the syntax has been slightly changed!).

Examples

The factorial function

[ ; Fact -> fact; fact -> fn x => if x<=0 then 1 else x*fact(x-1)] . Fact (10)

A self-referential module

let m=[ ; M->self ; self -> [ ; X -> 1, Y -> self.X+1, Self -> self; ] ].M in m.Self.Y

Encoding of the lambda term ((lambda x . lambda y . x 7) 11)

freeze

Encoding a Counter object

[
value -> Val;
Val -> 0,
Inc-> reduct {Val -> Val } | self | {Inc -> Inc } @ [ ; Val -> value + 1; ];
self -> [
                value -> Val;
                Val -> 0,
                Inc -> reduct {Val -> Val } | self | {Inc -> Inc } @ [ ; Val -> value + 1; ];
               ]
]

Encoding the method invocation Counter.Inc.Val

freeze
   {Val->Val}
    (
      freeze

reduct