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1.6

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Arrays

Array types represent maps from an interval [0,end) of a type "domain" to a type "range". An array type thing.t can be created like this:

instance thing : array(domain.t,range.t)

The implementation of this type requires that domain.t be interpreted as 'int'.

module array(domain,range) = {

    type t
return an empty array

    action empty returns (a:t)
return an array with end=s and all values mapped to y 
    action create(s:domain,y:range) returns (a:t)
mutate an array a so that x in [0,end) maps to y 
    action set(a:t,x:domain,y:range) returns (a:t)
get the value y such that x in [0,end) maps to y in array a 
    action get(a:t,x:domain) returns (y:range)
get the value of end 
    action size(a:t) returns (s:domain)
change the size of the array 
    action resize(a:t,s:domain,v:range) returns (a:t)
add one element to the array 
    action append(a:t,v:range) returns (a:t)

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Representation

Function "end" gives the end value of an array while value(a,x) gives the value that x maps to in a.

    function end(A:t) : domain
    function value(A:t,X:domain) : range
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Specification

Notice that get and set have the precondition that x is in [0,end).

    object spec = {
    property end(X) >= 0

    after empty {
        assert end(a) = 0
    }
    before create {
        assert 0 <= s
    }
    after create {
        assert end(a) = s & value(a,X) = y
    }
        before set {
        assert 0 <= x & x < end(a)
    }
    after set {
            assert end(a) = end(old a);
        assert value(a,X) = y if X = x else value(old a,X)
    }
    before get {
        assert 0 <= x & x < end(a)
    }
    after get {
        assert value(a,x) = y
    }
    after size {
        assert s = end(a)
    }
    after resize {
        assert end(a) = s;
        assert 0 <= X & X < end(old a) -> value(a,X) = value(old a,X);
        assert end(old a) <= X & X < s -> value(a,X) = v
    }
    after append {
        assert end(a) > end(old a) & ~(end(old a) < X & X < end(a));
        assert 0 <= X & X < end(old a) -> value(a,X) = value(old a,X);
        assert value(a,end(old a)) = v
    }
    }

    object impl = {
object t_ = {}

<<< member class t_ : std::vector<range> {};

interpret t -> <<< t_ >>>

    interpret t -> <<< std::vector<`range`> >>>

    definition value(a:t,i:domain) = <<< (0 <= `i` && `i` < `a`.size()) ? `a`[`i`] : val >>>

    definition end(a:t) = <<< `a`.size() >>>

    implement create {
        <<<
            `a`.resize(`s`);
            for (unsigned i = 0; i < `s`; i++)
                `a`[i] = y;
        >>>
    }

    implement empty {
        <<<
        >>>
    }

    implement set {
        <<<
            if (0 <= `x` && `x` < (`domain`)`a`.size())
                `a`[`x`] = `y`;
        >>>
    }

    implement get {
        <<<
            if (0 <= `x` && `x` < (`domain`)`a`.size())
                `y` = `a`[`x`];
        >>>
    }

    implement size {
        <<<
            `s` = (`domain`) `a`.size();
        >>>
    }

    implement resize {
        <<<
            unsigned __old_size = `a`.size();
            `a`.resize(`s`);
            for (unsigned i = __old_size; i < (unsigned)`s`; i++)
                `a`[i] = v;
            >>>
        }

    implement append {
        <<<
            `a`.push_back(`v`);
            >>>
        }

    <<< impl
        std::ostream &operator <<(std::ostream &s, const `t` &a) {
            s << '[';
        for (unsigned i = 0; i < a.size(); i++) {
            if (i != 0)
                s << ',';
            s << a[i];
        }
            s << ']';
        return s;
            }

        template <>
        `t` _arg<`t`>(std::vector<ivy_value> &args, unsigned idx, long long bound) {
            ivy_value &arg = args[idx];
            if (arg.atom.size())
                throw out_of_bounds(idx);
            `t` a;
            a.resize(arg.fields.size());
        for (unsigned i = 0; i < a.size(); i++) {
            a[i] = _arg<`range`>(arg.fields,i,0);
            }
            return a;
        }

        template <>
        void __deser<`t`>(ivy_deser &inp, `t` &res) {
            inp.open_list();
            while(inp.open_list_elem()) {
            res.resize(res.size()+1);
                __deser(inp,res.back());
            inp.close_list_elem();
                }
        inp.close_list();
        }

        template <>
        void __ser<`t`>(ivy_ser &res, const `t` &inp) {
            int sz = inp.size();
            res.open_list(sz);
            for (unsigned i = 0; i < (unsigned)sz; i++) {
            res.open_list_elem();
                __ser(res,inp[i]);
            res.close_list_elem();
                }
            res.close_list();
        }
ifdef Z3PP_H_ 
        template <>
            z3::expr __to_solver(gen& g, const z3::expr& z3val, `t`& val) {
            z3::expr z3end = g.apply("`end`",z3val);
            z3::expr __ret = z3end  == g.int_to_z3(z3end.get_sort(),val.size());
            unsigned __sz = val.size();
            for (unsigned __i = 0; __i < __sz; ++__i)
            __ret = __ret && __to_solver(g,g.apply("`value`",z3val,g.int_to_z3(g.sort("`domain`"),__i)),val[__i]);
                return __ret;
            }

        template <>
        void  __from_solver<`t`>( gen &g, const  z3::expr &v,`t` &res){
            `domain` __end;
            __from_solver(g,g.apply("`end`",v),__end);
            unsigned __sz = (unsigned) __end;
            res.resize(__sz);
            for (unsigned __i = 0; __i < __sz; ++__i)
            __from_solver(g,g.apply("`value`",v,g.int_to_z3(g.sort("`domain`"),__i)),res[__i]);
        }

        template <>
        void  __randomize<`t`>( gen &g, const  z3::expr &v, const std::string &sort_name){
            unsigned __sz = rand() % 4;
                z3::expr val_expr = g.int_to_z3(g.sort("`domain`"),__sz);
                z3::expr pred =  g.apply("`end`",v) == val_expr;
                g.add_alit(pred);
            for (unsigned __i = 0; __i < __sz; ++__i)
                __randomize<`range`>(g,g.apply("`value`",v,g.int_to_z3(g.sort("`domain`"),__i)),"`range`");
        }
endif

    >>>
    }

    trusted isolate iso = spec,impl

    attribute test = impl
}
¤

Option types

An option is either empty or has value or type range_t.

module option(range_t) = {

    type domain_t

    instantiate array(domain_t,range_t)
True if the option is empty 
    derived is_empty(X:t) = (end(X) = 0)
If not empty, gives the value 
    derived contents(X:t) = value(X,0)

    action just(inp:range_t) returns(out:t) = {
        out := create(1,inp);
    }

    interpret domain_t -> bv[1]
}

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Null number types

A Null number type is one that has a special value representing "not a number". The "not a number" value is encoded as the constant null_value.

module null_type(range_t,null_value) = {

    type t = struct {
        is_null : bool,
    contents : range_t
    }

    <<< encode `t`

    std::ostream &operator <<(std::ostream &s, const `t` &a) {
        if (a.is_null)
            s << "`null_value`";
        else
            s << a.contents;
        return s;
    }

    template <>
    `t` _arg<`t`>(std::vector<ivy_value> &args, unsigned idx, long long bound) {
        ivy_value &arg = args[idx];
        if (arg.fields.size())
        throw out_of_bounds(idx);
        `t` a;
        a.is_null = (arg.atom == "`null_value`");
        a.contents = _arg<`range_t`>(args,idx,bound);
        return a;
    }

    template <>
    void  __ser<`t`>(ivy_ser &res, const `t` &t){
        if (t.is_null)
            res.set((long long)strtoull("`null_value`",NULL,0));
        else
            __ser(res,t.contents);
    }

    template <>
    void __deser<`t`>(ivy_deser &inp, `t` &res){
        long long val;
        inp.get(val);
        res.is_null = (val == (long long)strtoull("`null_value`",NULL,0));
        std::vector<ivy_value> args;
        args.resize(1);
        std::ostringstream sts;
        sts << val;
        args[0].atom = sts.str();
        res.contents = _arg<`range_t`>(args,0,0);
        }
    >>>
}
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Paths

A path is similar to an array but differs in the way it is serialized. That is, a path with elements e_0, e_1, ... is serialized as a string of the form "e_0/e_1/...". To prevent misinterpretation, a separator character '/' is replaced by '\/' and '\' by '\'. Also, string quatation marks '"' are elided from e_0, e_1 ... A further difference between paths and strings is that paths are extensional -- if two paths have the same sequence of elements, they are equal. This means that to stay decidable, the index type of paths must be finite.

A path type thing.t can be created like this:

instance thing : path(domain.t,range.t)

The implementation of this type requires that domain.t be interpreted as an integer type.

module path(domain,range) = {

    type t
return an empty array

    action empty returns (a:t)
return an array with end=s and all values mapped to y 
    action create(s:domain,y:range) returns (a:t)
mutate an array a so that x in [0,end) maps to y 
    action set(a:t,x:domain,y:range) returns (a:t)
get the value y such that x in [0,end) maps to y in array a 
    action get(a:t,x:domain) returns (y:range)
get the value of end 
    action size(a:t) returns (s:domain)
change the size of the array 
    action resize(a:t,s:domain,v:range) returns (a:t)
add one element to the array 
    action append(a:t,v:range) returns (a:t)

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Representation

Function "end" gives the end value of an array while value(a,x) gives the value that x maps to in a.

    function end(A:t) : domain
    function value(A:t,X:domain) : range
¤

Specification

Notice that get and set have the precondition that x is in [0,end).

    property [extensionality]
       forall X,Y. (end(X) = end(Y))
                   & (forall I. (I < end(X) -> value(X,I) = value(Y,I)))
                   -> X = Y

    object spec = {
    property end(X) >= 0

    after empty {
        assert end(a) = 0
    }
    before create {
        assert 0 <= s
    }
    after create {
        assert end(a) = s & value(a,X) = y
    }
        before set {
        assert 0 <= x & x < end(a)
    }
    after set {
        assert value(a,X) = y if X = x else value(old a,X)
    }
    before get {
        assert 0 <= x & x < end(a)
    }
    after get {
        assert value(a,x) = y
    }
    after size {
        assert s = end(a)
    }
    after resize {
        assert end(a) = s;
        assert 0 <= X & X < end(old a) -> value(a,X) = value(old a,X);
        assert end(old a) <= X & X < s -> value(a,X) = v
    }
    after append {
        assert end(a) > end(old a) & ~(end(old a) < X & X < end(a));
        assert 0 <= X & X < end(old a) -> value(a,X) = value(old a,X);
        assert value(a,end(old a)) = v
    }
    }

    object impl = {
object t_ = {}

<<< member class t_ : std::vector<range> {};

interpret t -> <<< t_ >>>

    interpret t -> <<< std::vector<`range`> >>>

    definition value(a:t,i:domain) = <<< (0 <= `i` && `i` < `a`.size()) ? `a`[`i`] : val >>>

    definition end(a:t) = <<< `a`.size() >>>

    implement create {
        <<<
            `a`.resize(`s`);
            for (unsigned i = 0; i < `s`; i++)
                `a`[i] = y;
        >>>
    }

    implement empty {
        <<<
        >>>
    }

    implement set {
        <<<
            if (0 <= `x` && `x` < (`domain`)`a`.size())
                `a`[`x`] = `y`;
        >>>
    }

    implement get {
        <<<
            if (0 <= `x` && `x` < (`domain`)`a`.size())
                `y` = `a`[`x`];
        >>>
    }

    implement size {
        <<<
            `s` = (`domain`) `a`.size();
        >>>
    }

    implement resize {
        <<<
            unsigned __old_size = `a`.size();
            `a`.resize(`s`);
            for (unsigned i = __old_size; i < (unsigned)`s`; i++)
                `a`[i] = v;
            >>>
        }

    implement append {
        <<<
            `a`.push_back(`v`);
            >>>
        }

    <<< impl
        std::ostream &operator <<(std::ostream &s, const `t` &a) {
            s << '\"';
        for (unsigned i = 0; i < a.size(); i++) {
            if (i != 0)
                s << '/';
            std::ostringstream os;
            os << a[i];
            std::string st = os.str();
            for (unsigned j = 0; j < st.size(); j++) {
                char c = st[j];
            if (c == '/')
                s << "\\/";
            else if (c == '\\')
                s << "\\\\";
            else if (c != '\"')
                s << c;
            }
        }
            s << '\"';
        return s;
            }

        template <>
        `t` _arg<`t`>(std::vector<ivy_value> &args, unsigned idx, long long bound) {
            ivy_value &arg = args[idx];
            if (arg.fields.size())
                throw out_of_bounds(idx);
            `t` a;
        ivy_value tmp;
        tmp.fields.resize(1);
        std::string str = arg.atom;
        for (unsigned i = 0; i < str.size(); i++) {
            char c = str[i];
            if (c == '\\' && i+1 < str.size())
                    tmp.fields.back().atom.push_back(str[++i]);
                    else if (c == '/')
                tmp.fields.resize(tmp.fields.size()+1);
            else if (c != '\"')
                        tmp.fields.back().atom.push_back(c);
                }
            a.resize(tmp.fields.size());
        for (unsigned i = 0; i < a.size(); i++) {
            a[i] = _arg<`range`>(tmp.fields,i,0);
            }
            return a;
        }

        template <>
        void __deser<`t`>(ivy_deser &inp, `t` &res) {
            inp.open_list();
            while(inp.open_list_elem()) {
            res.resize(res.size()+1);
                __deser(inp,res.back());
            inp.close_list_elem();
                }
        inp.close_list();
        }

        template <>
        void __ser<`t`>(ivy_ser &res, const `t` &inp) {
            int sz = inp.size();
            res.open_list(sz);
            for (unsigned i = 0; i < (unsigned)sz; i++) {
            res.open_list_elem();
                __ser(res,inp[i]);
            res.close_list_elem();
                }
            res.close_list();
        }
ifdef Z3PP_H_ 
        template <>
            z3::expr __to_solver(gen& g, const z3::expr& z3val, `t`& val) {
            z3::expr z3end = g.apply("`end`",z3val);
            z3::expr cond = z3end  == g.int_to_z3(z3end.get_sort(),val.size());
            for (unsigned i = 0; i < val.size(); i++)
            cond = cond && __to_solver(g,g.apply("`value`",z3val,g.int_to_z3(g.sort("`domain`"),i)),val[i]);
            return cond;
            }

        template <>
        void  __from_solver<`t`>( gen &g, const  z3::expr &v,`t` &res){
            `domain` __end;
            __from_solver(g,g.apply("`end`",v),__end);
            unsigned __sz = (unsigned) __end;
            res.resize(__sz);
            for (unsigned __i = 0; __i < __sz; ++__i)
            __from_solver(g,g.apply("`value`",v,g.int_to_z3(g.sort("`domain`"),__i)),res[__i]);
        }

        template <>
        void  __randomize<`t`>( gen &g, const  z3::expr &v, const std::string &sort_name){
            unsigned __sz = rand() % 4;
                z3::expr val_expr = g.int_to_z3(g.sort("`domain`"),__sz);
                z3::expr pred =  g.apply("`end`",v) == val_expr;
                g.add_alit(pred);
            for (unsigned __i = 0; __i < __sz; ++__i)
                __randomize<`range`>(g,g.apply("`value`",v,g.int_to_z3(g.sort("`domain`"),__i)),"`range`");
        }
endif

    >>>
    }

    trusted isolate iso = spec,impl
}
¤

Maps.

This module provides a relational model of a function from a type dom to a type rng. Initially, everything is mapped to the element zero.

The key invariant of a map is that it is a function, i.e., for every X there exists a Y such that map(X,Y). The module does not state this invariant, however, since the quantifier alternation could destroy stratification. Instead it provides a "lemma" that allows the user to instantiate Y for particular values of X.

Parameters:

dom The domain type rng The range type zero The initial value for every domain element

module map(dom,rng,zero) = {

    relation map(X:dom,Y:rng)

    action set_(x:dom,y:rng)
get the value of x 
    action get(x:dom) returns (y:rng)
prove there exists a value for x 
    action lemma(x:dom)

    object spec = {
    init map(X,Y) <-> Y = zero

    implement set_(x:dom,y:rng) {
        call lemma(x);
        map(x,Y) := Y = y
    }
    implement get(x:dom) returns (y:rng) {
        assume map(x,y)
    }
    implement lemma(x:dom) {
        assume exists Y. map(x,Y)
    }
    }
    conjecture map(K,L) & map(K,M) -> L = M
}

¤

Partial functions

This module represents a mutable partial function type dom to type rng. The state consists of relation map that stores the function as a set of tuples, and an auxiliary set pre that gives the pre-image.

¤

module partial_function(dom,rng) = {

    relation map(X:dom,Y:rng)
    relation pre(X:dom)
mutate the function so x maps to y 
    action remap(x:dom,y:rng)
remove an element from the pre-image 
    action remove(x:dom)
get the value of x, if any 
    action get(x:dom) returns (y:rng)
true if x is in the pre-image 
    action present(x:dom) returns (r:bool)
if x in pre, there exists a y such that map(x,y) 
    action lemma(x:dom)

    object spec = {
    init ~map(X,Y)

    implement remap {
        call lemma(x);
        map(x,Y) := Y = y;
        pre(x) := true
    }

    implement remove {
        call lemma(x);
        map(x,Y) := false;
        pre(x) := false
    }

    after get {
        assume pre(x) -> map(x,y)
    }

    after present {
        assume r = pre(x)
    }

    implement lemma(x:dom) {
        assume pre(x) -> exists Y. map(x,Y)
    }
    }

    conjecture map(K,L) & map(K,M) -> L = M

}

¤

Witness

This is similar to partial_function, but has no domain. Useful for storing a witness to an existential quantifier without creating a function cycle.

¤

module witness(rng) = {

    action set(v:rng)

    action get returns (v:rng)

    action is_empty returns (r:bool)

    action clear

    relation is(Y:rng)

    relation present

    object spec = {

    after init {
        is(Y) := false;
        present := false
    }

    after set {
        is(Y) := Y = v;
        present := true
    }

    after get {
        assert present -> is(v)
    }

    after clear {
        is(Y) := false;
        present := false
    }

    after is_empty {
        assert r <-> ~present
    }
    }

    object impl = {
    relation full
    individual val : rng

    after init {
        full := false
    }

    implement set {
        val := v;
        full := true
    }
    implement get {
        v := val
    }
    implement clear {
        full := false
    }
    implement is_empty {
        r := ~full
    }

    conjecture (present <-> full) & (full -> is(val))
    }

    isolate iso = this

    attribute test = impl
}
This module makes a relation functional, meaning that it is total and injective.

module functional(rel) = {
    property [totality] exists Y. rel(X,Y)
    property [injectivity] rel(X,Y) & rel(X,Z) -> Y = Z
}
This module makes a relation inverse functional, meaning that its transpose is total and injective.

module inverse_functional(rel) = {
    property [totality] exists Y. rel(Y,X)
    property [injectivity] rel(Y,X) & rel(Z,X) -> Y = Z
}

module set_wrapper(key) = {

    object s = {}

    <<< header
include 
    >>>

    <<< member
    std::set<`key`> `s`;
    >>>

    <<< init
        `s`.insert(0);
    >>>

    implement insert(x:key) {
    <<<
        `s`.insert(`x`);
    >>>
    }

    implement erase(lo:key,hi:key) {
    <<<
            `s`.erase(`s`.lower_bound(`lo`),`s`.upper_bound(`hi`));
    >>>
    }

    implement get_glb(k:key) returns (res:key) {
    <<<
            `res` = *(--`s`.upper_bound(`k`));
    >>>

    }


}

¤

Ordered set representation

This is intended to be implemented using the STL set template.

Ordered sets assume the element type has a total non-strict order, with a least element 0. They provide insertion of elements (in log time), deletion of ranges (in n log(n) time) and finding greatest lower bounds (log n).

For help with proofs, this module also provides an auxiliary map "succ" that gives the successor of every element in the set. The "successor" of the maximal element in the set is 0.

module ordered_set(key) = {

    action insert(nkey:key)
    action erase(lo:key,hi:key)
    action get_glb(k:key) returns (res:key)

    relation s(K:key)

    instantiate succ : map(key,key,0) # ghost

    object spec = {
    init s(K) <-> K = 0
insert one element 
    before insert {
        s(nkey) := true;
following is ghost code to update the successor relation 
        local v:key {
        if some lub:key. ~(lub <= nkey) & s(lub) minimizing lub {
            v := lub
        }
        else {
            v := 0
        };
        call succ.set_(nkey,v)
        };
        if some glb:key. ~(nkey <= glb) & s(glb) maximizing glb {
        call succ.lemma(glb); # instantiate succ(glb)
        call succ.set_(glb,nkey)
        }
    }
erase elements in a closed interval 
    before erase {
        s(K) := s(K) & ~(lo <= K & K <= hi)
    }
the the greatest element <= k 
    after get_glb {
        if some glb:key. glb <= k & s(glb) maximizing glb {
        call succ.lemma(glb); # instantiate succ(glb)
        assume res = glb
        }
    }
    }
Useful invariants of the "succ" relation. The successor of K is also in the set, and nothing between K and its successor is in the set. Here, if L = 0 it means K is the maximim element, so we have to treat this as a special case.

    conjecture s(K) & succ.map(K,L) & L ~= 0 -> ~(L <= K) & s(L)
    conjecture s(K) & succ.map(K,L) & ~(M <= K) & (L = 0 | ~(L <= M)) -> ~s(M)

    instance impl : set_wrapper(key)

}

module map_wrapper(key,value) = {

    object s = {}

    <<< header
include 
    >>>

    <<< member
    std::map<`key.t`,`value`> `s`;
    >>>

    <<< init
    >>>

    implement set(x:key.t,y:value) {
    <<<
        `s`[`x`] = `y`;
    >>>
    }

    implement get(x:key.t,def:value) returns (y:value) {
    <<<
        std::map<`key.t`,`value`>::iterator it = `s`.find(`x`);
        if (it == `s`.end()) {
            `y` = `def`;
        } else {
            `y` = it->second;
        }
    >>>
    }

    implement erase(lo:key.iter.t,hi:key.iter.t) {
    <<<


        if (!`lo`.is_end && (`hi`.is_end || `lo`.val < `hi`.val))
              `s`.erase(`lo`.is_end ? `s`.end() : `s`.lower_bound(`lo`.val),
                    `hi`.is_end ? `s`.end() : `s`.lower_bound(`hi`.val));

    >>>
    }
implement begin(k:key.t) returns (res:key.iter.t) { <<< std::map<key.t,value>::iterator __it = s.lower_bound(k); if (__it == s.end()) { res.is_end = true; res.val = 0; } else { res.is_end = false; res.val = __it->first; } >>>

}

    implement lub(it:key.iter.t) returns (res:key.iter.t) {
    <<<
        if (`it`.is_end) {
            `res`.is_end = true;
            `res`.val = 0;
        } else {
        std::map<`key.t`,`value`>::iterator __it = `s`.lower_bound(`it`.val);
        if (__it == `s`.end()) {
            `res`.is_end = true;
            `res`.val = 0;
        } else {
            `res`.is_end = false;
            `res`.val = __it->first;
        }
        }
    >>>

    }

    implement glb(it:key.iter.t) returns (res:key.iter.t) {
    <<<
        std::map<`key.t`,`value`>::iterator __it = `it`.is_end ? `s`.end() : `s`.upper_bound(`it`.val);
        `res`.is_end = false;
            `res`.val = (--__it)->first;
    >>>

    }

    implement next(inp:key.iter.t) returns (res:key.iter.t) {
    <<<
        std::map<`key.t`,`value`>::iterator __it = `s`.upper_bound(`inp`.val);
        if (__it == `s`.end()) {
            `res`.is_end = true;
            `res`.val = 0;
        } else {
                `res`.is_end = false;
            `res`.val = __it->first;
        }
    >>>
    }

    action show = {
    <<<
            std::cout << "{";
        for(std::map<`key.t`,`value`>::iterator __it = `s`.begin(), __en = `s`.end(); __it != __en; ++__it)
            std::cout << __it->first << ":" << __it->second << ",";
            std::cout << "}" << std::endl;
    >>>

    }
}
¤

Ordered map representation

This is intended to be implemented using the STL map template.

Ordered maps assume the key type has a total non-strict order, with a least element 0 and iteration. They provide insertion of key/value pairs (in log time), deletion of ranges of keys (in n log(n) time) and iteration.

For help with proofs, this module also provides an auxiliary map "succ" that gives the successor of every element in the map. The "successor" of the maximal element in the map is 0.

module ordered_map(key,value) = {
set the value of key k 
    action set(nkey:key.t,v:value)
is the key present in the map? 
    action present(k:key.t) returns (ans:bool)
get the value of key k or zero 
    action get(k:key.t,def:value) returns (v:value)
remove all leys in range [lo,hi] 
    action erase(lo:key.iter.t,hi:key.iter.t)
get least iterator >= it 
    action lub(it:key.iter.t) returns (res:key.iter.t)
get least iterator >= it 
    action glb(it:key.iter.t) returns (res:key.iter.t)
iterator least key > iter or end 
    action next(it:key.iter.t) returns (res:key.iter.t)

    relation contains(K:key.t)
    relation maps(K:key.t,V:value)

    function gap(k:key.iter.t,m:key.iter.t) =
              forall L. ~(key.iter.ahead(L,k) & key.iter.done(L,m) & contains(L))

    object spec = {

    init ~contains(K) & ~maps(K,V)

    property gap(W,X) & gap(Y,Z) & Y < X -> gap(W,Z)
    property gap(W,X) & W <= Y & Z <= X -> gap(Y,Z)
    property gap(K,M) -> ~(key.iter.ahead(L,K) & key.iter.done(L,M) & contains(L))
insert one element 
    before set {
        contains(nkey) := true;
        maps(nkey,X) := X = v
    }


    after set {
        local it:key.iter.t {
        it := key.iter.create(nkey);
        assert gap(X,Y) <-> old gap(X,Y) & ~(X < it & it < Y)
        }
    }

    after get {
        assert maps(k,v) & contains(k) | ~contains(k) & v = def
    }
erase elements in a closed interval 
    before erase {
        contains(K) := contains(K) & ~key.iter.between(lo,K,hi);
        maps(K,V) := maps(K,V) & ~key.iter.between(lo,K,hi)
    }

    after erase {
        assert gap(X,Y) <-> (old gap(X,Y)
                             | old gap(X,lo) & old gap(hi,Y)
                                   & (Y < hi | key.iter.is_end(hi) | ~contains(key.iter.val(hi))))
    }

    after lub {
        assert it <= res;
        assert key.iter.between(it,X,res) -> ~contains(X);
        assert key.iter.is_end(res) | (contains(key.iter.val(res))
                                       & exists Y. maps(key.iter.val(res),Y))
assert succ(K,key.iter.val(res)) -> done(K,it) 
    }

    before glb {
        assert exists K. (~key.iter.ahead(K,it) & contains(K))
    }

    after glb {
        assert res <= it & contains(key.iter.val(res));
        assert exists U. (gap(res,U) & key.iter.between(res,key.iter.val(it),U))
    }

    before next {
        assert it < key.iter.end
    }

    after next {
        assert it < res & gap(it,res);
        assert key.iter.is_end(res) | contains(key.iter.val(res))
    }

    }
Useful invariants of the "succ" relation. The successor of K is also in the map, and nothing between K and its successor is in the map. Here, if L = 0 it means K is the maximim element, so we have to treat this as a special case.

conjecture contains(K) & succ.map(K,L) & L ~= 0 -> ~(L <= K) & contains(L) conjecture contains(K) & succ.map(K,L) & ~(M <= K) & (L = 0 | ~(L <= M)) -> ~contains(M)

Mapping relation R is injective

    conjecture maps(X,Y) & maps(X,Z) -> Y = Z
Maps implies contains

    conjecture maps(X,Y) -> contains(X)

    instance impl : map_wrapper(key,value)

    trusted isolate iso = impl,spec

}


module ordered_map_impl(key,value) = {
set the value of key k 
    action set(nkey:key.t,v:value)
is the key present in the map? 
    action present(k:key.t) returns (ans:bool)
get the value of key k or zero 
    action get(k:key.t,def:value) returns (v:value)
remove all leys in range [lo,hi] 
    action erase(lo:key.iter.t,hi:key.iter.t)
get least iterator >= it 
    action lub(it:key.iter.t) returns (res:key.iter.t)
get least iterator >= it 
    action glb(it:key.iter.t) returns (res:key.iter.t)
iterator least key > iter or end 
    action next(it:key.iter.t) returns (res:key.iter.t)

    instantiate map_wrapper(key,value)
}

¤

Key/value arrays

This modules implements arrays of key/value pairs. The keys are specified relationally so that one can write properties such as "for every key satisfying predicate p, there exists an element having that key". On the other hand, the values are specified funcitonally, so one can easily retreive the value associated to a particular key.

The parameters of this module are:

index : the index structure, as in "array" key : the key type data : the value type

The available methods are:

empty : returns an empty array end : returns the index one after the last element get_key : gets the key at an index get_value : gets the value at and index append_pair : appends a key/value pair

Typical code to look up the value of a key k in array a would be:

if some (i : index.t) a.key_at(i,k) { var v := a.value_at(i); ... use value v ... } else { ... k is not present ... }

module keyval(index,key,data) = {

    type t

    function end(A:t) : index.t
    relation key_at(A:t, I:index.t, X:key)
    function value_at(A:t, I:index.t) : data

    action empty returns (s:t)
    action get_key(s:t, i:index.t) returns (k:key)
    action get_value(s:t, i:index.t) returns (d:data)
    action append_pair(s:t, k:key, d:data) returns (s:t)

    object spec = {

        property key_at(A,I,X) -> 0 <= I & I < end(A)
        property key_at(A,I,X) & key_at(A,I,Y) -> X = Y
        property 0 <= end(A)

        after empty {
            assert s.end = 0 & ~key_at(s,I,X)
        }
        before get_key {
            assert 0 <= i & i < s.end
        }
        after get_key {
            assert key_at(s,i,k)
        }
        before get_value {
            assert 0 <= i & i < s.end
        }
        after get_value {
            assert value_at(s,i) = d
        }
        after append_pair {
            assert key_at(s,I,X) <-> key_at(old s,I,X) | I = end(old s) & X = k;
            assert key_at(old s,I,X) -> value_at(s,I) = value_at(old s,I);
            assert value_at(s,end(old s)) = d
        }
    }

    object impl = {

        type pair = struct {
            p_key : key,
            p_value : data
        }

        instance arr : array(index.t,pair)

        destructor repr(X:t) : arr.t

        definition end(A:t) = repr(A).end
        definition value_at(A,I) = repr(A).value(I).p_value
        definition key_at(A,I,X) = (0 <= I & I < end(A) & repr(A).value(I).p_key = X)

        implement empty {
            repr(s) := arr.empty
        }
        implement get_key {
            k := repr(s).get(i).p_key
        }
        implement get_value {
            d := repr(s).get(i).p_value
        }
        implement append_pair {
            var p : pair;
            p.p_key := k;
            p.p_value := d;
            repr(s) := repr(s).append(p)
        }
    }
    isolate iso = this with index
}