rewrite.h

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#pragma once
 
#include <ranges>
 
#include "mim/world.h"
 
namespace mim {
 
/// Recurseivly rebuilds part of a program **into** the provided World w.r.t.\ Rewriter::map.
/// This World may be different than the World we started with.
class Rewriter {
public:
    Rewriter(World& world)
        : world_(world) {
        push(); // create root map
    }
 
    World& world() { return world_; }
 
    /// @name Stack of Maps
    ///@{
    void push() { old2news_.emplace_back(Def2Def{}); }
    void pop() { old2news_.pop_back(); }
 
    /// Map @p old_def to @p new_def and returns @p new_def.
    /// @returns `new_def`
    const Def* map(const Def* old_def, const Def* new_def) { return old2news_.back()[old_def] = new_def; }
 
    /// Lookup `old_def` by searching in reverse through the stack of maps.
    /// @returns `nullptr` if nothing was found.
    const Def* lookup(const Def* old_def) {
        for (const auto& old2new : old2news_ | std::views::reverse)
            if (auto i = old2new.find(old_def); i != old2new.end()) return i->second;
        return nullptr;
    }
 
    /// @name rewrite
    /// Recursively rewrite old Def%s.
    ///@{
    virtual const Def* rewrite(const Def*);
    virtual const Def* rewrite_imm(const Def*);
    virtual const Def* rewrite_mut(Def*);
 
    virtual const Def* rewrite_arr(const Arr* arr) { return rewrite_seq(arr); }
    virtual const Def* rewrite_pack(const Pack* pack) { return rewrite_seq(pack); }
    virtual const Def* rewrite_seq(const Seq*);
    virtual const Def* rewrite_extract(const Extract*);
    virtual const Def* rewrite_hole(Hole*);
    ///@}
 
private:
    World& world_;
    std::deque<Def2Def> old2news_;
};
 
class VarRewriter : public Rewriter {
public:
    VarRewriter(const Var* var, const Def* arg)
        : Rewriter(arg->world())
        , vars_(var ? Vars(var) : Vars()) {
        assert(var);
        map(var, arg);
    }
 
    const Def* rewrite_imm(const Def* imm) final {
        if (imm->local_vars().empty() && imm->local_muts().empty()) return imm; // safe to skip
        if (imm->has_dep(Dep::Hole) || vars_.has_intersection(imm->free_vars())) return Rewriter::rewrite_imm(imm);
        return imm;
    }
 
    const Def* rewrite_mut(Def* mut) final {
        if (vars_.has_intersection(mut->free_vars())) {
            if (auto var = mut->has_var()) vars_ = world().vars().insert(vars_, var);
            return Rewriter::rewrite_mut(mut);
        }
        return map(mut, mut);
    }
 
private:
    Vars vars_;
};
 
} // namespace mim