116 lines
4.3 KiB
C++
116 lines
4.3 KiB
C++
/** @file Expression.hpp
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*
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* Author: Roland Conybeare
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**/
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#pragma once
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#include "xo/reflect/TypeDescr.hpp"
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#include "xo/refcnt/Refcounted.hpp"
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#include "exprtype.hpp"
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#include <functional>
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#include <set>
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namespace xo {
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namespace ast {
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class Variable; /* see Variable.hpp */
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class Lambda; /* see Lamnbda.hpp */
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class Environment; /* see Environment.hpp */
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/** @class Expression
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* @brief abstract syntax tree for an EGAD program
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*
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* (Expression Graph with Automagic Derivation)
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*
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* Things you can do with an Expression:
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* - evaluate it using an interpreter
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* - execute it on a VM
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* - compile using LLVM
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* see xo-jit/
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*
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* Expressions are immutable. This means they can resused
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* across jit interactions
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*
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* Every expression evaluates to a value with a particular type
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**/
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class Expression : public ref::Refcount {
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public:
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using VisitFn = std::function
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<void (ref::brw<Expression>)>;
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using TransformFn = std::function
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<rp<Expression> (ref::brw<Expression>)>;
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using TypeDescr = xo::reflect::TypeDescr;
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public:
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explicit Expression(exprtype extype, TypeDescr valuetype)
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: extype_{extype}, valuetype_{valuetype}{}
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exprtype extype() const { return extype_; }
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TypeDescr valuetype() const { return valuetype_; }
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/** find free named variables in this expression.
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* comprises the set of names that don't match formal parameters in
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* enclosing lambdas.
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**/
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virtual std::set<std::string> get_free_variables() const = 0;
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/** visit each Expression node in this AST,
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* and invoke @p fn for each.
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* Returns the number of nodes visited.
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* Preorder: call @p fn for a node before visiting children
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**/
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virtual std::size_t visit_preorder(VisitFn visitor_fn) = 0;
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/** visit each Expression node in this AST,
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* including immediately-nested Lambda nodes;
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* but do not recurse into the params/body of such nested Lambdas.
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* Returns the number of nodes visited
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**/
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virtual std::size_t visit_layer(VisitFn visitor_fn) = 0;
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/** traverse ast @ref visit_preorder but do not visit Lambdas **/
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virtual rp<Expression> xform_layer(TransformFn visitor_fn) = 0;
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/** attach an environment to each lambda expression X in this subtree,
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* that will:
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* - resolve names matching X's arguments (formal parameters) to
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* from @p X.argv
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* - resolve free variables from @p parent
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**/
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virtual void attach_envs(ref::brw<Environment> parent) = 0;
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/** append to *p_set the set of free variables in this expression.
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* returns the number of free variables introduced
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*
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* @param env stack of lexcically-enclosing lamnbda expressions,
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* in nesting order, i.e. outermost first, innertmost last
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**/
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//virtual std::int32_t find_free_vars(std::vector<ref::brw<Lambda>> env) = 0;
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/** write human-readable representation to stream **/
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virtual void display(std::ostream & os) const = 0;
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/** human-readable string representation **/
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virtual std::string display_string() const;
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protected:
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/** useful when scaffolding expressions in a parser **/
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void assign_valuetype(TypeDescr x) { valuetype_ = x; }
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private:
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/** expression type (constant | apply | ..) for this expression **/
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exprtype extype_ = exprtype::invalid;
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/** type information (when available) for values produced by this
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* expression.
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**/
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TypeDescr valuetype_ = nullptr;
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}; /*Expression*/
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inline std::ostream &
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operator<<(std::ostream & os, const Expression & x) {
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x.display(os);
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return os;
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}
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} /*namespace ast*/
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} /*namespace xo*/
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/** end Expression.hpp **/
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