CSc 520. Language Prototyping III. The Language γ Examples. The Language γ... The Language γ. Principles of Programming Languages

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1 Slide 29 2 The Language γ Examples let fun f (v : t) = v + 3 prt f(5) let fun f (v : (t, t)) = fst v + snd v prt f((5, 6)) y let var x : t; fun f (v : t) = v + x x := 6; prt f(5) Copyright c 2003 C. Collberg Language Prototypg III Christian Collberg March 31, 2003 CSc 520 Prciples of Programmg Languages University of Arizona The Language γ... The Language γ We get the new grammar rules below. Slide 29 3 formal parameter ::= identifier : type formal parameter ::= value identifier : type formal parameter ::= result identifier : type declaration ::= fun identifier ( formal parameter ) = expression Slide 29 1 We are now gog to ext our language β from the previous lecture to clude functions and procedures. For simplicity we allow routes to take only one parameter. Multiple parameters can be simulated by passg pairs. Formal parameters can take two modes: value and result. factor ::= designator ( expression )

2 Slide 29 6 Static Semantics Function Calls The type of the actual argument has to match the type of the formal argument: sem_expression(fcall(f,e), RetType, Env) :- env_fd(f, (RetType,ArgType)/fun, Env), sem_expression(e, T, Env), sem_equivalent(t,argtype). Slide 29 4 A Prolog Parser for γ formal_parameter(formal(value, V, T)) --> identifier(v), [:], type(t). formal_parameter(formal(value, V, T)) --> [value], identifier(v), [:], type(t). formal_parameter(formal(result, V, T)) --> [result], identifier(v), [:], type(t). declaration(fun(f,p,e)) --> [fun], identifier(f), [ ( ], formal_parameter(p), [ ) ], [=], expression(e). factor(fcall(f,e)) --> designator(f), [ ( ], expression(e), [ ) ]. Dynamic Semantics Function Declarations Static Semantics Function Declarations Slide 29 7 We store with each function declaration the environment which it is declared. It is this environment the function will eventually execute. exec_declaration( fun(f,formal(m,v,t),e), Env1, Env2, Sto, Sto) :- exec_type(t, T1, Env1), env_bd(f, formal(m,v,t1)/e/env2/fun, Env1, Env2). Slide 29 5 In the abstract syntax a function declaration is represented as fun(funname,formal(mode,name,type),expression). sem_declaration(fun(f,formal(_,v,t),e), Env, Env2) :- sem_type(t, ArgType, Env), env_bd(v, ArgType/var, Env, Env1), sem_expression(e, RetType, Env1), env_bd(f, (RetType,ArgType)/fun, Env, Env2).

3 Slide % exec copy (formal(mode, name, type), comg environment, comg store,resultg store):- exec_copy_(formal(value,v,t),arg,env1,env2,sto1,sto4):- exec_expression(arg, ExprVal, Env1, Sto1, Sto2), store_allocate(loc, T, Sto2, Sto3), env_bd(v, Loc/T/var, Env1, Env2), store_update_variable(loc,exprval,sto3,sto4). exec_copy_(formal(result,v,t),_,env1,env2,sto1,sto2):- store_allocate(loc, T, Sto1, Sto2), env_bd(v, Loc/T/var, Env1, Env2). Slide 29 8 Dynamic Semantics Function Call We look up the function and the environment which it was declared. We transfer the actual argument to the formal argument. We execute the body. We transfer the formal argument back to the actual. exec_expression(fcall(fun,arg),retval,env,sto1,sto4):- env_fd(fun, Formal/Body/Env1/fun, Env), exec_copy_(formal, Arg, Env1, Env2, Sto1, Sto2), exec_expression(body, RetVal, Env2, Sto2, Sto3), exec_copy_out(formal, Arg, Env2, _, Sto3, Sto4). Dynamic Semantics Parameter Passg... A change to a value parameter does not affect the correspondg actual. Dynamic Semantics Parameter Passg A value parameter is passed by copyg its value to a temporary location. The comg environment is the one which the function will execute. Slide The current value of a formal result parameter is copied to the actual (which has to be a designator). % exec copy out(formal(mode, name, type), comg environment, Slide 29 9 For a result parameter we just allocate a location which will be used by the function when its body is evaluated. % exec copy (formal(mode, name, type), comg environment, comg store, resultg store) :- comg store, resultg store) :-

4 Slide Procedure Calls Syntax statement ::= designator ( expression ) declaration ::= proc identifier ( formal parameter ) = statements statement(pcall(f,e)) --> designator(f), [ ( ], expression(e), [ ) ]. declaration(proc(f,p,e)) --> [proc], identifier(f), [ ( ], formal_parameter(p), [ ) ], [=], statements(e), []. Slide % exec copy out(formal(mode, name, type), comg environment, comg store,resultg store):- exec_copy_out(formal(value,v,t),_,env,env,sto1,sto2):- env_fd(v, Loc/T/var, Env), store_deallocate(loc, Sto1, Sto2). exec_copy_out(formal(result,v,t),arg,env,env,sto1,sto4):- exec_designator(arg, LocA, Env, Sto1, Sto2), env_fd(v, LocV/T/var, Env), store_fetch_variable(locv, ValV, Sto1), store_update_variable(loca,valv,sto2,sto3), store_deallocate(locv, Sto3, Sto4). Slide Procedures Static Semantics In the abstract syntax a procedure declaration is represented as proc(procname,formal(mode,name,type),statement). sem_declaration(proc(f,formal(_,v,t),s), Env, Env2) :- sem_type(t, ArgType, Env), env_bd(v, ArgType/var, Env, Env1), sem_statement(s, Env1), env_bd(f, ArgType/proc, Env, Env2). Slide Procedure Calls Examples let proc f(v : t) = let var x : t x := 7; prt v + x; prtln f(5) sem_statement(pcall(f,e), Env) :- env_fd(f, ArgType/proc, Env), sem_expression(e, T, Env), sem_equivalent(t,argtype). let var x : t; proc f(v : t) = x := v x := 9; f(5); prt x; prtln

5 Procedure Calls Dynamic Semantics Slide exec_declaration( proc(f,formal(m,v,t),s),env1,env2,sto,sto):- exec_type(t, T1, Env1), env_bd(f, formal(m,v,t1)/s/env2/proc, Env1, Env2). exec_statement(pcall(proc,arg), Env, Sto1, Sto4) :- env_fd(proc, Formal/Body/Env1/proc, Env), exec_copy_(formal, Arg, Env1, Env2, Sto1, Sto2), exec_statement(body, Env2, Sto2, Sto3), exec_copy_out(formal, Arg, Env2, _, Sto3, Sto4). Readgs and References Slide Read Watts, pp