* Lambdas, applications, substitutions.
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3 changed files with 71 additions and 4 deletions
63
src/eval.cc
63
src/eval.cc
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@ -247,25 +247,72 @@ void evalArgs(ATermList args, ATermList & argsNF, Environment & env)
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env[name] = queryValuePath(parseHash(s));
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} else throw badTerm("invalid argument value", eVal);
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argsNF = ATappend(argsNF,
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argsNF = ATinsert(argsNF,
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ATmake("Tup(Str(<str>), <term>)", name.c_str(), eVal));
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args = ATgetNext(args);
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}
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argsNF = ATreverse(argsNF);
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}
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Expr substExpr(string x, Expr rep, Expr e)
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{
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char * s;
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Expr e2;
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if (ATmatch(e, "Var(<str>)", &s))
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if (x == s)
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return rep;
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else
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return e;
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if (ATmatch(e, "Lam(<str>, <term>)", &s, &e2))
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if (x == s)
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return e;
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/* !!! unfair substitutions */
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/* Generically substitute in subterms. */
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if (ATgetType(e) == AT_APPL) {
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AFun fun = ATgetAFun(e);
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int arity = ATgetArity(fun);
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ATermList args = ATempty;
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for (int i = arity - 1; i >= 0; i--)
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args = ATinsert(args, substExpr(x, rep, ATgetArgument(e, i)));
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return (ATerm) ATmakeApplList(fun, args);
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}
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if (ATgetType(e) == AT_LIST) {
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ATermList in = (ATermList) e;
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ATermList out = ATempty;
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while (!ATisEmpty(in)) {
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out = ATinsert(out, substExpr(x, rep, ATgetFirst(in)));
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in = ATgetNext(in);
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}
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return (ATerm) ATreverse(out);
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}
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throw badTerm("do not know how to substitute", e);
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}
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/* Evaluate an expression. */
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Expr evalValue(Expr e)
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{
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char * s;
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Expr eBuildPlatform, eProg, e2;
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Expr eBuildPlatform, eProg, e2, e3, e4;
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ATermList args;
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/* Normal forms. */
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if (ATmatch(e, "Str(<str>)", &s) ||
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ATmatch(e, "Bool(True)") ||
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ATmatch(e, "Bool(False)"))
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ATmatch(e, "Bool(False)") ||
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ATmatch(e, "Lam(<str>, <term>)", &s, &e2))
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return e;
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/* Value references. */
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@ -282,6 +329,14 @@ Expr evalValue(Expr e)
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return evalValue(e3);
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}
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/* Application. */
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if (ATmatch(e, "App(<term>, <term>)", &e2, &e3)) {
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e2 = evalValue(e2);
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if (!ATmatch(e2, "Lam(<str>, <term>)", &s, &e4))
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throw badTerm("expecting lambda", e2);
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return evalValue(substExpr(s, e3, e4));
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}
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/* Execution primitive. */
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if (ATmatch(e, "Exec(<term>, <term>, [<list>])",
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@ -60,6 +60,12 @@ using namespace std;
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makeArg(Arg(Str(nm), (Bool(True), _))) => (nm, "1")
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makeArg(Arg(Str(nm), (Bool(False), _))) => (nm, undef)
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subst(x, e1, e2) is defined as a generic topdown term
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traversal of e2, replacing each `Var(x)' with e1, and not
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descending into `Lam(x, _)'.
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Note: all stored expressions must be closed. !!! ugly
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getFile :: Hash -> FileName
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loadExpr :: Hash -> FileName
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hashExpr :: Expr -> Hash
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@ -76,6 +82,9 @@ Expr evalValue(Expr e);
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/* Return a canonical textual representation of an expression. */
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string printExpr(Expr e);
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/* Perform variable substitution. */
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Expr substExpr(string x, Expr rep, Expr e);
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/* Hash an expression. */
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Hash hashExpr(Expr e);
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@ -69,6 +69,9 @@ void runTests()
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evalTest(ATmake("Str(\"Hello World\")"));
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evalTest(ATmake("Bool(True)"));
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evalTest(ATmake("Bool(False)"));
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evalTest(ATmake("App(Lam(\"x\", Var(\"x\")), Str(\"Hello World\"))"));
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evalTest(ATmake("App(App(Lam(\"x\", Lam(\"y\", Var(\"x\"))), Str(\"Hello World\")), Str(\"Hallo Wereld\"))"));
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evalTest(ATmake("App(Lam(\"sys\", Lam(\"x\", [Var(\"x\"), Var(\"sys\")])), Str(\"i686-suse-linux\"))"));
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Hash builder1 = addValue("./test-builder-1.sh");
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