/*
* The parser needs to take concrete syntax, check to
* see that it is well formed, and produce abstract
* syntax. It provides the [[readtop]] function.
*
* At the top level, parsing amounts to looking for top
* level constructs and passing the rest of the work to
* [[parseexp]], which parses the input into [[Exp]]s.
* <parse.c>=
*/
static Def parse(Par p) {
switch (p->alt) {
case ATOM:
/*
* If we have a name, we treat it as an expression.
* <parse [[atom]] and return the result>=
*/
return mkExp(parseexp(p));
case LIST:
/*
* If we have a list, we need to look for [[define]],
* [[val]], and [[use]].
* <parse [[list]] and return the result>=
*/
{
Name first;
Parlist pl = p->u.list;
if (pl == NULL)
error("%p: empty list", p);
if (nthPL(pl, 0)->alt != ATOM)
error("%p: first item of list not name", p);
first = nthPL(pl, 0)->u.atom;
if (first == strtoname("define")) {
/*
* Parsing the top-level expressions requires checking
* the argument counts and then parsing the subpieces.
* For function definitions, we could check that formal
* parameters have distinct names, but that check is
* part of the operational semantics for function
* definition.
* <parse [[define]] and return the result>=
*/
if (lengthPL(pl) != 4 || nthPL(pl, 1)->alt != ATOM || nthPL(pl,
2)->alt != LIST)
error("%p: usage: (define fun (formals) body)", p);
{
Name name = nthPL(pl, 1)->u.atom;
Namelist formals = getnamelist(name, p, nthPL(pl, 2)->u.list);
Exp body = parseexp(nthPL(pl, 3));
return mkDefine(name, mkUserfun(formals, body));
}
}
if (first == strtoname("val")) {
/*
* <parse [[val]] and return the result>=
*/
Exp var, exp;
if (lengthPL(pl) != 3)
error("%p: usage: (val var exp)", p);
var = parseexp(nthPL(pl, 1));
if (var->alt != VAR)
error("%p: usage: (val var exp) (bad variable)", p);
exp = parseexp(nthPL(pl, 2));
return mkVal(var->u.var, exp);
}
if (first == strtoname("use")) {
/*
* <parse [[use]] and return the result>=
*/
if (lengthPL(pl) != 2 || nthPL(pl, 1)->alt != ATOM)
error("%p: usage: (use filename)", p);
return mkUse(nthPL(pl, 1)->u.atom);
}
return mkExp(parseexp(p));
}
}
assert(0);
return NULL;
}
/* parse.c 694a */
static XDef parse(Par p) {
switch (p->alt) {
case ATOM:
/* parse [[atom]] and return the result 694b */
return mkDef(mkExp(parseexp(p)));
case LIST:
/* parse [[list]] and return the result 694c */
{
Name first;
Parlist pl = p->u.list;
if (pl == NULL)
error("%p: empty list", p);
if (nthPL(pl, 0)->alt != ATOM)
error("%p: first item of list not name", p);
first = nthPL(pl, 0)->u.atom;
if (first == strtoname("define")) {
/* parse [[define]] and return the result */
if (lengthPL(pl) != 5 || nthPL(pl, 1)->alt != ATOM ||
nthPL(pl, 2)->alt != LIST || nthPL(pl, 3)->alt != LIST)
error("%p: usage: (define fun (formals) (locals) body)", p);
{
Name name = nthPL(pl, 1)->u.atom;
Namelist formals = getnamelist(name, p, nthPL(pl, 2)->u.list);
Namelist locals = getnamelist(name, p, nthPL(pl, 3)->u.list);
Exp body = parseexp(nthPL(pl, 4));
return mkDef(mkDefine(name, mkUserfun(formals, locals, body)));
}
}
if (first == strtoname("val")) {
/* parse [[val]] and return the result 695c */
Exp var, exp;
if (lengthPL(pl) != 3)
error("%p: usage: (val var exp)", p);
var = parseexp(nthPL(pl, 1));
if (var->alt != VAR)
error("%p: usage: (val var exp) (bad variable)", p);
exp = parseexp(nthPL(pl, 2));
return mkDef(mkVal(var->u.var, exp));
}
if (first == strtoname("use")) {
/* parse [[use]] and return the result 695d */
if (lengthPL(pl) != 2 || nthPL(pl, 1)->alt != ATOM)
error("%p: usage: (use filename)", p);
return mkUse(nthPL(pl, 1)->u.atom);
}
if (first == strtoname("check-expect")) {
/* parse [[check-expect]] and return the result 695e */
Exp check, expect;
if (lengthPL(pl) != 3)
error("%p: usage: (check-expect exp exp)", p);
check = parseexp(nthPL(pl, 1));
expect = parseexp(nthPL(pl, 2));
return mkTest(mkCheckExpect(check, expect));
}
if (first == strtoname("check-error")) {
/* parse [[check-error]] and return the result 696a */
Exp check;
if (lengthPL(pl) != 2)
error("%p: usage: (check-error exp)", p);
check = parseexp(nthPL(pl, 1));
return mkTest(mkCheckError(check));
}
return mkDef(mkExp(parseexp(p)));
}
}
assert(0);
return NULL;
}