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syntax.c
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#include "lisp.h"
#define I(x) St_Intern(x)
static void validate_bindings(StObject args)
{
if (ST_NULLP(args))
{
return;
}
if (!St_ListP(args))
{
St_Error("let: malformed bindings");
}
ST_FOREACH(p, args) {
StObject b = ST_CAR(p);
if (!ST_PAIRP(b) || St_Length(b) != 2 || !ST_SYMBOLP(ST_CAR(b)))
{
St_Error("let: malformed binding");
}
}
}
static StObject syntax_let(StObject module, StObject expr)
{
// (let <bindings> <body>)
// <bindings> ::= ((sym <expr>)*)
// =>
// ((lambda (s1 s2 s3 ...) body) e1 e2 e3 ...)
if (St_Length(expr) < 2)
{
St_Error("let: malformed let");
}
StObject bindings = ST_CADR(expr);
StObject body = ST_CDDR(expr);
validate_bindings(bindings);
bindings = St_Reverse(bindings);
StObject syms = Nil, symst = Nil;
StObject vals = Nil, valst = Nil;
ST_FOREACH(p, bindings) {
ST_APPEND1(syms, symst, ST_CAAR(p));
ST_APPEND1(vals, valst, ST_CADR(ST_CAR(p)));
}
StObject lambda = St_Cons(I("lambda"), St_Cons(syms, body));
StObject ret = St_Cons(lambda, vals);
return St_SyntaxExpand(module, ret);
}
static StObject syntax_let1(StObject module, StObject expr)
{
if (St_Length(expr) < 3)
{
St_Error("let1: malformed let1");
}
if (!ST_SYMBOLP(ST_CADR(expr)))
{
St_Error("let1: malformed let1, symbol requrired");
}
StObject sym = ST_CADR(expr);
StObject val = ST_CADDR(expr);
StObject body = ST_CDR(ST_CDDR(expr));
StObject ret = St_Cons(I("let"), St_Cons(ST_LIST1(ST_LIST2(sym, val)), body));
return St_SyntaxExpand(module, ret);
}
static StObject syntax_letrec(StObject module, StObject expr)
{
// (letrec <bindings> <body>)
// <bindings> ::= ((sym <expr>)*)
// =>
// ((lambda () (define s1 e1) (define e2 s2) ... body))
if (St_Length(expr) < 2)
{
St_Error("letrec: malformed letrec");
}
StObject bindings = ST_CADR(expr);
StObject body = ST_CDDR(expr);
validate_bindings(bindings);
StObject ds = Nil, t = Nil;
ST_FOREACH(p, bindings) {
StObject s = ST_CAAR(p);
StObject e = ST_CAR(ST_CDAR(p));
ST_APPEND1(ds, t, ST_LIST3(I("define"), s, St_SyntaxExpand(module, e)));
}
return ST_LIST1(St_Cons(I("lambda"),
St_Cons(Nil,
St_Cons(St_Cons(I("begin"), ds),
St_SyntaxExpand(module, body)))));
}
static StObject syntax_define(StObject module, StObject expr)
{
if (St_Length(expr) < 2)
{
St_Error("define: malformed define");
}
if (ST_PAIRP(ST_CADR(expr)))
{
StObject sym = ST_CAR(ST_CADR(expr));
StObject vars = ST_CDR(ST_CADR(expr));
StObject body = ST_CDDR(expr);
StObject lambda = St_Cons(I("lambda"), St_Cons(vars, body));
StObject ret = St_Cons(I("define"),
St_Cons(St_SyntaxExpand(module, sym),
ST_LIST1(St_SyntaxExpand(module, lambda))));
return ret;
}
return St_Cons(ST_CAR(expr), St_SyntaxExpand(module, ST_CDR(expr)));
}
static StObject cond_expand(StObject expr)
{
if (ST_NULLP(expr))
{
return Nil;
}
if (ST_PAIRP(expr) && ST_PAIRP(ST_CAR(expr)))
{
StObject pred = ST_CAAR(expr);
StObject body = ST_CDAR(expr);
if (pred != I("else"))
{
return ST_LIST4(I("if"), pred,
St_Cons(I("begin"), body),
cond_expand(ST_CDR(expr)));
}
else
{
return St_Cons(I("begin"), body);
}
}
St_Error("cond: malformed cond clause");
}
static StObject syntax_cond(StObject module, StObject expr)
{
return St_SyntaxExpand(module, cond_expand(ST_CDR(expr)));
}
static StObject case_expand(StObject sym, StObject expr)
{
if (ST_NULLP(expr))
{
return Nil;
}
if (ST_PAIRP(expr) && ST_PAIRP(ST_CAR(expr)))
{
StObject vals = ST_CAAR(expr);
StObject body = ST_CDAR(expr);
if (vals != I("else"))
{
return ST_LIST4(I("if"), ST_LIST3(I("memv"), sym, ST_LIST2(I("quote"), vals)),
St_Cons(I("begin"), body),
case_expand(sym, ST_CDR(expr)));
}
else
{
return St_Cons(I("begin"), body);
}
}
St_Error("case: malformed case clause");
}
static StObject syntax_case(StObject module, StObject expr)
{
int len = St_Length(expr);
if (len < 3)
{
St_Error("case: malformed case");
}
StObject sym = St_Gensym();
StObject val = ST_CADR(expr);
StObject body = ST_CDDR(expr);
StObject ret = ST_LIST4(I("let1"), sym, val, case_expand(sym, body));
return St_SyntaxExpand(module, ret);
}
void St_InitSyntax(void)
{
StObject m = GlobalModule;
St_AddSyntax(m, "let", syntax_let);
St_AddSyntax(m, "let*", syntax_let);
St_AddSyntax(m, "let1", syntax_let1);
St_AddSyntax(m, "letrec", syntax_letrec);
St_AddSyntax(m, "letrec*", syntax_letrec);
St_AddSyntax(m, "define", syntax_define);
St_AddSyntax(m, "cond", syntax_cond);
St_AddSyntax(m, "case", syntax_case);
}