%{
#include "lambda.h"
#include "lambda.tab.h"
#include "mem.h"

struct lambda *result;
extern int yylex();

int yydebug=1;
void yyerror(const char *str)
{
	fprintf(stderr, "parse error: %s\n", str);
}

int yywrap()
{
	return 1;
}

struct lambda *make_lambda()
{
	return malloc(sizeof (struct lambda));
}

struct lambda *make_ident(char *i)
{
	struct lambda *r = make_lambda();
	r->which = lambda_ident;
	r->data.identifier = strdup(i);
	return r;
}

struct lambda *make_abstraction(char *i, struct lambda *t)
{
	struct lambda *r = make_lambda();
	r->which = lambda_abs;
	r->data.abstraction.ident = strdup(i);
	r->data.abstraction.expr = t;
	return r;
}

struct lambda *make_application(struct lambda *t1, struct lambda *t2)
{
	struct lambda *r = make_lambda();
	r->which = lambda_app;
	r->data.application.expr1 = t1;
	r->data.application.expr2 = t2;
	return r;
}

%}

%token LAMBDA DOT OBRACE CBRACE IDENT I K S T F

%%

lambda
	: term
		{ result = $$; }
term
	: term appterm
		{
			$$ = make_application($1, $2);
		}
	| appterm
		{ $$ = $1; }
appterm
	: IDENT
		{
			$$ = make_ident($1->data.identifier);
			lambda_free($1);
		}
	| LAMBDA IDENT DOT term
		{
			$$ = make_abstraction($2->data.identifier, $4);
			lambda_free($2);
		}
	| OBRACE term CBRACE
		{ $$ = $2; }
	| I
		{ $$ = make_abstraction("x", make_ident("x")); }
	| K
		{ $$ = make_abstraction("x", make_abstraction("y", make_ident("x"))); }
	| S
		{ $$ = make_abstraction("x", make_abstraction("y", make_abstraction("z",
			make_application(make_application(make_ident("x"), make_ident("y")),
				make_application(make_ident("y"), make_ident("z"))))));
		}
	| T
		{ $$ = make_abstraction("x", make_abstraction("y", make_ident("x"))); }
	| F
		{ $$ = make_abstraction("x", make_abstraction("y", make_ident("y"))); }