units.y

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

%{
#include <u.h>
#include <libc.h>
#include <bio.h>

enum
{
	Ndim	= 15,		/* number of dimensions */
	Nsym	= 40,		/* size of a name */
	Nvar	= 203,		/* hash table size */
	Maxe	= 695,		/* log of largest number */
};

typedef	struct	Var	Var;
typedef	struct	Node	Node;
typedef	struct	Prefix	Prefix;

struct	Node
{
	double	val;
	schar	dim[Ndim];
};
struct	Var
{
	Rune	name[Nsym];
	Node	node;
	Var*	link;
};
struct	Prefix
{
	double	val;
	Rune*	pname;
};

char	buf[100];
int	digval;
Biobuf*	fi;
Biobuf	linebuf;
Var*	fund[Ndim];
Rune	line[1000];
ulong	lineno;
int	linep;
int	nerrors;
Node	one;
int	peekrune;
Node	retnode1;
Node	retnode2;
Node	retnode;
Rune	sym[Nsym];
Var*	vars[Nvar];
int	vflag;

extern	void	add(Node*, Node*, Node*);
extern	void	div(Node*, Node*, Node*);
extern	int	specialcase(Node*, Node*, Node*);
extern	double	fadd(double, double);
extern	double	fdiv(double, double);
extern	double	fmul(double, double);
extern	int	gdigit(void*);
extern	Var*	lookup(int);
extern	void	main(int, char*[]);
extern	void	mul(Node*, Node*, Node*);
extern	void	ofile(void);
extern	double	pname(void);
extern	void	printdim(char*, int, int);
extern	int	ralpha(int);
extern	int	readline(void);
extern	void	sub(Node*, Node*, Node*);
extern	int	Ufmt(Fmt*);
extern	void	xpn(Node*, Node*, int);
extern	void	yyerror(char*, ...);
extern	int	yylex(void);
extern	int	yyparse(void);

typedef	Node*	indnode;
#pragma	varargck	type	"U"	indnode

%}
%union
{
	Node	node;
	Var*	var;
	int	numb;
	double	val;
}

%type	<node>	prog expr expr0 expr1 expr2 expr3 expr4

%token	<val>	VAL
%token	<var>	VAR
%token	<numb>	SUP
%%
prog:
	':' VAR expr
	{
		int f;

		f = $2->node.dim[0];
		$2->node = $3;
		$2->node.dim[0] = 1;
		if(f)
			yyerror("redefinition of %S", $2->name);
		else
		if(vflag)
			print("%S\t%U\n", $2->name, &$2->node);
	}
|	':' VAR '#'
	{
		int f, i;

		for(i=1; i<Ndim; i++)
			if(fund[i] == 0)
				break;
		if(i >= Ndim) {
			yyerror("too many dimensions");
			i = Ndim-1;
		}
		fund[i] = $2;

		f = $2->node.dim[0];
		$2->node = one;
		$2->node.dim[0] = 1;
		$2->node.dim[i] = 1;
		if(f)
			yyerror("redefinition of %S", $2->name);
		else
		if(vflag)
			print("%S\t#\n", $2->name);
	}
|	'?' expr
	{
		retnode1 = $2;
	}
|	'?'
	{
		retnode1 = one;
	}

expr:
	expr4
|	expr '+' expr4
	{
		add(&$$, &$1, &$3);
	}
|	expr '-' expr4
	{
		sub(&$$, &$1, &$3);
	}

expr4:
	expr3
|	expr4 '*' expr3
	{
		mul(&$$, &$1, &$3);
	}
|	expr4 '/' expr3
	{
		div(&$$, &$1, &$3);
	}

expr3:
	expr2
|	expr3 expr2
	{
		mul(&$$, &$1, &$2);
	}

expr2:
	expr1
|	expr2 SUP
	{
		xpn(&$$, &$1, $2);
	}
|	expr2 '^' expr1
	{
		int i;

		for(i=1; i<Ndim; i++)
			if($3.dim[i]) {
				yyerror("exponent has units");
				$$ = $1;
				break;
			}
		if(i >= Ndim) {
			i = $3.val;
			if(i != $3.val)
				yyerror("exponent not integral");
			xpn(&$$, &$1, i);
		}
	}

expr1:
	expr0
|	expr1 '|' expr0
	{
		div(&$$, &$1, &$3);
	}

expr0:
	VAR
	{
		if($1->node.dim[0] == 0) {
			yyerror("undefined %S", $1->name);
			$$ = one;
		} else
			$$ = $1->node;
	}
|	VAL
	{
		$$ = one;
		$$.val = $1;
	}
|	'(' expr ')'
	{
		$$ = $2;
	}
%%

int
yylex(void)
{
	int c, i;

	c = peekrune;
	peekrune = ' ';

loop:
	if((c >= '0' && c <= '9') || c == '.')
		goto numb;
	if(ralpha(c))
		goto alpha;
	switch(c) {
	case ' ':
	case '\t':
		c = line[linep++];
		goto loop;
	case L'脳':
		return '*';
	case L'梅':
		return '/';
	case L'鹿':
	case L'鈦