Re: How do I create a programming language?
From: Ed Davis (ed_davis2_at_yahoo.com)
Date: 12/16/03
- Next message: Edward G. Nilges: "Re: Nilgewater (was: Letter to US Sen. Byron Dorgan re unpaid overtime)"
- Previous message: Wolfgang Riedel: "Re: Programmer's unpaid overtime."
- In reply to: Leif K-Brooks: "Re: How do I create a programming language?"
- Next in thread: Arthur J. O'Dwyer: "Re: How do I create a programming language?"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Date: 16 Dec 2003 08:04:22 -0800
Leif K-Brooks <eurleif@ecritters.biz> wrote:
> I'm not really at the stage of language design yet, I'm just trying to
> figure out how to write basic parsers. I would be happy with a print
> statment and simple arithmetic (print 2+2 resulting in 4 being
> displayed, for instance).
Here is a little language interpreter that supports printing of
simple integer arithmetic expressions. An example run might be:
tiny <test
Where test contains:
print "Hello", " ", "World!"
print " "
print 1000000 + 2000000 + 3000000
print " "
print "Good bye"
This would display:
Hello World! 6000000 Good bye
Code follows:
/****************************************************************
program = {printstmt}.
printstmt = PRINT expr|string {, expr|string}.
expr = term {addop term}.
term = factor {mulop factor}.
factor = integer | "(" expr ")".
****************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <ctype.h>
typedef enum {EOI,STRING='"',LPAREN='(',RPAREN=')',MULTIPLY='*',
PLUS='+',COMMA=',',MINUS='-',DIVIDE='/',INTEGER,PRINT,IDENT}
Symbol;
typedef enum {OP_HALT, OP_PUSH_INT, OP_ADD, OP_SUB, OP_MUL,
OP_DIV, OP_PRT_STR, OP_PRT_INT} Opcode;
typedef unsigned char uchar;
#define MAX_ID_LEN 255
#define MAXCODE 200
#define MAXSTACK 100
typedef struct {
Symbol sym;
int num;
int str_len;
char str[MAX_ID_LEN];
} Token;
Token tok;
uchar code[MAXCODE];
int codeindex;
void expr(void);
void error(const char *fmt, ...) {
char buf[255];
va_list argptr;
va_start(argptr, fmt);
vsprintf(buf, fmt, argptr);
va_end(argptr);
printf(buf);
exit(1);
}
/*** Byte-code interpreter **************************************/
int get_int_from_code(int *pc) {
int data;
memcpy(&data, &code[*pc], sizeof(data));
(*pc) += sizeof(data);
return data;
}
void interpret(const int maxcode) {
int pc; // program counter
int sp; // stack pointer
int halted; // status
int stack[MAXSTACK]; // runtime stack
halted = pc = sp = 0;
do {
Opcode opcode;
int operand;
opcode = code[pc++];
if (pc > maxcode) error("pc > maxcode");
if (sp >= MAXSTACK) error("stack overflow");
if (sp < 0) error("stack underflow");
switch (opcode) {
case OP_PUSH_INT:
stack[sp++] = get_int_from_code(&pc);
break;
case OP_ADD: sp--; stack[sp - 1] += stack[sp]; break;
case OP_SUB: sp--; stack[sp - 1] -= stack[sp]; break;
case OP_MUL: sp--; stack[sp - 1] *= stack[sp]; break;
case OP_DIV:
sp--;
if (stack[sp] == 0) error("divide by zero");
stack[sp - 1] /= stack[sp];
break;
case OP_PRT_STR:
for (operand = get_int_from_code(&pc);
operand;
operand--) {
printf("%c", code[pc++]);
}
break;
case OP_PRT_INT: sp--; printf("%d", stack[sp]); break;
case OP_HALT: halted++; break;
default: error("Unknown opcode %d\n", opcode);
}
} while (!halted);
}
/*** Code emitting **********************************************/
void emit(int opcode) {
if (codeindex >= MAXCODE)
error("too much code - need to increase codesize\n");
code[codeindex++] = (uchar)opcode;
}
void emit2(int opcode, int operand) {
emit(opcode);
memcpy(&code[codeindex], &operand, sizeof(operand));
codeindex += sizeof(operand);
}
/*** Scanner or Lexical analyzer ********************************/
void getdigit(int ch) {
tok.num = 0; tok.sym = INTEGER;
do {
tok.num = 10 * tok.num + (ch - '0');
} while ((ch = getc(stdin)) >= 0 && isdigit(ch));
ungetc(ch, stdin);
}
void getident(int ch) {
int k = 0; tok.sym = IDENT;
do {
if (k < MAX_ID_LEN) {
tok.str[k] = (char)ch;
k++;
}
} while ((ch = getc(stdin)) >= 0 && isalnum(ch));
tok.str[k] = '\0';
ungetc(ch, stdin);
if (stricmp(tok.str, "PRINT") == 0) tok.sym = PRINT;
}
void getstring(int ch) {
int k = 0; tok.sym = STRING;
while ((ch = getc(stdin)) >= 0 && ch != '"') {
if (k < MAX_ID_LEN) {
tok.str[k] = (char)ch;
k++;
}
}
tok.str[k] = '\0'; tok.str_len = k;
}
void gettok(void) {
for (;;) {
int ch = getc(stdin);
switch (ch) {
case '\n': case '\t': case '\r': case ' ': continue;
case '+': case '-': case '*': case '/': case ',': case '(':
case ')': tok.sym = (Symbol)ch; return;
case '"': getstring(ch); return;
case -1: tok.sym = EOI; return;
default:
if (isdigit(ch)) { getdigit(ch); return; }
if (isalpha(ch)) { getident(ch); return; }
error("unrecognized character %c\n", ch);
}
}
}
/*** Parser *****************************************************/
void factor(void) {
switch (tok.sym) {
case INTEGER: emit2(OP_PUSH_INT, tok.num); gettok(); break;
case LPAREN:
gettok();
expr();
if (tok.sym != RPAREN) error("expecting ')'");
gettok();
break;
default: error("expecting number"); break;
}
}
void term(void) {
factor();
for (;;) {
Opcode opcode;
switch (tok.sym) {
case MULTIPLY: opcode = OP_MUL; break;
case DIVIDE: opcode = OP_DIV; break;
default: return;
}
gettok(); factor(); emit(opcode);
}
}
void expr(void) {
term();
for (;;) {
Opcode opcode;
switch (tok.sym) {
case PLUS: opcode = OP_ADD; break;
case MINUS: opcode = OP_SUB; break;
default: return;
}
gettok(); term(); emit(opcode);
}
}
void do_string(void) {
int i;
for (i = 0; i < tok.str_len; i++) emit(tok.str[i]);
gettok();
}
void printstmt(void) {
do {
gettok();
if (tok.sym == STRING) {
emit2(OP_PRT_STR, tok.str_len); do_string();
} else if (tok.sym == INTEGER) {
expr(); emit(OP_PRT_INT);
} else error("expecting string or integer");
} while (tok.sym == COMMA);
}
void parse(void) {
gettok();
while (tok.sym == PRINT) printstmt();
if (tok.sym != EOI) error("PRINT expected");
emit(OP_HALT);
}
int main(void) {
parse();
interpret(codeindex);
return 0;
}
- Next message: Edward G. Nilges: "Re: Nilgewater (was: Letter to US Sen. Byron Dorgan re unpaid overtime)"
- Previous message: Wolfgang Riedel: "Re: Programmer's unpaid overtime."
- In reply to: Leif K-Brooks: "Re: How do I create a programming language?"
- Next in thread: Arthur J. O'Dwyer: "Re: How do I create a programming language?"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Relevant Pages
|
