diff options
Diffstat (limited to 'toys/pending')
| -rw-r--r-- | toys/pending/expr.c | 97 |
1 files changed, 39 insertions, 58 deletions
diff --git a/toys/pending/expr.c b/toys/pending/expr.c index 71d5d192..ca0507ef 100644 --- a/toys/pending/expr.c +++ b/toys/pending/expr.c @@ -7,6 +7,16 @@ * * The web standard is incomplete (precedence grouping missing), see: * http://permalink.gmane.org/gmane.comp.standards.posix.austin.general/10141 + * + * eval_expr() uses the recursive "Precedence Climbing" algorithm: + * + * Clarke, Keith. "The top-down parsing of expressions." University of London. + * Queen Mary College. Department of Computer Science and Statistics, 1986. + * + * http://www.antlr.org/papers/Clarke-expr-parsing-1986.pdf + * + * Nice explanation and Python implementation: + * http://eli.thegreenplace.net/2012/08/02/parsing-expressions-by-precedence-climbing USE_EXPR(NEWTOY(expr, NULL, TOYFLAG_USR|TOYFLAG_BIN)) @@ -47,7 +57,7 @@ config EXPR #include "toys.h" GLOBALS( - char* tok; // current token, not on the stack since recursive calls mutate it + char *tok; // current token, not on the stack since recursive calls mutate it ) // Scalar value. If s != NULL, it's a string, otherwise it's an int. @@ -56,24 +66,12 @@ struct value { long long i; }; -void syntax_error(char *msg, ...) { - if (0) { // detailed message for debugging. TODO: add CFG_ var to enable - va_list va; - va_start(va, msg); - verror_msg(msg, 0, va); - va_end(va); - xexit(); - } else - error_exit("syntax error"); -} - #define LONG_LONG_MAX_LEN 21 // Get the value as a string. -void get_str(struct value *v, char** ret) +void get_str(struct value *v, char **ret) { - if (v->s) - *ret = v->s; + if (v->s) *ret = v->s; else { *ret = xmalloc(LONG_LONG_MAX_LEN); snprintf(*ret, LONG_LONG_MAX_LEN, "%lld", v->i); @@ -85,12 +83,13 @@ int get_int(struct value *v, long long *ret) { if (v->s) { char *endp; + *ret = strtoll(v->s, &endp, 10); - return *endp ? 0 : 1; // If endp points to NUL, all chars were converted - } else { - *ret = v->i; - return 1; - } + + if (*endp) return 0; // If endp points to NUL, all chars were converted + } else *ret = v->i; + + return 1; } // Preserve the invariant that v.s is NULL when the value is an integer. @@ -103,10 +102,8 @@ void assign_int(struct value *v, long long i) // Check if v is 0 or the empty string. static int is_false(struct value *v) { - if (v->s) - return !*v->s || !strcmp(v->s, "0"); // get_int("0") -> 0 - else - return !v->i; + if (v->s) return !*v->s || !strcmp(v->s, "0"); // get_int("0") -> 0 + return !v->i; } // 'ret' is filled with a string capture or int match position. @@ -117,16 +114,14 @@ static void re(char *target, char *pattern, struct value *ret) xregcomp(&pat, pattern, 0); if (!regexec(&pat, target, 2, m, 0) && m[0].rm_so == 0) { // match at pos 0 - regmatch_t* g1 = &m[1]; // group capture 1 + regmatch_t *g1 = &m[1]; // group capture 1 if (pat.re_nsub > 0 && g1->rm_so >= 0) // has capture ret->s = xmprintf("%.*s", g1->rm_eo - g1->rm_so, target + g1->rm_so); - else - assign_int(ret, m[0].rm_eo); + else assign_int(ret, m[0].rm_eo); } else { // no match - if (pat.re_nsub > 0) // has capture - ret->s = ""; - else - assign_int(ret, 0); + // has capture + if (pat.re_nsub > 0) ret->s = ""; + else assign_int(ret, 0); } } @@ -156,7 +151,8 @@ static struct op_def { {NULL, 0, 0, 0}, // sentinel }; -void eval_op(struct op_def *o, struct value *ret, struct value *rhs) { +void eval_op(struct op_def *o, struct value *ret, struct value *rhs) +{ long long a, b, x = 0; // x = a OP b for ints. char *s, *t; // string operands int cmp; @@ -210,36 +206,22 @@ void eval_op(struct op_def *o, struct value *ret, struct value *rhs) { } } -// Point TT.tok at the next token. It's NULL when there are no more tokens. -void advance() { - TT.tok = *toys.optargs++; -} - -// Evalute a compound expression, setting 'ret'. -// -// This function uses the recursive "Precedence Climbing" algorithm: -// -// Clarke, Keith. "The top-down parsing of expressions." University of London. -// Queen Mary College. Department of Computer Science and Statistics, 1986. -// -// http://www.antlr.org/papers/Clarke-expr-parsing-1986.pdf -// -// Nice explanation and Python implementation: -// http://eli.thegreenplace.net/2012/08/02/parsing-expressions-by-precedence-climbing +// Evalute a compound expression using recursive "Precedence Climbing" +// algorithm, setting 'ret'. static void eval_expr(struct value *ret, int min_prec) { - if (!TT.tok) syntax_error("Unexpected end of input"); + if (!TT.tok) error_exit("Unexpected end of input"); // Evaluate LHS atom, setting 'ret'. if (!strcmp(TT.tok, "(")) { // parenthesized expression - advance(); // consume ( + TT.tok = *toys.optargs++; // consume ( eval_expr(ret, 1); // We're inside ( ), so min_prec = 1 - if (!TT.tok) syntax_error("Expected )"); - if (strcmp(TT.tok, ")")) syntax_error("Expected ) but got %s", TT.tok); - advance(); // consume ) + if (!TT.tok) error_exit("Expected )"); // TODO: Also says that for () + if (strcmp(TT.tok, ")")) error_exit("Expected ) but got %s", TT.tok); + TT.tok = *toys.optargs++; // consume ) } else { // simple literal ret->s = TT.tok; // all values start as strings - advance(); + TT.tok = *toys.optargs++; } // Evaluate RHS and apply operator until precedence is too low. @@ -252,7 +234,7 @@ static void eval_expr(struct value *ret, int min_prec) } if (!o->tok) break; // Not an operator (extra input will fail later) if (o->prec < min_prec) break; // Precedence too low, pop a stack frame - advance(); + TT.tok = *toys.optargs++; eval_expr(&rhs, o->prec + 1); // Evaluate RHS, with higher min precedence eval_op(o, ret, &rhs); // Apply operator, setting 'ret' @@ -263,10 +245,9 @@ void expr_main(void) { struct value ret = {0}; toys.exitval = 2; // if exiting early, indicate error - - advance(); // initialize global token + TT.tok = *toys.optargs++; // initialize global token eval_expr(&ret, 1); - if (TT.tok) syntax_error("Unexpected extra input '%s'\n", TT.tok); + if (TT.tok) error_exit("Unexpected extra input '%s'\n", TT.tok); if (ret.s) printf("%s\n", ret.s); else printf("%lld\n", ret.i); |