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-rw-r--r--toys/pending/expr.c97
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);