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NAME
Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces,
Tcl_ParseQuotedString, Tcl_ParseVarName, Tcl_ParseVar,
Tcl_FreeParse, Tcl_EvalTokens - parse Tcl scripts and
expressions
SYNOPSIS
#include <tcl.h>
int
Tcl_ParseCommand(interp, string, numBytes, nested, parsePtr)
int
Tcl_ParseExpr(interp, string, numBytes, parsePtr)
int
Tcl_ParseBraces(interp, string, numBytes, parsePtr, append, termPtr)
int
Tcl_ParseQuotedString(interp, string, numBytes, parsePtr, append, termPtr)
int
Tcl_ParseVarName(interp, string, numBytes, parsePtr, append)
char *
Tcl_ParseVar(interp, string, termPtr)
Tcl_FreeParse(usedParsePtr)
Tcl_Obj *
Tcl_EvalTokens(interp, tokenPtr, numTokens)
ARGUMENTS
Tcl_Interp *interp (out) For procedures other
than Tcl_FreeParse
and Tcl_EvalTokens,
used only for error
reporting; if NULL,
then no error mes-
sages are left after
errors. For
Tcl_EvalTokens,
determines the con-
text for evaluating
the script and also
is used for error
reporting; must not
be NULL.
char *string (in) Pointer to first
character in string
to parse.
int numBytes (in) Number of bytes in
string, not including
any terminating null
character. If less
than 0 then the
script consists of
all characters in
string up to the
first null character.
int nested (in) Non-zero means that
the script is part of
a command substitu-
tion so an unquoted
close bracket should
be treated as a com-
mand terminator. If
zero, close brackets
have no special mean-
ing.
int append (in) Non-zero means that
*parsePtr already
contains valid
tokens; the new
tokens should be
appended to those
already present.
Zero means that *par-
sePtr is uninitial-
ized; any information
in it is ignored.
This argument is nor-
mally 0.
Tcl_Parse *parsePtr (out) Points to structure
to fill in with
information about the
parsed command,
expression, variable
name, etc. Any pre-
vious information in
this structure is
ignored, unless
append is non-zero in
a call to
Tcl_ParseBraces,
Tcl_ParseQuotedString,
or Tcl_ParseVarName.
char **termPtr (out) If not NULL, points
to a location where
Tcl_ParseBraces,
Tcl_ParseQuotedString,
and Tcl_ParseVar will
store a pointer to
the character just
after the terminating
character (the
close-brace, the last
character of the
variable name, or the
close-quote (respec-
tively)) if the parse
was successful.
Tcl_Parse *usedParsePtr (in) Points to structure
that was filled in by
a previous call to
Tcl_ParseCommand,
Tcl_ParseExpr,
Tcl_ParseVarName,
etc.
_________________________________________________________________
DESCRIPTION
These procedures parse Tcl commands or portions of Tcl com-
mands such as expressions or references to variables. Each
procedure takes a pointer to a script (or portion thereof)
and fills in the structure pointed to by parsePtr with a
collection of tokens describing the information that was
parsed. The procedures normally return TCL_OK. However, if
an error occurs then they return TCL_ERROR, leave an error
message in interp's result (if interp is not NULL), and
leave nothing in parsePtr.
Tcl_ParseCommand is a procedure that parses Tcl scripts.
Given a pointer to a script, it parses the first command
from the script. If the command was parsed successfully,
Tcl_ParseCommand returns TCL_OK and fills in the structure
pointed to by parsePtr with information about the structure
of the command (see below for details). If an error
occurred in parsing the command then TCL_ERROR is returned,
an error message is left in interp's result, and no informa-
tion is left at *parsePtr.
Tcl_ParseExpr parses Tcl expressions. Given a pointer to a
script containing an expression, Tcl_ParseCommand parses the
expression. If the expression was parsed successfully,
Tcl_ParseExpr returns TCL_OK and fills in the structure
pointed to by parsePtr with information about the structure
of the expression (see below for details). If an error
occurred in parsing the command then TCL_ERROR is returned,
an error message is left in interp's result, and no informa-
tion is left at *parsePtr.
Tcl_ParseBraces parses a string or command argument enclosed
in braces such as {hello} or {string \t with \t tabs} from
the beginning of its argument string. The first character
of string must be {. If the braced string was parsed suc-
cessfully, Tcl_ParseBraces returns TCL_OK, fills in the
structure pointed to by parsePtr with information about the
structure of the string (see below for details), and stores
a pointer to the character just after the terminating } in
the location given by *termPtr. If an error occurrs while
parsing the string then TCL_ERROR is returned, an error mes-
sage is left in interp's result, and no information is left
at *parsePtr or *termPtr.
Tcl_ParseQuotedString parses a double-quoted string such as
"sum is [expr $a+$b]" from the beginning of the argument
string. The first character of string must be ". If the
double-quoted string was parsed successfully,
Tcl_ParseQuotedString returns TCL_OK, fills in the structure
pointed to by parsePtr with information about the structure
of the string (see below for details), and stores a pointer
to the character just after the terminating " in the loca-
tion given by *termPtr. If an error occurrs while parsing
the string then TCL_ERROR is returned, an error message is
left in interp's result, and no information is left at *par-
sePtr or *termPtr.
Tcl_ParseVarName parses a Tcl variable reference such as
$abc or $x([expr $index + 1]) from the beginning of its
string argument. The first character of string must be $.
If a variable name was parsed successfully, Tcl_ParseVarName
returns TCL_OK and fills in the structure pointed to by par-
sePtr with information about the structure of the variable
name (see below for details). If an error occurrs while
parsing the command then TCL_ERROR is returned, an error
message is left in interp's result (if interp isn't NULL),
and no information is left at *parsePtr.
Tcl_ParseVar parse a Tcl variable reference such as $abc or
$x([expr $index + 1]) from the beginning of its string argu-
ment. The first character of string must be $. If the
variable name is parsed successfully, Tcl_ParseVar returns a
pointer to the string value of the variable. If an error
occurs while parsing, then NULL is returned and an error
message is left in interp's result.
The information left at *parsePtr by Tcl_ParseCommand,
Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, and
Tcl_ParseVarName may include dynamically allocated memory.
If these five parsing procedures return TCL_OK then the
caller must invoke Tcl_FreeParse to release the storage at
*parsePtr. These procedures ignore any existing information
in *parsePtr (unless append is non-zero), so if repeated
calls are being made to any of them then Tcl_FreeParse must
be invoked once after each call.
Tcl_EvalTokens evaluates a sequence of parse tokens from a
Tcl_Parse structure. The tokens typically consist of all
the tokens in a word or all the tokens that make up the
index for a reference to an array variable. Tcl_EvalTokens
performs the substitutions requested by the tokens, con-
catenates the resulting values, and returns the result in a
new Tcl_Obj. The reference count of the object returned as
result has been incremented, so the caller must invoke
Tcl_DecrRefCount when it is finished with the object. If an
error occurs while evaluating the tokens (such as a refer-
ence to a non-existent variable) then the return value is
NULL and an error message is left in interp's result.
TCL_PARSE STRUCTURE
Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces,
Tcl_ParseQuotedString, and Tcl_ParseVarName return parse
information in two data structures, Tcl_Parse and Tcl_Token:
typedef struct Tcl_Parse {
char *commentStart;
int commentSize;
char *commandStart;
int commandSize;
int numWords;
Tcl_Token *tokenPtr;
int numTokens;
...
} Tcl_Parse;
typedef struct Tcl_Token {
int type;
char *start;
int size;
int numComponents;
} Tcl_Token;
The first five fields of a Tcl_Parse structure are filled in
only by Tcl_ParseCommand. These fields are not used by the
other parsing procedures.
Tcl_ParseCommand fills in a Tcl_Parse structure with infor-
mation that describes one Tcl command and any comments that
precede the command. If there are comments, the com-
mentStart field points to the # character that begins the
first comment and commentSize indicates the number of bytes
in all of the comments preceding the command, including the
newline character that terminates the last comment. If the
command is not preceded by any comments, commentSize is 0.
Tcl_ParseCommand also sets the commandStart field to point
to the first character of the first word in the command
(skipping any comments and leading space) and commandSize
gives the total number of bytes in the command, including
the character pointed to by commandStart up to and including
the newline, close bracket, or semicolon character that ter-
minates the command. The numWords field gives the total
number of words in the command.
All parsing procedures set the remaining fields, tokenPtr
and numTokens. The tokenPtr field points to the first in an
array of Tcl_Token structures that describe the components
of the entity being parsed. The numTokens field gives the
total number of tokens present in the array. Each token
contains four fields. The type field selects one of several
token types that are described below. The start field
points to the first character in the token and the size
field gives the total number of characters in the token.
Some token types, such as TCL_TOKEN_WORD and
TCL_TOKEN_VARIABLE, consist of several component tokens,
which immediately follow the parent token; the numComponents
field describes how many of these there are. The type field
has one of the following values:
TCL_TOKEN_WORD This token ordinarily describes one word
of a command but it may also describe a
quoted or braced string in an expres-
sion. The token describes a component
of the script that is the result of con-
catenating together a sequence of sub-
components, each described by a separate
subtoken. The token starts with the
first non-blank character of the com-
ponent (which may be a double-quote or
open brace) and includes all characters
in the component up to but not including
the space, semicolon, close bracket,
close quote, or close brace that ter-
minates the component. The numCom-
ponents field counts the total number of
sub-tokens that make up the word,
including sub-tokens of
TCL_TOKEN_VARIABLE and TCL_TOKEN_BS
tokens.
TCL_TOKEN_SIMPLE_WORD
This token has the same meaning as
TCL_TOKEN_WORD, except that the word is
guaranteed to consist of a single
TCL_TOKEN_TEXT sub-token. The numCom-
ponents field is always 1.
TCL_TOKEN_TEXT The token describes a range of literal
text that is part of a word. The
numComponents field is always 0.
TCL_TOKEN_BS The token describes a backslash sequence
such as \n or \0xa3. The numComponents
field is always 0.
TCL_TOKEN_COMMAND The token describes a command whose
result result must be substituted into
the word. The token includes the square
brackets that surround the command. The
numComponents field is always 0 (the
nested command is not parsed; call
Tcl_ParseCommand recursively if you want
to see its tokens).
TCL_TOKEN_VARIABLE The token describes a variable substitu-
tion, including the $, variable name,
and array index (if there is one) up
through the close parenthesis that ter-
minates the index. This token is fol-
lowed by one or more additional tokens
that describe the variable name and
array index. If numComponents is 1
then the variable is a scalar and the
next token is a TCL_TOKEN_TEXT token
that gives the variable name. If
numComponents is greater than 1 then the
variable is an array: the first sub-
token is a TCL_TOKEN_TEXT token giving
the array name and the remaining sub-
tokens are TCL_TOKEN_TEXT, TCL_TOKEN_BS,
TCL_TOKEN_COMMAND, and
TCL_TOKEN_VARIABLE tokens that must be
concatenated to produce the array index.
The numComponents field includes nested
sub-tokens that are part of
TCL_TOKEN_VARIABLE tokens in the array
index.
TCL_TOKEN_SUB_EXPR The token describes one subexpression of
an expression (or an entire expression).
A subexpression may consist of a value
such as an integer literal, variable
substitution, or parenthesized subex-
pression; it may also consist of an
operator and its operands. The token
starts with the first non-blank charac-
ter of the subexpression up to but not
including the space, brace, close-paren,
or bracket that terminates the subex-
pression. This token is followed by one
or more additional tokens that describe
the subexpression. If the first sub-
token after the TCL_TOKEN_SUB_EXPR token
is a TCL_TOKEN_OPERATOR token, the
subexpression consists of an operator
and its token operands. If the operator
has no operands, the subexpression con-
sists of just the TCL_TOKEN_OPERATOR
token. Each operand is described by a
TCL_TOKEN_SUB_EXPR token. Otherwise,
the subexpression is a value described
by one of the token types
TCL_TOKEN_WORD, TCL_TOKEN_TEXT,
TCL_TOKEN_BS, TCL_TOKEN_COMMAND,
TCL_TOKEN_VARIABLE, and
TCL_TOKEN_SUB_EXPR. The numComponents
field counts the total number of sub-
tokens that make up the subexpression;
this includes the sub-tokens for any
nested TCL_TOKEN_SUB_EXPR tokens.
TCL_TOKEN_OPERATOR The token describes one operator of an
expression such as && or hypot. An
TCL_TOKEN_OPERATOR token is always pre-
ceeded by a TCL_TOKEN_SUB_EXPR token
that describes the operator and its
operands; the TCL_TOKEN_SUB_EXPR token's
numComponents field can be used to
determine the number of operands. A
binary operator such as * is followed by
two TCL_TOKEN_SUB_EXPR tokens that
describe its operands. A unary operator
like - is followed by a single
TCL_TOKEN_SUB_EXPR token for its
operand. If the operator is a math
function such as log10, the
TCL_TOKEN_OPERATOR token will give its
name and the following
TCL_TOKEN_SUB_EXPR tokens will describe
its operands; if there are no operands
(as with rand), no TCL_TOKEN_SUB_EXPR
tokens follow. There is one trinary
operator, ?, that appears in if-then-
else subexpressions such as x?y:z; in
this case, the ? TCL_TOKEN_OPERATOR
token is followed by three
TCL_TOKEN_SUB_EXPR tokens for the
operands x, y, and z. The numComponents
field for a TCL_TOKEN_OPERATOR token is
always 0.
After Tcl_ParseCommand returns, the first token pointed to
by the tokenPtr field of the Tcl_Parse structure always has
type TCL_TOKEN_WORD or TCL_TOKEN_SIMPLE_WORD. It is fol-
lowed by the sub-tokens that must be concatenated to produce
the value of that word. The next token is the
TCL_TOKEN_WORD or TCL_TOKEN_SIMPLE_WORD token for the second
word, followed by sub-tokens for that word, and so on until
all numWords have been accounted for.
After Tcl_ParseExpr returns, the first token pointed to by
the tokenPtr field of the Tcl_Parse structure always has
type TCL_TOKEN_SUB_EXPR. It is followed by the sub-tokens
that must be evaluated to produce the value of the expres-
sion. Only the token information in the Tcl_Parse structure
is modified: the commentStart, commentSize, commandStart,
and commandSize fields are not modified by Tcl_ParseExpr.
After Tcl_ParseBraces returns, the array of tokens pointed
to by the tokenPtr field of the Tcl_Parse structure will
contain a single TCL_TOKEN_TEXT token if the braced string
does not contain any backslash-newlines. If the string does
contain backslash-newlines, the array of tokens will contain
one or more TCL_TOKEN_TEXT or TCL_TOKEN_BS sub-tokens that
must be concatenated to produce the value of the string. If
the braced string was just {} (that is, the string was
empty), the single TCL_TOKEN_TEXT token will have a size
field containing zero; this ensures that at least one token
appears to describe the braced string. Only the token
information in the Tcl_Parse structure is modified: the com-
mentStart, commentSize, commandStart, and commandSize fields
are not modified by Tcl_ParseBraces.
After Tcl_ParseQuotedString returns, the array of tokens
pointed to by the tokenPtr field of the Tcl_Parse structure
depends on the contents of the quoted string. It will con-
sist of one or more TCL_TOKEN_TEXT, TCL_TOKEN_BS,
TCL_TOKEN_COMMAND, and TCL_TOKEN_VARIABLE sub-tokens. The
array always contains at least one token; for example, if
the argument string is empty, the array returned consists of
a single TCL_TOKEN_TEXT token with a zero size field. Only
the token information in the Tcl_Parse structure is modi-
fied: the commentStart, commentSize, commandStart, and com-
mandSize fields are not modified.
After Tcl_ParseVarName returns, the first token pointed to
by the tokenPtr field of the Tcl_Parse structure always has
type TCL_TOKEN_VARIABLE. It is followed by the sub-tokens
that make up the variable name as described above. The
total length of the variable name is contained in the size
field of the first token. As in Tcl_ParseExpr, only the
token information in the Tcl_Parse structure is modified by
Tcl_ParseVarName: the commentStart, commentSize, com-
mandStart, and commandSize fields are not modified.
All of the character pointers in the Tcl_Parse and Tcl_Token
structures refer to characters in the string argument passed
to Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces,
Tcl_ParseQuotedString, and Tcl_ParseVarName.
There are additional fields in the Tcl_Parse structure after
the numTokens field, but these are for the private use of
Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces,
Tcl_ParseQuotedString, and Tcl_ParseVarName; they should not
be referenced by code outside of these procedures.
KEYWORDS
backslash substitution, braces, command, expression, parse,
token, variable substitution
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