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ActiveTcl User Guide |  |
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ActiveTcl User Guide | |
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 information is left at *parsePtr.
Tcl_ParseExpr parses Tcl expressions. Given a pointer to a script containing an expression, Tcl_ParseExpr 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 information 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 successfully, 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 occurs while parsing the string then TCL_ERROR is returned, an error message 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 location given by *termPtr. If an error occurs while parsing the string then TCL_ERROR is returned, an error message is left in interp's result, and no information is left at *parsePtr 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 parsePtr with information about the structure of the variable name (see below for details). If an error occurs 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 argument. 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_EvalTokensStandard 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_EvalTokensStandard performs the substitutions requested by the tokens and concatenates the resulting values. The return value from Tcl_EvalTokensStandard is a Tcl completion code with one of the values TCL_OK, TCL_ERROR, TCL_RETURN, TCL_BREAK, or TCL_CONTINUE, or possibly some other integer value originating in an extension. In addition, a result value or error message is left in interp's result; it can be retrieved using Tcl_GetObjResult.
Tcl_EvalTokens differs from Tcl_EvalTokensStandard only in the return convention used: it 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 or other exception occurs while evaluating the tokens (such as a reference to a non-existent variable) then the return value is NULL and an error message is left in interp's result. The use of Tcl_EvalTokens is deprecated.
typedef struct Tcl_Parse {
CONST char *commentStart;
int commentSize;
CONST char *commandStart;
int commandSize;
int numWords;
Tcl_Token *tokenPtr;
int numTokens;
...
} Tcl_Parse;
typedef struct Tcl_Token {
int type;
CONST 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 information that describes one Tcl command and any comments that precede the command. If there are comments, the commentStart 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 terminates 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:
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 followed 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 expression. 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 commentStart, 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 consist 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 modified: the commentStart, commentSize, commandStart, and commandSize 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, commandStart, 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.
Copyright © 1997 Sun Microsystems, Inc. Copyright © 1995-1997 Roger E. Critchlow Jr.