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(slib.info)Grammar Rule Definition
Grammar Rule Definition ----------------------- Here are procedures for defining rules for the syntax types introduced in Note: Precedence Parsing Overview. For the rule-defining procedures that follow, the variable TK may be a character, string, or symbol, or a list composed of characters, strings, and symbols. Each element of TK is treated as though the procedure were called for each element. For procedures prec:delim, ..., prec:prestfix, if the SOP argument is `#f', then the token which triggered this rule is converted to a symbol and returned. A false SOP argument to the procedures prec:commentfix, prec:matchfix, or prec:inmatchfix has a different meaning. Character TK arguments will match only character tokens; i.e. characters for which no token-group is assigned. Symbols and strings will both match token strings; i.e. tokens resulting from token groups. - Function: prec:delim tk Returns a rule specifying that TK should not be returned from parsing; i.e. TK's function is purely syntactic. The end-of-file is always treated as a delimiter. - Function: prec:nofix tk sop Returns a rule specifying the following actions take place when TK is parsed: * If SOP is a procedure, it is called with no arguments; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP is incorporated. - Function: prec:prefix tk sop bp rule1 ... Returns a rule specifying the following actions take place when TK is parsed: * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect. * `prec:parse1' is called with binding-power BP. * If SOP is a procedure, it is called with the expression returned from `prec:parse1'; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP and the expression returned from `prec:parse1' is incorporated. * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten. - Function: prec:infix tk sop lbp bp rule1 ... Returns a rule declaring the left-binding-precedence of the token TK is LBP and specifying the following actions take place when TK is parsed: * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect. * One expression is parsed with binding-power LBP. If instead a delimiter is encountered, a warning is issued. * If SOP is a procedure, it is applied to the list of LEFT and the parsed expression; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP, the LEFT expression, and the parsed expression is incorporated. * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten. - Function: prec:nary tk sop bp Returns a rule declaring the left-binding-precedence of the token TK is BP and specifying the following actions take place when TK is parsed: * Expressions are parsed with binding-power BP as far as they are interleaved with the token TK. * If SOP is a procedure, it is applied to the list of LEFT and the parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP, the LEFT expression, and the parsed expressions is incorporated. - Function: prec:postfix tk sop lbp Returns a rule declaring the left-binding-precedence of the token TK is LBP and specifying the following actions take place when TK is parsed: * If SOP is a procedure, it is called with the LEFT expression; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP and the LEFT expression is incorporated. - Function: prec:prestfix tk sop bp rule1 ... Returns a rule specifying the following actions take place when TK is parsed: * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect. * Expressions are parsed with binding-power BP until a delimiter is reached. * If SOP is a procedure, it is applied to the list of parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP and the parsed expressions is incorporated. * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten. - Function: prec:commentfix tk stp match rule1 ... Returns rules specifying the following actions take place when TK is parsed: * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect. * Characters are read until and end-of-file or a sequence of characters is read which matches the _string_ MATCH. * If STP is a procedure, it is called with the string of all that was read between the TK and MATCH (exclusive). * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten. Parsing of commentfix syntax differs from the others in several ways. It reads directly from input without tokenizing; It calls STP but does not return its value; nay any value. I added the STP argument so that comment text could be echoed. - Function: prec:matchfix tk sop sep match rule1 ... Returns a rule specifying the following actions take place when TK is parsed: * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect. * A rule declaring the token MATCH a delimiter takes effect. * Expressions are parsed with binding-power `0' until the token MATCH is reached. If the token SEP does not appear between each pair of expressions parsed, a warning is issued. * If SOP is a procedure, it is applied to the list of parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP and the parsed expressions is incorporated. * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten. - Function: prec:inmatchfix tk sop sep match lbp rule1 ... Returns a rule declaring the left-binding-precedence of the token TK is LBP and specifying the following actions take place when TK is parsed: * The rules RULE1 ... augment and, in case of conflict, override rules currently in effect. * A rule declaring the token MATCH a delimiter takes effect. * Expressions are parsed with binding-power `0' until the token MATCH is reached. If the token SEP does not appear between each pair of expressions parsed, a warning is issued. * If SOP is a procedure, it is applied to the list of LEFT and the parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of SOP, the LEFT expression, and the parsed expressions is incorporated. * The ruleset in effect before TK was parsed is restored; RULE1 ... are forgotten.
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