pt::param(n) 1 tcllib "Parser Tools"

Input Handling

The instructions in this section mainly access IN, pulling the characters to process into the machine.

input_next msg

This method reads the next character, i.e. the character after CL, from IN. If successful this character becomes CC, CL is advanced by one, ES is cleared, and the operation is recorded as a success in ST.

The operation may read the character from IN if the next character is not yet known to TC. If successful the new character is stored in TC, with its location (line, column), and the operation otherwise behaves as specified above. Future reads from the same location, possible due to backtracking, will then be satisfied from TC instead of IN.

If, on the other hand, the end of IN was reached, the operation is recorded as failed in ST, CL is left unchanged, and the pair of CL and msg becomes the new ES.

Character Processing

The instructions in this section mainly access CC, testing it against character classes, ranges, and individual characters.

test_alnum

This instruction implements the special PE operator "alnum", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_alpha

This instruction implements the special PE operator "alpha", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_ascii

This instruction implements the special PE operator "ascii", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_char char

This instruction implements the character matching operator, i.e. it checks if CC is char.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_ddigit

This instruction implements the special PE operator "ddigit", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_digit

This instruction implements the special PE operator "digit", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_graph

This instruction implements the special PE operator "graph", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_lower

This instruction implements the special PE operator "lower", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_print

This instruction implements the special PE operator "print", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_punct

This instruction implements the special PE operator "punct", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_range chars chare

This instruction implements the range matching operator, i.e. it checks if CC falls into the interval of characters spanned up by the two characters from chars to chare, both inclusive.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_space

This instruction implements the special PE operator "space", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_upper

This instruction implements the special PE operator "upper", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_wordchar

This instruction implements the special PE operator "wordchar", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

test_xdigit

This instruction implements the special PE operator "xdigit", which checks if CC falls into the character class of the same name, or not.

Success and failure of the test are both recorded directly in ST. Success further clears ES, wheras failure sets the pair of CL and expected input (encoded as a leaf parsing expression) as the new ES and then rewinds CL by one character, preparing the machine for another parse attempt by a possible alternative.

Error Handling

The instructions in this section mainly access ER and ES.

error_clear

This instruction clears ER.

error_push

This instruction makes a copy of ER and pushes it on ES.

error_pop_merge

This instruction takes the topmost entry of ES and merges the error status it contains with ES, making the result the new ES.

The merge is governed by four rules, with the merge result

1. Empty if both states are empty.

2. The non-empty state if only one of the two states is non-empty.

3. The state with the larger location, if the two states specify different locations.

4. The pair of the location shared by the two states, and the set-union of their messages for states at the same location.

error_nonterminal symbol

This is a guarded instruction. It does nothing if either ES is empty, or if the location in ES is not just past the last location saved in LS. Otherwise it sets the pair of that location and the nonterminal symbol as the new ES.

Note: In the above "just past" means "that location plus one", or also "the location of the next character after that location".

Status Control

The instructions in this section directly manipulate ST.

status_ok

This instruction sets ST to true, recording a success.

status_fail

This instruction sets ST to false, recording a failure.

status_negate

This instruction negates ST, turning a failure into a success and vice versa.

Location Handling

The instructions in this section access CL and LS.

loc_push

This instruction makes a copy of CL and pushes it on LS.

loc_pop_discard

This instructions pops the last saved location from LS.

loc_pop_rewind

This instruction pops the last saved location from LS and restores it as CL.

Nonterminal Execution

The instructions in this section access and manipulate NC.

symbol_restore symbol

This instruction checks if NC contains data for the nonterminal symbol at CL, or not. The result of the instruction is a boolean flag, with True indicating that data was found in the cache. In that case the instruction has further updated the architectural state of the machine with the cached information, namely CL, ST, ER, and SV.

The method with which the instruction's result is transformed into control flow is left undefined and the responsibility of the implementation.

symbol_save symbol

This instructions saves the current settings of CL, ST, ER, and SV in NC, using the pair of nonterminal symbol and the last location saved in LS as key.

Value Construction

The instructions in this section manipulate SV.

value_clear

This instruction clears SV.

value_leaf symbol

This instruction constructs an AST node for symbol covering the range of IN from one character after the last location saved on LS to CL and stores it in SV. ...

value_reduce symbol

This instruction generally behaves like value_nonterminal_leaf, except that it takes all AST nodes on ARS, if any, and makes them the children of the new node, with the last node saved on ARS becoming the right-most / last child. Note that ARS is not modfied by this operation.

AST Construction

The instructions in this section manipulate ARS and AS.

ast_value_push

This instruction makes a copy of SV and pushes it on ARS.

ast_push

This instruction pushes the current state of ARS on AS and then clears ARS.

ast_pop_rewind

This instruction pops the last entry saved on AS and restores it as the new state of ARS.

ast_pop_discard

This instruction pops the last entry saved on AS.

Control Flow

Normally this section would contain the specifications of the control flow instructions of the PARAM, i.e. (un)conditional jumps and the like. However, this part of the PARAM is intentionally left unspecified. This allows the implementations to freely choose how to implement control flow.

The implementation of this machine in Parser Tools, i.e the package pt::rde, is not only coded in Tcl, but also relies on Tcl commands to provide it with control flow (instructions).