Allow user to terminate the parser - close #13

assets/parser.c.erb

@@ -21,6 +21,7 @@
 #define P_UNEXPECTED_TOKEN 3u
 #define P_DROP 4u
 #define P_EOF 5u
+#define P_USER_TERMINATED 6u
 <% end %>
 
 /* An invalid ID value. */
@@ -737,12 +738,13 @@ static void state_values_stack_free(state_values_stack_t * stack)
  *
  * @param rule The ID of the rule.
  *
- * @return Parse value.
+ * @retval P_SUCCESS
+ *   Continue parsing.
+ * @retval P_USER_TERMINATED
+ *   User requested to terminate parsing.
  */
-static <%= @grammar.prefix %>value_t parser_user_code(uint32_t rule, state_values_stack_t * statevalues, uint32_t n_states)
+static size_t parser_user_code(<%= @grammar.prefix %>value_t * _pvalue, uint32_t rule, state_values_stack_t * statevalues, uint32_t n_states, <%= @grammar.prefix %>context_t * context)
 {
-    <%= @grammar.prefix %>value_t _pvalue = {0};
-
     switch (rule)
     {
 <% @grammar.rules.each do |rule| %>
@@ -755,7 +757,7 @@ static <%= @grammar.prefix %>value_t parser_user_code(uint32_t rule, state_value
     default: break;
     }
 
-    return _pvalue;
+    return P_SUCCESS;
 }
 
 /**
@@ -888,7 +890,12 @@ size_t <%= @grammar.prefix %>parse(<%= @grammar.prefix %>context_t * context)
         if (reduce_index != INVALID_ID)
         {
             /* We have something to reduce. */
-            reduced_parser_value = parser_user_code(parser_reduce_table[reduce_index].rule, &statevalues, parser_reduce_table[reduce_index].n_states);
+            <%= @grammar.prefix %>value_t reduced_parser_value2 = {0};
+            if (parser_user_code(&reduced_parser_value2, parser_reduce_table[reduce_index].rule, &statevalues, parser_reduce_table[reduce_index].n_states, context) == P_USER_TERMINATED)
+            {
+                return P_USER_TERMINATED;
+            }
+            reduced_parser_value = reduced_parser_value2;
             reduced_rule_set = parser_reduce_table[reduce_index].rule_set;
             state_values_stack_pop(&statevalues, parser_reduce_table[reduce_index].n_states);
             continue;
@@ -933,3 +940,16 @@ size_t <%= @grammar.prefix %>parse(<%= @grammar.prefix %>context_t * context)
 {
     return context->text_position;
 }
+
+/**
+ * Get the user terminate code.
+ *
+ * @param context
+ *   Lexer/parser context structure.
+ *
+ * @return User terminate code.
+ */
+size_t <%= @grammar.prefix %>user_terminate_code(<%= @grammar.prefix %>context_t * context)
+{
+    return context->user_terminate_code;
+}

assets/parser.d.erb

@@ -27,6 +27,7 @@ public enum : size_t
     <%= @grammar.prefix.upcase %>UNEXPECTED_TOKEN,
     <%= @grammar.prefix.upcase %>DROP,
     <%= @grammar.prefix.upcase %>EOF,
+    <%= @grammar.prefix.upcase %>USER_TERMINATED,
 }
 
 /** Token type. */
@@ -114,6 +115,9 @@ public struct <%= @grammar.prefix %>context_t
 
     /** Unexpected token received. */
     <%= @grammar.prefix %>token_t token;
+
+    /** User terminate code. */
+    size_t user_terminate_code;
 }
 
 /**************************************************************************
@@ -141,6 +145,7 @@ private enum : size_t
     P_UNEXPECTED_TOKEN,
     P_DROP,
     P_EOF,
+    P_USER_TERMINATED,
 }
 <% end %>
 
@@ -761,12 +766,13 @@ private immutable parser_state_t[] parser_state_table = [
  *
  * @param rule The ID of the rule.
  *
- * @return Parse value.
+ * @retval P_SUCCESS
+ *   Continue parsing.
+ * @retval P_USER_TERMINATED
+ *   User requested to terminate parsing.
  */
-private <%= @grammar.prefix %>value_t parser_user_code(uint rule, state_value_t[] statevalues, uint n_states)
+private size_t parser_user_code(<%= @grammar.prefix %>value_t * _pvalue, uint rule, state_value_t[] statevalues, uint n_states, <%= @grammar.prefix %>context_t * context)
 {
-    <%= @grammar.prefix %>value_t _pvalue;
-
     switch (rule)
     {
 <% @grammar.rules.each do |rule| %>
@@ -779,7 +785,7 @@ private <%= @grammar.prefix %>value_t parser_user_code(uint rule, state_value_t[
     default: break;
     }
 
-    return _pvalue;
+    return P_SUCCESS;
 }
 
 /**
@@ -906,7 +912,12 @@ public size_t <%= @grammar.prefix %>parse(<%= @grammar.prefix %>context_t * cont
         if (reduce_index != INVALID_ID)
         {
             /* We have something to reduce. */
-            reduced_parser_value = parser_user_code(parser_reduce_table[reduce_index].rule, statevalues, parser_reduce_table[reduce_index].n_states);
+            <%= @grammar.prefix %>value_t reduced_parser_value2;
+            if (parser_user_code(&reduced_parser_value2, parser_reduce_table[reduce_index].rule, statevalues, parser_reduce_table[reduce_index].n_states, context) == P_USER_TERMINATED)
+            {
+                return P_USER_TERMINATED;
+            }
+            reduced_parser_value = reduced_parser_value2;
             reduced_rule_set = parser_reduce_table[reduce_index].rule_set;
             statevalues.length -= parser_reduce_table[reduce_index].n_states;
             continue;
@@ -948,3 +959,16 @@ public <%= @grammar.prefix %>position_t <%= @grammar.prefix %>position(<%= @gram
 {
     return context.text_position;
 }
+
+/**
+ * Get the user terminate code.
+ *
+ * @param context
+ *   Lexer/parser context structure.
+ *
+ * @return User terminate code.
+ */
+public size_t <%= @grammar.prefix %>user_terminate_code(<%= @grammar.prefix %>context_t * context)
+{
+    return context.user_terminate_code;
+}

assets/parser.h.erb

@@ -20,6 +20,7 @@
 #define <%= @grammar.prefix.upcase %>UNEXPECTED_TOKEN 3u
 #define <%= @grammar.prefix.upcase %>DROP 4u
 #define <%= @grammar.prefix.upcase %>EOF 5u
+#define <%= @grammar.prefix.upcase %>USER_TERMINATED 6u
 
 /** Token type. */
 typedef <%= get_type_for(@grammar.invalid_token_id) %> <%= @grammar.prefix %>token_t;
@@ -109,6 +110,9 @@ typedef struct
 
     /** Unexpected token received. */
     <%= @grammar.prefix %>token_t token;
+
+    /** User terminate code. */
+    size_t user_terminate_code;
 } <%= @grammar.prefix %>context_t;
 
 void <%= @grammar.prefix %>context_init(<%= @grammar.prefix %>context_t * context, uint8_t const * input, size_t input_length);
@@ -123,3 +127,5 @@ size_t <%= @grammar.prefix %>parse(<%= @grammar.prefix %>context_t * context);
 <%= start_rule_type[1] %> <%= @grammar.prefix %>result(<%= @grammar.prefix %>context_t * context);
 
 <%= @grammar.prefix %>position_t <%= @grammar.prefix %>position(<%= @grammar.prefix %>context_t * context);
+
+size_t <%= @grammar.prefix %>user_terminate_code(<%= @grammar.prefix %>context_t * context);

doc/user_guide.md

@@ -13,7 +13,7 @@ Propane is a LALR Parser Generator (LPG) which:
   * generates a built-in lexer to tokenize input
   * supports UTF-8 lexer inputs
   * generates a table-driven shift/reduce parser to parse input in linear time
-  * target C or D language outputs
+  * targets C or D language outputs
   * is MIT-licensed
   * is distributable as a standalone Ruby script
 
@@ -574,6 +574,31 @@ default.
 It can also be used when generating multiple lexers/parsers to be used in the
 same program to avoid symbol collisions.
 
+##> User termination of the parser
+
+Propane supports allowing parser user code blocks to terminate execution of the
+parser.
+One example use of this functionality is to detect and report an error before
+the parser continues parsing the remainder of the input.
+Another use of this features is to begin parsing input and determine whether a
+different parser should be used instead.
+
+To terminate parsing from a parser user code block, use the `$terminate(code)`
+function, passing an integer expression argument.
+For example:
+
+```
+NewExpression -> new Expression <<
+  $terminate(42);
+>>
+```
+
+The value passed to the `$terminate()` function is known as the "user terminate
+code".
+If the parser returns a `P_USER_TERMINATED` result code, then the user
+terminate code can be accessed using the `p_user_terminate_code()` API
+function.
+
 #> License
 
 Propane is licensed under the terms of the MIT License:

lib/propane/generator.rb

@@ -200,8 +200,13 @@ class Propane
       end
       if parser
         code = code.gsub(/\$\$/) do |match|
+          case @language
+          when "c"
+            "_pvalue->v_#{rule.ptypename}"
+          when "d"
             "_pvalue.v_#{rule.ptypename}"
           end
+        end
         code = code.gsub(/\$(\d+)/) do |match|
           index = $1.to_i
           case @language
@@ -211,6 +216,15 @@ class Propane
             "statevalues[$-1-n_states+#{index}].pvalue.v_#{rule.components[index - 1].ptypename}"
           end
         end
+        code = code.gsub(/\$terminate\((.*)\);/) do |match|
+          user_terminate_code = $1
+          case @language
+          when "c"
+            "context->user_terminate_code = (#{user_terminate_code}); return P_USER_TERMINATED;"
+          when "d"
+            "context.user_terminate_code = (#{user_terminate_code}); return P_USER_TERMINATED;"
+          end
+        end
       else
         code = code.gsub(/\$\$/) do |match|
           case @language

spec/propane_spec.rb

@@ -729,6 +729,26 @@ EOF
         expect(results.stderr).to eq ""
         expect(results.status).to eq 0
       end
+
+      it "allows the user to terminate the parser" do
+        write_grammar <<EOF
+token a;
+token b;
+token c;
+Start -> Any;
+Any -> a Any;
+Any -> b Any <<
+  $terminate(4200);
+>>
+Any -> c Any;
+Any -> ;
+EOF
+        build_parser(language: language)
+        compile("spec/test_user_terminate.#{language}", language: language)
+        results = run
+        expect(results.stderr).to eq ""
+        expect(results.status).to eq 0
+      end
     end
   end
 end

spec/test_user_terminate.c

@@ -0,0 +1,19 @@
+#include "testparser.h"
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+int main()
+{
+    char const * input = "aacc";
+    p_context_t context;
+    p_context_init(&context, (uint8_t const *)input, strlen(input));
+    assert(p_parse(&context) == P_SUCCESS);
+
+    input = "abc";
+    p_context_init(&context, (uint8_t const *)input, strlen(input));
+    assert(p_parse(&context) == P_USER_TERMINATED);
+    assert(p_user_terminate_code(&context) == 4200);
+
+    return 0;
+}

spec/test_user_terminate.d

@@ -0,0 +1,20 @@
+import testparser;
+import std.stdio;
+
+int main()
+{
+    return 0;
+}
+
+unittest
+{
+    string input = "aacc";
+    p_context_t context;
+    p_context_init(&context, input);
+    assert(p_parse(&context) == P_SUCCESS);
+
+    input = "abc";
+    p_context_init(&context, input);
+    assert(p_parse(&context) == P_USER_TERMINATED);
+    assert(p_user_terminate_code(&context) == 4200);
+}