[examples] write expressions intro example

bin/build_examples.sh

@@ -11,6 +11,10 @@ bin/bld_core.sh show_ctx
 
 examps="examples"
 
+bin/bld_core.sh unit expr_intro     $examps/expr/expr_intro.c
+
+exit
+
 bin/bld_core.sh unit hello_world    $examps/intro/hello_world.c
 bin/bld_core.sh unit parse_check    $examps/intro/parse_check.c
 bin/bld_core.sh unit data_desk_like $examps/intro/data_desk_like_template.c

bin/run_examples.sh

@@ -8,6 +8,12 @@ root_path=$PWD
 build_path=$root_path/build
 examps=$root_path/examples
 
+echo ~~~ Running Expression Intro ~~~
+$build_path/expr_intro.exe $examps/expr/expr_intro.mdesk
+echo
+
+exit
+
 echo ~~~ Running Type Metadata Generator Example ~~~
 cd $examps/type_metadata/generated
 $build_path/type_metadata.exe $examps/type_metadata/types.mdesk

examples/expr/expr_intro.c

@@ -14,10 +14,39 @@ static MD_Arena *arena = 0;
 
 //~ expression setup and helpers //////////////////////////////////////////////
 
+enum
+{
+    OpAdd,
+    OpMul,
+};
+
 void
 print_expression(FILE *out, MD_Expr *expr)
 {
-    // TODO(allen): finish
+    MD_ExprOpr *op = expr->op;
+    if (op == 0)
+    {
+        MD_Node *node = expr->md_node;
+        if (node->raw_string.size != 0 &&
+            MD_NodeIsNil(node->first_child))
+        {
+            fprintf(out, "%.*s", MD_S8VArg(node->raw_string));
+        }
+        else
+        {
+            MD_CodeLoc loc = MD_CodeLocFromNode(node);
+            MD_PrintMessage(stderr, loc, MD_MessageKind_Error,
+                            MD_S8Lit("the expression system does not expect this kind of node"));
+        }
+    }
+    else
+    {
+        fprintf(out, "(");
+        print_expression(out, expr->left);
+        fprintf(out, " %.*s ", MD_S8VArg(op->string));
+        print_expression(out, expr->right);
+        fprintf(out, ")");
+    }
 }
 
 
@@ -82,7 +111,7 @@ int main(int argc, char **argv)
             }
             
             // print the expression
-            fprintf(stdout, "%s = ");
+            fprintf(stdout, "%.*s = ", MD_S8VArg(node->string));
             print_expression(stdout, parse.expr);
             fprintf(stdout, ";\n");
         }

tests/expression_tests.c

@@ -160,9 +160,11 @@ static void parenthesize_exclude_outer(MD_Arena *arena, OperatorDescription *des
                MD_S8Match(op_s, MD_S8Lit("{}"), 0) || MD_S8Match(op_s, MD_S8Lit("[)"), 0) || 
                MD_S8Match(op_s, MD_S8Lit("(]"), 0))
             {
-                MD_S8ListPush(arena, l, MD_S8Substring(op_s, 0, 1));
+                MD_u8 buf[5];
-                MD_S8ListPush(arena, l, MD_S8Lit("..."));
+                buf[0] = op_s.str[0];
-                MD_S8ListPush(arena, l, MD_S8Substring(op_s, 1, 2));
+                buf[1] = buf[2] = buf[3] = '.';
+                buf[4] = op_s.str[1];
+                MD_S8ListPush(arena, l, MD_S8(buf, sizeof(buf)));
             }
             else
             {