improved $1 (et al) error message plus updated rosetta stone

docs/parser/null-coalescing.md

@@ -41,13 +41,11 @@ The following extract was taken from [Wikipedia](https://en.wikipedia.org/wiki/N
 
 > The null coalescing operator (called the Logical Defined-Or operator in Perl)
 > is a binary operator that is part of the syntax for a basic conditional
-> expression in several programming languages, including C#, PowerShell as of
-> version 7.0.0, Perl as of version 5.10, Swift, and PHP 7.0.0. While its
-> behavior differs between implementations, the null coalescing operator
-> generally returns the result of its left-most operand if it exists and is not
-> null, and otherwise returns the right-most operand. This behavior allows a
-> default value to be defined for cases where a more specific value is not
-> available.
+> expression in several programming languages. While its behavior differs
+> between implementations, the null coalescing operator generally returns the
+> result of its left-most operand if it exists and is not null, and otherwise
+> returns the right-most operand. This behavior allows a default value to be
+> defined for cases where a more specific value is not available.
 >
 > In contrast to the ternary conditional if operator used as `x ? x : y`, but
 > like the binary Elvis operator used as `x ?: y`, the null coalescing operator

docs/user-guide/rosetta-stone.md

@@ -92,7 +92,7 @@ if you want to learn more about shell scripting in Murex.
 | [Assign a local variable](../commands/set.md) | `local foo="bar"` | `$foo = "bar"` [[2]](#footnotes) [[6]](#footnotes)<br/><br/>`out "bar" \| set $foo` |
 | [Assign a global variable](../commands/global.md) | `foo="bar"` | `$GLOBAL.foo = "bar"` [[6]](#footnotes)<br/><br/>`out "bar" \| global $foo` |
 | [Assign an environmental variable](../commands/export.md) | `export foo="bar"` | `export foo = "bar"` [[1]](#footnotes) [[2]](#footnotes) [[3]](#footnotes)<br/><br/>`$ENV.foo = "bar"` [[6]](#footnotes)<br/><br/>`out "bar" \| export $foo` [[3]](#footnotes) |
-| [Assign with a default value](../parser/null-coalescing.md) | `FOOBAR="${VARIABLE:-default}"` | `$foobar = $variable ?: "default"` <br/><br/> (the elvis operator can be used in any part of expressions and just for assignments)
+| [Assign with a default value](../parser/null-coalescing.md) | `FOOBAR="${VARIABLE:-default}"` | `$foobar = $variable ?? "default"` |
 
 ### Arrays
 (eg arrays, lists)

gen/parser/null_coalescing_op_doc.yaml

@@ -36,13 +36,11 @@
     
     > The null coalescing operator (called the Logical Defined-Or operator in Perl)
     > is a binary operator that is part of the syntax for a basic conditional
-    > expression in several programming languages, including C#, PowerShell as of
-    > version 7.0.0, Perl as of version 5.10, Swift, and PHP 7.0.0. While its
-    > behavior differs between implementations, the null coalescing operator
-    > generally returns the result of its left-most operand if it exists and is not
-    > null, and otherwise returns the right-most operand. This behavior allows a
-    > default value to be defined for cases where a more specific value is not
-    > available.
+    > expression in several programming languages. While its behavior differs
+    > between implementations, the null coalescing operator generally returns the
+    > result of its left-most operand if it exists and is not null, and otherwise
+    > returns the right-most operand. This behavior allows a default value to be
+    > defined for cases where a more specific value is not available.
     >
     > In contrast to the ternary conditional if operator used as `x ? x : y`, but
     > like the binary Elvis operator used as `x ?: y`, the null coalescing operator

gen/user-guide/rosetta-stone.inc.md

@@ -88,7 +88,7 @@ if you want to learn more about shell scripting in Murex.
 | [Assign a local variable](../commands/set.md) | `local foo="bar"` | `$foo = "bar"` [[2]](#footnotes) [[6]](#footnotes)<br/><br/>`out "bar" \| set $foo` |
 | [Assign a global variable](../commands/global.md) | `foo="bar"` | `$GLOBAL.foo = "bar"` [[6]](#footnotes)<br/><br/>`out "bar" \| global $foo` |
 | [Assign an environmental variable](../commands/export.md) | `export foo="bar"` | `export foo = "bar"` [[1]](#footnotes) [[2]](#footnotes) [[3]](#footnotes)<br/><br/>`$ENV.foo = "bar"` [[6]](#footnotes)<br/><br/>`out "bar" \| export $foo` [[3]](#footnotes) |
-| [Assign with a default value](../parser/null-coalescing.md) | `FOOBAR="${VARIABLE:-default}"` | `$foobar = $variable ?: "default"` <br/><br/> (the elvis operator can be used in any part of expressions and just for assignments)
+| [Assign with a default value](../parser/null-coalescing.md) | `FOOBAR="${VARIABLE:-default}"` | `$foobar = $variable ?? "default"` |
 
 ### Arrays
 (eg arrays, lists)

lang/variables.go

@@ -36,7 +36,7 @@ func errVarCannotUpdateIndexOrElement(name string) error {
 }
 
 func errVarNoParam(i int, err error) error {
-	return fmt.Errorf("variable '%d' cannot be defined: %s", i, err.Error())
+	return fmt.Errorf("variable '%d' is not set because the scope returned the following error when querying parameter %d: %s", i, i, err.Error())
 }
 
 func errVarZeroLengthPath(name string) error {