To all interested,
The problem lies in using the conjunction & directly between the if
expression and the following expression.
If the If expression is surrounded by {} then the following expression
is evaluated when the if does not produce &fail
Hence
if test then { expression1} else { &fail } & expression2
doesn't evaluate the expression2 if test produces a result
however
{if test then { expression1} else {&fail}} & expression2
does evaluate expression2 when test succeeds
On 07/12/2010 03:50 PM, Bruce & Breeanna Rennie wrote:
> Ladies and Gentlemen,
>
> I am in the process of creating a PEG parser generator in Unicon. I have
> written some code that should be in a form that I can generate from
> other code.
>
> When the code is run, only the first part of the code is actually
> executed. From what I can see the next parts in the code should execute
> as it is using&
>
> The code is as follows
>
> procedure MatchComment()
> return {
> {
> # this is executed
> if found.Push(tab(match("#"))) then {
> {
> found.Pop()
> }
> write("First Part of MatchComment()")
> # the result returned is "First Part of MatchComment()"
> } else {
> write("FAIL")
> &fail
> }&
> {
> # this is not
> write("In MatchComment()")
> }&
> {
> while write({
> {
> if found.Push(not MatchEndOfLine()) then {
> {
> found.Pop()
> }
> } else {
> &fail
> }&
> if found.Push(MatchDOT()) then {
> {
> found.Pop()
> }
> } else {
> &fail
> }
> }
> }) do { }
> {
> &pos
> }
> }&
> if found.Push(MatchEndOfLine()) then {
> {
> found.Pop()
> }
> } else {
> &fail
> }
> }
> }
> end
>
>
> Does anyone see any problem with what is set up? I have run tracing and
> it shows that the only section outline above is being executed.
>
> The code is formatted this way to allow me to generate parsers from
> Templates for experimental purposes.
>
> regards
>
> Bruce Rennie
>
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