Accessing Input Elements

When dealing with complex input formats, attaching constraints can be complex, as elements can occur multiple times in a generated input. Fandango offers a few mechanisms to disambiguate these, and to specify specific contexts in which to search for elements.

Derivation Trees

So far, we have always assumed that Fandango generates strings from the grammar. Behind the scenes, though, Fandango creates a far richer data structure - a so-called derivation tree that maintains the structure of the string and allows accessing individual elements. Every time Fandango sees a grammar rule

<symbol> ::= ...

it generates a derivation tree whose root is <symbol> and whose children are the elements of the right-hand side of the rule.

Let’s have a look at our persons.fan spec:

<start> ::= <person_name> "," <age>
<person_name> ::= <first_name> " " <last_name>
<first_name> ::= <name>
<last_name> ::= <name>
<name> ::= <ascii_uppercase_letter><ascii_lowercase_letter>+
<age> ::= <digit>+

The <start> rule says

<start> ::= <person_name> "," <age>

Then, a resulting derivation tree for <start> looks like this:

As Fandango expands more and more symbols, it expands the derivation tree accordingly. Since the grammar definition for <person_name> says

<person_name> ::= <first_name> " " <last_name>

the above derivation tree would be extended to

And if we next extend <age> and then <digit> based on their definitions

<age> ::= <digit>+

If one has a Kleene operator like +, *, or ?, the elements operated on become children of the symbol being defined. Hence, the <digit> elements become children of the <age> symbol.

our tree gets to look like this:

Repeating the process, it thus obtains a tree like this:

Note how the tree records the entire history of how it was created - how it was derived, actually.

To obtain a string from the tree, we traverse its children left-to-right, ignoring all nonterminal symbols (in <...>) and considering only the terminal symbols (in quotes). This is what we get for the above tree:

Ex Pltz,18

And this is the string Fandango produces. However, viewing the Fandango results as derivation trees allows us to access elements of the Fandango-produced strings and to express constraints on them.

Diagnosing Derivation Trees

To examine the derivation trees that Fandango produces, use the --format=grammar output format. This produces the output in a grammar-like format, where children are indented under their respective parents. As an example, here is how to print a derivation tree from persons.fan:

$ fandango fuzz -f persons.fan -n 1 --format=grammar

<start> ::= <person_name> ',' <age>  # Position 0x0000 (0); Hqwlsxsvunuqlykmguykt Yxvrkmdcyviqthymndxy,6053337261160
  <person_name> ::= <first_name> ' ' <last_name>  # Position 0x0001 (1); Hqwlsxsvunuqlykmguykt Yxvrkmdcyviqthymndxy
    <first_name> ::= <name>
      <name> ::= <ascii_uppercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter>  # Hqwlsxsvunuqlykmguykt
        <ascii_uppercase_letter> ::= <_ascii_uppercase_letter>
          <_ascii_uppercase_letter> ::= 'H'  # Position 0x0002 (2)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'q'  # Position 0x0003 (3)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'w'  # Position 0x0004 (4)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'l'  # Position 0x0005 (5)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 's'  # Position 0x0006 (6)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'x'  # Position 0x0007 (7)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 's'  # Position 0x0008 (8)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'v'  # Position 0x0009 (9)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'u'  # Position 0x000a (10)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'n'  # Position 0x000b (11)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'u'  # Position 0x000c (12)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'q'  # Position 0x000d (13)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'l'  # Position 0x000e (14)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'y'  # Position 0x000f (15)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'k'  # Position 0x0010 (16)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'm'  # Position 0x0011 (17)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'g'  # Position 0x0012 (18)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'u'  # Position 0x0013 (19)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'y'  # Position 0x0014 (20)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'k'  # Position 0x0015 (21)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 't'  # Position 0x0016 (22)
    <last_name> ::= <name>
      <name> ::= <ascii_uppercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter> <ascii_lowercase_letter>  # Yxvrkmdcyviqthymndxy
        <ascii_uppercase_letter> ::= <_ascii_uppercase_letter>
          <_ascii_uppercase_letter> ::= 'Y'  # Position 0x0017 (23)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'x'  # Position 0x0018 (24)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'v'  # Position 0x0019 (25)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'r'  # Position 0x001a (26)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'k'  # Position 0x001b (27)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'm'  # Position 0x001c (28)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'd'  # Position 0x001d (29)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'c'  # Position 0x001e (30)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'y'  # Position 0x001f (31)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'v'  # Position 0x0020 (32)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'i'  # Position 0x0021 (33)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'q'  # Position 0x0022 (34)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 't'  # Position 0x0023 (35)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'h'  # Position 0x0024 (36)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'y'  # Position 0x0025 (37)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'm'  # Position 0x0026 (38)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'n'  # Position 0x0027 (39)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'd'  # Position 0x0028 (40)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'x'  # Position 0x0029 (41)
        <ascii_lowercase_letter> ::= <_ascii_lowercase_letter>
          <_ascii_lowercase_letter> ::= 'y'  # Position 0x002a (42)
  <age> ::= <digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit>  # 6053337261160
    <digit> ::= <_digit>
      <_digit> ::= '6'  # Position 0x002b (43)
    <digit> ::= <_digit>
      <_digit> ::= '0'  # Position 0x002c (44)
    <digit> ::= <_digit>
      <_digit> ::= '5'  # Position 0x002d (45)
    <digit> ::= <_digit>
      <_digit> ::= '3'  # Position 0x002e (46)
    <digit> ::= <_digit>
      <_digit> ::= '3'  # Position 0x002f (47)
    <digit> ::= <_digit>
      <_digit> ::= '3'  # Position 0x0030 (48)
    <digit> ::= <_digit>
      <_digit> ::= '7'  # Position 0x0031 (49)
    <digit> ::= <_digit>
      <_digit> ::= '2'  # Position 0x0032 (50)
    <digit> ::= <_digit>
      <_digit> ::= '6'  # Position 0x0033 (51)
    <digit> ::= <_digit>
      <_digit> ::= '1'  # Position 0x0034 (52)
    <digit> ::= <_digit>
      <_digit> ::= '1'  # Position 0x0035 (53)
    <digit> ::= <_digit>
      <_digit> ::= '6'  # Position 0x0036 (54)
    <digit> ::= <_digit>
      <_digit> ::= '0'  # Position 0x0037 (55)

We see how the produced derivation tree consists of a <start> symbol, whose <first_name> and <last_name> children expand into <name> and letters; the <age> symbol expands into <digit> symbols.

The comments (after #) show the individual positions into the input, as well as the values of compound symbols.

What is the full string represented by the above derivation tree?

Solution

You can find on the right-hand side of the first line.

Tip

The --format=grammar option is great for debugging, especially binary formats.

Specifying Paths

One effect of Fandango producing derivation trees rather than “just” strings is that we can define special operators that allow us to access subtrees (or sub-elements) of the produced strings - and express constraints on them. This is especially useful if we want constraints to apply only in specific contexts - say, as part of some element <a>, but not as part of an element <b>.

Accessing Children

These selectors are similar to XPath, but better aligned with Python. In XPath, the first child has the index 1, in Fandango, it has the index 0.

The expression <foo>[N] accesses the N-th child of <foo>, starting with zero.

If <foo> is defined in the grammar as

<foo> ::= <bar> ":" <baz>

then <foo>[0] returns the <bar> element, <foo>[1] returns ":", and <foo>[2] returns the <baz> element.

In our persons.fan derivation tree for Ex Pltz, for instance, <start>[0] would return the <person_name> element ("Ex Pltz"), and <start>[2] would return the <age> element (18).

We can use this to access elements in specific contexts. For instance, if we want to refer to a <name> element, but only if it is the child of a <first_name> element, we can refer to it as <first_name>[0] - the first child of a <first_name> element:

<first_name> ::= <name>

Here is a constraint that makes Fandango produce first names that end with x:

Since a <first_name> is defined to be a <name>, we could also write <first_name>.endswith("x")

$ fandango fuzz -f persons.fan -n 10 -c '<first_name>[0].endswith("x")'

Rtxinsdtygjbrqpjcpqx Xlmfdry,8382011480
Udzliiouuqex Bqjmrsgvscioapns,03783

Quxsuvynfjomwfkjax Pozhmcqu,4619
Bvxdamtx Hmteumhuwamulhuh,63

Sdategmydkralahx Kfzakcwjn,43109471964015140

Khbwlfahnwevrpptfux Dcflim,39147825

Udzliiouuqex Hqjmrsgvscioapns,03783
Bvxdamtx Bmteumhuwamulhuh,63
Sdategmydkralahx Rz,0075

Rtxinsdtygjbrqpjcpqx Dt,8382011480

Tip

As in Python, you can use negative indexes to refer to the last elements. <age>[-1], for instance, gives you the last child of an <age> subtree.

Important

While symbols act as strings in many contexts, this is where they differ. To access the first character of a symbol <foo>, you need to explicitly convert it to a string first, as in str(<foo>)[0].

Slices

The Fandango slices maintain the property that <name>[n:m] = <name>[n] + <name>[n + 1] + … + <name>[m - 1], which holds for all sequences in Python.

Fandango also allows you to use Python slice syntax to access multiple children at once. <name>[n:m] returns a new (unnamed) root which has <name>[n], <name>[n + 1], …, <name>[m - 1] as children. This is useful, for instance, if you want to compare several children against a string:

$ fandango fuzz -f persons-faker.fan -n 10 -c '<name>[0:2] == "Ch"'

Chelsey Chavez,817047743013

Christopher Chavez,817047743013

Chelsey Chavez,017047743013

Christopher Chavez,817047743713
Christopher Chavez,229821850

Chelsey Chavez,14589265851665

Christopher Chavez,2248833558398
Chad Chavez,817047743713

Chelsey Chavez,817347743013

Christopher Chavez,2248833558998

Would one also be able to use <start>[0:2] == "Ch" to obtain inputs that all start with "Ch"?

Solution

No, this would not work. Remember that in derivation trees, indexes refer to children, not characters. So, according to the rule

<start> ::= <person_name> "," <age>

<start>[0] is a <person_name>, <start>[1] is a ",", and <start>[2] is an <age>. Hence, <start>[0:2] refers to <start> itself, which cannot be "Ch".

Indeed, to have the string start with "Ch", you (again) need to convert <start> into a string first, and then access its individual characters:

$ fandango fuzz -f persons-faker.fan -n 10 -c 'str(<start>)[0:2] == "Ch"'

Christina Hunter,43

Christine Williams,8

Chelsea Shaw,8624781497258162967

Chad Maynard,323

Charles Marshall,1847288087607827705

Chad Long,15344097133533118

Christine Johnson,255244892114
Christine Shaw,8
Chelsea Williams,8624781497258162967
Christina Knox,79244045

The Fandango slices maintain the property that <name>[i:] + <name>[:i] = <name>

Fandango supports the full Python slice semantics:

• An omitted first index defaults to zero, so <foo>[:2] returns the first two children.

• An omitted second index defaults to the size of the string being sliced, so <foo>[2:] returns all children starting with <foo>[2].

• Both the first and the second index can be negative again.

Selecting Children

Referring to children by number, as in <foo>[0], can be a bit cumbersome. This is why in Fandango, you can also refer to elements by name.

In XPath, the corresponding operator is /.

The expression <foo>.<bar> allows accessing elements <bar> when they are a direct child of a symbol <foo>. This requires that <bar> occurs in the grammar rule defining <foo>:

<foo> ::= ...some expansion that has <bar>...

To refer to the <name> element as a direct child of a <first_name> element, you thus write <first_name>.<name>. This allows you to express the earlier constraint in a possibly more readable form:

$ fandango fuzz -f persons.fan -n 10 -c '<first_name>.<name>.endswith("x")'

Ttx Dga,0

Ttx Dga,36837118380

Dihwntfpbfttnx Tzpbnvqdfzcxfpidnkx,006179

Ttx Dga,7
Ttx Dga,8

Ttx Dga,46384713954338988

Jihwntfpbfttnx Tzpbnvqdfzcxfpidnkx,006179

Ttx Tzpbnvqdfzcxfpidnkx,006179
Dihwntfpbfttnx Dga,36837118380
Dihwntfpbfttnx Jhjjtaz,006179

Note

You can only access nonterminal children this way; <person_name>." " (the space in the <person_name>) gives an error.

Selecting Descendants

Often, you want to refer to elements in a particular context set by the enclosing element. This is why in Fandango, you can also refer to descendants.

In XPath, the corresponding operator is //.

The expression <foo>..<bar> allows accessing elements <bar> when they are a descendant of a symbol <foo>. <bar> is a descendant of <foo> if

<foo>..<bar> includes <foo>.<bar>.

• <bar> is a child of <foo>; or

• one of <foo>’s children has <bar> as a descendant.

If that sounds like a recursive definition, that is because it is. A simpler way to think about <foo>..<bar> may be “All <bar>s that occur within <foo>”.

Let us take a look at some rules in our persons.fan example:

<first_name> ::= <name>
<last_name> ::= <name>
<name> ::= <ascii_uppercase_letter><ascii_lowercase_letter>+
<ascii_uppercase_letter> ::= "A" | "B" | "C" | ... | "Z"

To refer to all <ascii_uppercase_letter> element as descendant of a <first_name> element, you thus write <first_name>..<ascii_uppercase_letter>.

Hence, to make all uppercase letters X, but only as part of a first name, you may write

$ fandango fuzz -f persons.fan -n 10 -c '<first_name>..<ascii_uppercase_letter> == "X"'

Xwzgnryvuhqshejv Ljocxrjlujmqnydycmohc,82080850252596836
Xkvf Abfhdbytj,83159653155041267

Xsipvveprtejkpvjntwhd At,9187575027
Xbne Vqdrpccykwgoym,2090846
Xknnauwdnhsuzcunuzzsy Zppuicvdrjfamizd,008522599773139

Xxwyvcewqg Ilkoarirbmouzmnk,29591741326841173423
Xzznbxd Sw,7442062330

Xumesyfjlyiaaaincs Tqygnztenhru,0465685574086549
Xsiprrzp Lzh,37
Xokelcbgvuuiowrbrbim Siadumrbr,1864101759852

Chains

You can freely combine [], ., and .. into chains that select subtrees. What would the expression <start>[0].<last_name>..<ascii_lowercase_letter> refer to, for instance?

Solution

This is easy:

• <start>[0] is the first element of start, hence a <person_name>.

• .<last_name> refers to the child of type <last_name>

• ..<ascii_lowercase_letter> refers to all descendants of type <ascii_lowercase_letter>

Let’s use this in a constraint:

$ fandango fuzz -f persons.fan -n 10 -c '<start>[0].<last_name>..<ascii_lowercase_letter> == "x"'

Beyigicagmytarrnr Pxxxxxxxxxxxxxxxx,2292232884828150588

Nxgakwt Axxxxxxxxxxxxxxxxxx,797000620334951661
Iyuyodmtkgpbab Oxxxx,2963166630708
Nv Wxxxxxx,261349911

Gndtopkvpk Kxxxxxxxxxxxxx,0999672971603
Hhlnjmqv Xxxxxxxx,30282737655576008891

Qdgrihvab Zxxxxxxxxxxxxxxxxxx,057248574142136
Juyw Lxxxxxxxxxxx,1947039725
Dolisxi Yxxxxxxxxxx,85925070165599

Nenkvuzzwuinz Hxxxxxxx,010

Quantifiers

By default, whenever you use a symbol <foo> in a constraint, this constraint applies to all occurrences of <foo> in the produced output string. For your purposes, though, one such instance already may suffice. This is why Fandango allows expressing quantification in constraints.

Star Expressions

In Fandango, you can prefix an element with * to obtain a collection of all these elements within an individual string. Hence, *<name> is a collection of all <name> elements within the generated string. This syntax can be used in a variety of ways. For instance, we can have a constraint check whether a particular element is in the collection:

Not every constraint that can be expressed also can be solved by Fandango.

"Pablo" in *<name>

This constraint evaluates to True if any of the values in *<name> (= one of the two <name> elements) is equal to "Pablo". *-expressions are mostly useful in quantifiers, which we discuss below.

Existential Quantification

To express that within a particular scope, at least one instance of a symbol must satisfy a constraint, use a *-expression in combination with any():

any(CONSTRAINT for ELEM in *SCOPE)

where

• SCOPE is a nonterminal (e.g. <age>);

• ELEM is a Python variable; and

• CONSTRAINT is a constraint over ELEM

Hence, the expression

any(n.startswith("A") for n in *<name>)

ensures there is at least one element <name> that starts with an “A”:

Let us decompose this expression for a moment:

• The expression for n in *<name> lets Python iterate over *<name> (all <name> objects within a person)…

• … and evaluate n.startswith("A") for each of them, resulting in a collection of Boolean values.

• The Python function any(list) returns True if at least one element in list is True.

So, what we get is existential quantification:

$ fandango fuzz -f persons.fan -n 10 -c 'any(n.startswith("A") for n in *<name>)'

Jfsbwejxuv Arm,455

Pmznvbquakwsm Abcfc,67511639201791680578

Lkjsnufgeibykm Ayvtuulqxdwhiiodnndz,3747021953833882

Xuglfozpapyem Acnsjz,9099026
Avgayuiqsviwm Afu,34825819783004

Atcmfhpuwyssh Cknxgaeq,24240614507295626

Adiwltbrbheqhrayj Adderuoitz,518164160

Mfumzyheouqsipgr Alylyn,89116482000460300706

Xpfo Advafqmqpcwzydosgug,0335947

Assjaqoyyvshrxb Dlvatjfubxtkb,6674439171526333

Universal Quantification

Where there are existential quantifiers, there also are universal quantifiers. Here we use the Python all() function; all(list) evaluates to True only if all elements in list are True.

We use a *-expression in combination with all():

all(CONSTRAINT for ELEM in *SCOPE)

Hence, the expression

all(c == "a" for c in *<first_name>..<ascii_lowercase_letter>)

ensures that all sub-elements <ascii_lowercase_letter> in <first_name> have the value “a”.

Again, let us decompose this expression:

• The expression for c in *<first_name>..<ascii_lowercase_letter> lets Python iterate over all <ascii_lowercase_letter> objects within <first_name>…

• … and evaluate c == "a" for each of them, resulting in a collection of Boolean values.

• The Python function all(list) returns True if all elements in list are True.

So, what we get is universal quantification:

$ fandango fuzz -f persons.fan -n 10 -c 'all(c == "a" for c in *<first_name>..<ascii_lowercase_letter>)'

Iaaaaaaaaaa Wtdlftepkasx,93888904761
Zaaa Buoowaparfjcbmhqfzjxm,0893164703159444236
Xaaaa Tnycdu,0592306638499783

Vaaaaa Dvhijtxedkj,7760524
Qaaaaaaaaaaaaaaaaa Otncnkflrvlhjciqnak,8547977738236549

Qa Bghoxczndkv,03648344
Vaaaa Fr,61713973550
Raaaaaaaaaaaaaaaaaa Prbyyiyzchxphyruct,42014

Caaaaaaaa Zrfgackhdlzcnicjjxfxr,668
Haaaa Jwfbspztakv,23524998152087

By default, all symbols are universally quantified within <start>, so a dedicated universal quantifier is only needed if you want to limit the scope to some sub-element. This is what we do here with <first_name>..<ascii_lowercase_letter>, limiting the scope to <first_name>.

Given the default universal quantification, you can actually achieve the same effect as above without all() and without a *. How?

Solution

You can access all <ascii_lowercase_letter> elements within <first_name> directly:

$ fandango fuzz -f persons.fan -n 10 -c '<first_name>..<ascii_lowercase_letter> == "a"'

Old-Style Quantifiers

Prior to version 1.0, Fandango supported another style of quantifiers:

• The expression forall SYMBOL in EXPRESSION: CONSTRAINT is equivalent to all(CONSTRAINT for ELEM in *EXPRESSION: )

• The expression exists SYMBOL in EXPRESSION: CONSTRAINT is equivalent to any(CONSTRAINT for ELEM in *EXPRESSION: )

with SYMBOL being a symbol (in <...>, so not a Python object) which can be referred to in CONSTRAINT.

To express that at least one letter in <first_name> should be 'a', write

exists <c> in <first_name>: str(<c>) == 'a'

$ fandango fuzz -f persons.fan -n 5 -c 'exists <c> in <ascii_lowercase_letter>: str(<c>) == "a"'

Uaavaaava Iba,429988332373036
Baaa Saaaafaaa,7487260029410777

Iaa Paaaawaaaaa,046
Bbfkmpdgfqjmcclrxekwo Rbcbmacqakisgccfoktue,22357121341599457061
Baaaaaaafaamacaaaakaa Rbcbmacqakaagccfokaae,22357121341599457061

$ fandango fuzz -f persons.fan -n 5 -c 'forall <c> in <ascii_lowercase_letter>: str(<c>) == "a"'

Faa Daa,96643

Da Caaa,52637934677908472173

Aa Da,79238034467707

Vaaa Ha,43294715

Laaa Xa,13722329885

Deprecated since version 1.0: Old-style quantifiers will be deprecated in a future Fandango version. Use all() and any() instead.