Languages with homophonous IF-clauses

Question

In English, most grammars tacitly or explicitly recognise two types of if. One of these introduces subordinate interrogative clauses:

• I don't know [if I passed the exam].

The other introduces conditional protases:

• My dad will be over the moon [if I passed the exam].

Apart from the apparent difference in meaning, the clearest difference between these two occurrences of if is syntactic. The clauses introduced by so-called interrogative if appear as Complements and the clauses introduced by so-called conditional if appear Adjuncts [read 'Modifiers' or 'Adverbials'].

This homophony between the items used to mark conditional protases and interrogative clauses is not a peculiarity of English, but occurs in many languages: Tagalog, American Sign Language and Spanish, for example.

However there is, it has been argued, a third if in English. This if introduces clauses whose internal syntax makes them seem more like conditional protases and less like interrogative clauses (chiefly because such clauses allow the use of irrealis-were). These clauses, however, appear not as Adjuncts within conditional constructions but as Complements, often within extraposition constructions (bolding etc in the following added by me):

• It would be a shame [if Bob left]. (Williams 1974, p. 158)
• It would be wonderful [if unicorns existed]. (Pullum 1987, p. 260)

In the examples above we see a meaningless dummy pronoun it functioning as Subject. The if-clauses concerned appear as Complements (here, of predicate adjectives) within the VP, but are interpreted, semantically, as subjects. As described by Pullum (1987), on their most likely readings, the examples above mean something like For Bob to leave would be a shame and For unicorns to exist would be wonderful.

Some other examples:

• Can you imagine [if people really believed that]? (Rocchi 2011, p. 1)
• I'd prefer (it) [if you came on Thursday].

The question

1. Are there other languages where clauses which seem to have the same form as conditional protases occur in other environments, for example as the complements of verbs, adjectives or prepositions?

2. If so, are any of those languages ones where conditional protases may be introduced by the same items as interrogative clauses?

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^References:

^{Pullum, Geoffrey K. 1987. Implications of English extraposed irrealis clauses. In: Ann Miller and Joyce Powers (eds.), ESCOL ’87: Proceedings of the Fourth Eastern Conference on Linguistics, October 2-4, 1987, 260–70. Columbus, Ohio: The Ohio State University.}

^{Rocchi, Manuela. 2010. A third If. University of Edinburgh MSc dissertation.}

^{Williams, Edwin. 1974. Rule ordering in syntax. Unpublished Doctoral dissertation, MIT.}