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| -rw-r--r-- | doc/tut1.txt | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/doc/tut1.txt b/doc/tut1.txt index 1fa495054..500480cf0 100644 --- a/doc/tut1.txt +++ b/doc/tut1.txt @@ -757,16 +757,25 @@ However, this cannot be done for mutually recursive procedures: # forward declaration: proc even(n: int): bool - proc odd(n: int): bool = +proc even(n: int): bool + +proc odd(n: int): bool = + assert(n >= 0) # makes sure we don't run into negative recursion + if n == 0: false + else: n == 1 or even(n-1) - proc even(n: int): bool = +proc even(n: int): bool = + assert(n >= 0) # makes sure we don't run into negative recursion + if n == 1: false + else: n == 0 or odd(n-1) Here ``odd`` depends on ``even`` and vice versa. Thus ``even`` needs to be introduced to the compiler before it is completely defined. The syntax for such a forward declaration is simple: just omit the ``=`` and the -procedure's body. +procedure's body. The ``assert`` just adds border conditions, and will be +covered later in `Modules`_ section. Later versions of the language will weaken the requirements for forward declarations. |