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In Haskell, indentation can be used in several syntactic constructs, including do, let, case, class, and instance. The use of indentation to indicate program structure originates in Peter J. Landin 's ISWIM language, where it was called the off-side rule .
If the second sub-expression can be a further simple conditional expression, we can give more alternatives to try before the last fall-through: (x>0) -> 1/x; (x<0) -> -1/x; 0 In 1966 ISWIM had a form of conditional expression without an obligatory fall-through case, thus separating guard from the concept of choosing either-or.
1 2 3 Case-expressions in Haskell and match-expressions in F# and Haskell allow both switch-case and pattern matching usage. ^ In a Ruby case construct, regular expression matching is among the conditional flow-control alternatives available.
Haskell features lazy evaluation, lambda expressions, pattern matching, list comprehension, type classes and type polymorphism. It is a purely functional programming language, which means that functions generally have no side effects .
case expression is when value_list 1 => statements ... _ => expression» Haskell if condition then expression else expression or when condition (do instructions) or
Tagged unions are most important in functional programming languages such as ML and Haskell, where they are called datatypes (see algebraic data type) and the compiler can verify that all cases of a tagged union are always handled, avoiding many types of errors.
a list is a matched pair of parentheses, with zero or more expressions inside it. Here the decimal digits, upper- and lower-case characters, and parentheses are terminal symbols. The following are examples of well-formed token sequences in this grammar: '12345', '()', '(A B C232 (1))'
The Glasgow Haskell Compiler (GHC) is a native or machine code compiler for the functional programming language Haskell. [5] It provides a cross-platform software environment for writing and testing Haskell code and supports many extensions, libraries, and optimisations that streamline the process of generating and executing code.