ALGOL 60 is a block-structured programming language specified through a formal report, with nested declarations, procedures, typed variables and structured statements for numerical algorithms. An identifier's meaning depends on its enclosing blocks, making lexical scope explicit. The revised report also uses a precise grammar to distinguish syntactic structure from the typography of a particular printed program.[ref]
Revised Report on the Algorithmic Language ALGOL 60 edited by Peter Naur. blocks, declarations and procedure statements
Its parameter mechanisms include call-by-value and call-by-name. The latter behaves through systematic replacement, with renaming to avoid accidental identifier capture, rather than simply copying one already evaluated value. A procedure that refers to a name parameter more than once can therefore evaluate its actual expression more than once. This matters when the expression depends on changing variables or has effects; the two calling conventions are not interchangeable.
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