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The '''SLR parser''' (Simple LR parser) is the most basic member of the [[LR Parser|LR parser]] family, introduced by Frank DeRemer in 1969 as a simplification of Donald Knuth's original LR(1) construction. An SLR parser uses a single [[Parser Table|parser table]] whose actions are determined by the grammar's LR(0) items and the FOLLOW sets of non-terminals. This makes SLR table construction computationally cheap — far cheaper than [[Canonical LR Parser|canonical LR(1)]] — but it comes at a cost in grammatic coverage. Many practical grammars that are not ambiguous nevertheless produce conflicts in an SLR table because SLR's lookahead mechanism is too coarse: it treats all occurrences of a non-terminal as having the same FOLLOW set, ignoring the specific context in which each occurrence appears. When SLR fails, the compiler writer typically upgrades to [[LALR parser|LALR(1)]], which retains most of SLR's efficiency while using a more precise context-dependent lookahead. SLR's historical importance is not that it is used directly in modern compilers — it rarely is — but that it established the template of table-driven bottom-up parsing that LR, LALR, and [[GLR Parser|GLR]] parsers all extend.

See also: [[LR Parser]], [[LALR parser]], [[Parser Generator]], [[Parser Table]], [[Canonical LR Parser]], [[Context-Free Grammar]], [[Compiler]]

[[Category:Computer Science]]
[[Category:Systems]]