OCaml is a variant of ML and is similar to Standard ML.
OCaml and SML
Here’s a comparison of some aspects of the OCaml and SML languages.
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Standard ML has a formal Definition, while OCaml is specified by its lone implementation and informal documentation.
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Standard ML has a number of compilers, while OCaml has only one.
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OCaml has built-in support for object-oriented programming, while Standard ML does not (however, see ObjectOrientedProgramming).
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Andreas Rossberg has a side-by-side comparison of the syntax of SML and OCaml.
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Adam Chlipala has a point-by-point comparison of OCaml and SML.
OCaml and MLton
Here’s a comparison of some aspects of OCaml and MLton.
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Performance
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Both OCaml and MLton have excellent performance.
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MLton performs extensive WholeProgramOptimization, which can provide substantial improvements in large, modular programs.
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MLton uses native types, like 32-bit integers, without any penalty due to tagging or boxing. OCaml uses 31-bit integers with a penalty due to tagging, and 32-bit integers with a penalty due to boxing.
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MLton uses native types, like 64-bit floats, without any penalty due to boxing. OCaml, in some situations, boxes 64-bit floats.
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MLton represents arrays of all types unboxed. In OCaml, only arrays of 64-bit floats are unboxed, and then only when it is syntactically apparent.
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MLton represents records compactly by reordering and packing the fields.
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In MLton, polymorphic and monomorphic code have the same performance. In OCaml, polymorphism can introduce a performance penalty.
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In MLton, module boundaries have no impact on performance. In OCaml, moving code between modules can cause a performance penalty.
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MLton’s ForeignFunctionInterface is simpler than OCaml’s.
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Tools
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OCaml has a debugger, while MLton does not.
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OCaml supports separate compilation, while MLton does not.
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OCaml compiles faster than MLton.
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MLton supports profiling of both time and allocation.
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Libraries
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OCaml has more available libraries.
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Community
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OCaml has a larger community than MLton.
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MLton has a very responsive developer list.
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