Generic MathLang

Generic MathLang is meant to be an intermediate step between the Rule datatype and MathLang. See also the high-level discussion of 'Generic MathLang' vs 'MathLang' in the discussion of the Explainable codebase.

Things that get more structured from Rule. A lot of things in Rule are just free text inside a MTExpr, but it gets parsed in Generic MathLang.

Arithmetic expressions

In Rule, a single cell may contain arbitrary expressions. Compare lines 1 and 2:

SUM,foo,bar,,,,,,, (1)
,,,,,,,,,
foo + bar,,,,,,,,, (2)

Version (1) is parsed as an arithmetic expression in Rule, but version (2) is just free text. Generic MathLang parses everything it can, even inside the cells.

Records

Text like foo's,bar's,baz gets parsed into records: foo.bar.baz.

Functions

Rule may define functions as follows (see example spreadsheet for larger context):

GIVEN x   IS A Number
        y   IS A Number
DECIDE x discounted by  y IS x * (1 - y)

And we can apply the function (simplified the arguments):

DECIDE Answer IS firstArg discounted by   secondArg

When parsed into rules, we don't have much structure:

HC { hHead = RPConstraint
            [ MTT "x", MTT "discounted by", MTT "y" ] RPis
            [ MTT "x * (1 - y)" ]
   , hBody = Nothing}

HC { hHead = RPConstraint
            [ MTT "Answer" ] RPis
            [ MTT "firstArg"
            , MTT "discounted by"
            , MTT "secondArg" ]
   , hBody = Nothing}

The definition becomes as follows:

( "discounted by",
        (
            [ MkVar "x", MkVar "y" ], MkExp
            { exp = ENumOp
                { numOp = OpMul, nopLeft = MkExp
                    { exp = EVar
                        { var = MkVar "x" }, md = [{- omitted some metadata: line number, type etc. -}]
                    }, nopRight = MkExp
                    { exp = ENumOp
                        { numOp = OpMinus, nopLeft = MkExp
                            { exp = ELit
                                { lit = EInteger 1 }, md = [{- omitted some metadata -}]
                            }, nopRight = MkExp
                            { exp = EVar
                                { var = MkVar "y" }, md = [{- omitted some metadata -}]
                            }
                        }, md = [{- omitted some metadata -}]
                    }
                }, md = [{- omitted some metadata -}]
            }
        )
    )

And the application as follows:

EVarSet
    { vsetVar = MkExp
        { exp = EVar { var = MkVar "Answer" }, md = [] }, arg = MkExp
        { exp = EApp
            { func = MkExp
                { exp = EApp
                    { func = MkExp
                        { exp = EVar
                            { var = MkVar "discounted by" }, md = [{- omitted some metadata -}]
                        }, appArg = MkExp
                        { exp = EVar
                            { var = MkVar "Step 3" }, md = [{- omitted some metadata -}]
                    }, md = []
                }, appArg = MkExp
                { exp = ERec
                    { fieldName = MkExp
                        { exp = EVar
                            { var = MkVar "risk cap" }, md = [{- omitted some metadata -}]
                        }, recName = MkExp
                        { exp = EVar
                            { var = MkVar "accident" }, md = [{- omitted some metadata -}]
                        }
                    }, md = []
                }
            }, md = []
        }
    }

Types