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57 lines
2.3 KiB
Plaintext
57 lines
2.3 KiB
Plaintext
# OBITools expression language
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Several OBITools (*e.g.* obigrep, obiannotate) allow the user to specify some simple expressions to compute values or define predicates. This expressions are parsed and evaluated using the [gval](https://pkg.go.dev/github.com/PaesslerAG/gval "Gval (Go eVALuate) for evaluating arbitrary expressions Go-like expressions.") go package, which allows for evaluating go-Like expression.
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## Variables usable in the expression
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- `sequence` is the sequence object on which the expression is evaluated.
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- `annotations`is a map object containing every annotations associated to the currently processed sequence.
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## Function defined in the language
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### Instrospection functions {.unnumbered}
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- `len(x)`is a generic function allowing to retreive the size of a object. It returns
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the length of a sequences, the number of element in a map like `annotations`, the number
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of elements in an array. The reurned value is an `int`.
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### Cast functions {.unnumbered}
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- `int(x)` converts if possible the `x` value to an integer value. The function
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returns an `int`.
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- `numeric(x)` converts if possible the `x` value to a float value. The function
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returns a `float`.
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- `bool(x)` converts if possible the `x` value to a boolean value. The function
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returns a `bool`.
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### String related functions {.unnumbered}
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- `printf(format,...)` allows to combine several values to build a string. `format` follows the
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classical C `printf` syntax. The function returns a `string`.
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- `subspc(x)` substitutes every space in the `x` string by the underscore (`_`) character. The function
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returns a `string`.
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## Accessing to the sequence annotations
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The `annotations` variable is a map object containing all the annotations associated to the currently processed sequence. Index of the map are the attribute names. It exists to possibillities to retreive
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an annotation. It is possible to use the classical `[]` indexing operator, putting the attribute name
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quoted by double quotes between them.
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```go
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annotations["direction"]
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```
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The above code retreives the `direction` annotation. A second notation using the dot (`.`) is often
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more convenient.
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```go
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annotations.direction
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```
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Special attributes of the sequence are accessible only by dedicated methods of the `sequence` object.
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- The sequence identifier : `Id()`
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- THe sequence definition : `Definition()`
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