Pattern Matching

The match strategy (?) Compares the term under consideration to a pattern. If the pattern contains variables, these variables are bound to the actual values in the term.

Special matching operators exist: # and @. They are explained in their own paragraph.

For example, ?FunDef(Id(fn),fb)

• succeeds when applied to FunDef(Id("decode"),Return(Int(0))), fn will have the value "decode", and fb will have the value Return(Int(0))

• fails when applied to e.g. term VarDef(Id("i"),TypeDecl(Int))

Matching on lists:

explained using some examples:

0: ?[x | xs] applied to [] will fail
1: ?[x | xs] applied to [1] will yield x = 1, xs = []
2: ?[x | xs] applied to [1,2] will yield x = 1, xs = [2]
3: ?[x | xs] applied to [1,2,3,4] will yield x = 1, xs = [2,3,4]

4: ?[x , xs] applied to [] will fail
5: ?[x , xs] applied to [1] will fail 
6: ?[x , xs] applied to [1,2] will yield x = 1, xs = 2
7: ?[x , xs] applied to [1,2,3,4] will fail

?[] will only succeed on an empty list []

See also

• TermProject
• Contextual pattern matching^?
• Term deconstruction^?
• Variable Scope^?